Cleaning Slate – Expert Advice on Cleaning Slate and Slate Floors – Part 1
By Ian Taylor on Mar 1, 2008 in Cleaning, Problem Solving, Slate, Stain Removal
Cleaning slate isn’t too difficult. It’s vital, however,to know what kind of dirt or contaminant you are trying to remove before you can make a decision as to which cleaning product is best suitable.
Slate comes in many different colours and finishes. Some of these are smooth whereas others have a textured surface. Undoubtedly, slate is a very popular material for flooring right now.
Slate generally has good resistance to mild acids so this gives you a much wider choice of cleaning materials than you would have with more acid-sensitive stones like limestone or marble.
So, how do we go about cleaning our slate floor?
First, you need to check whether the contaminant is mineral based? e.g. grout staining, cement, rust or general dirt. If it is, you would be advised to use a mild acid cleaner such as Phosphoric Acid Cleaner.
In most other situations where you have, for example, general dirt and grime, wax, oil or a general build up of old polishes etc. I would recommend using a strong alkaline cleaner for periodic intensive cleaning. For everyday cleaning I’d recommend using a mild, neutral cleaner.
Here’s an Expert’s 6 – Step Guide to Cleaning Slate:
1. Ensure your slate is protected with a high quality sealer such as Sealer’s Choice 15 Gold. This product will give you a natural look with a matt finish and below surface stain protection. Alternatively you can use something like Seal & Finish Low Sheen for a pleasant low sheen gloss which really helps any ongoing cleaning.
2. You must eliminate all grit – this is the major cause of all wear to slate floors. Ideally, place a dust mat both inside and outside the room which will help remove grit from shoes and prevent it from spreading to the slate floor.
3. Sweep and vacuum the slate floor regularly. This will also help remove grit from the surface of the floor.
4. Mop up and soak up isolated spillages as they happen. You shouldn’t leave strong contaminants such as coffee or wine to dwell on a slate floor.
5. Wash the slate regularly intervals using a mild, neutral cleaner. This will clean the slate but it won’t damage the stone, grout or the sealer used.
6. Less frequently, carry out a deep clean. For this, I’d we recommend using a high alkaline content cleaner. More in Part 2.
Glyn | Aug 21, 2009 | Reply
I have a grey / white stains appearing on a number of my slate floor tiles (textured grey/blue/black mix). Some were appearing before I stripped it & more have appeared afterwards. Mainly around the edges but also some in the middle of tiles. I have recently stripped it with Plasplugs tile polish remover(which I had used succesfully before) & then impregnated & sealed with HG products – again used before. Any ideas on what I need to do to remove the stains? I have a patch of the floor that I have not impregnated & sealed which also shows this marking.
Your help would be appreciated as I love my floor but am concerned I have done something bad to it!!!!
gwyneth | Mar 11, 2010 | Reply
I have slate hearth that came off a snooker table it has brown streaks that wont come off could it be rust and how can i remove them
Ian Taylor | Mar 11, 2010 | Reply
Hi Gwyneth,
It is hard to advise without seeing the slate. Some slates do have other minerals in them, including sources of iron, so it is not impossible for slate to have rusty veins within it. If this is the case it may be impossible to remove as it is part of the stone. However, if it is a rusty deposit (perhaps the slate was stored somewhere for a while and something metal was lying against it for example) then it should be removable.
Acidic cleaners are frequently used to remove rust, you could try Extreme by Aqua Mix – just pre-wet the stone, pour some neat Extreme onto the stain, leave it to dwell for a minute and scrub. Remove and rinse. – Do you have any pictures you could send me? – Might give me a better idea of the problem.
Ian
Ross | Sep 8, 2010 | Reply
I have some slate tiles installed on the walls of my shower enclosure but one of the tiles is rusting and I have noticed rust streaks / stains running down the wall and slight staining on the floor of the shower tray as a result. Any ideas how I can prevent this and clean the stains? I sealed the tiles when they were installed a year ago with about 4 applications of sealant. Thanks. Ross.
Ian Taylor | Sep 8, 2010 | Reply
Hi Ross,
OK, first let’s get the obvious out of the way; Is the rust coming from a metal fitting of any kind, like the shower outlet or slide rail for example? – If so then you have to take that down and treat/replace that.
However, some slate can create rust all by itself; within the slate there may well be some form of iron-bearing mineral, we see this a lot in the autumn and multi-coloured slate, as well as in granites and marbles, limestones and other rocks. All that is needed is some moisture and oxygen to oxidize the iron and you make rust. So the question is, is there some moisture getting into the slate? This could be through an ineffective seal (not so likely with 4 good coats as you say, although sealers are not waterproofers, they are stain resisters). Maybe there is another reason, something leaking behind and finding its way to that part of the slate, or fine cracks in the grouting, fine gaps opening up between the grout and the edge of the slate (over time with movement, no sealer will prevent this).
So have a good look, see if you can identify the source of the moisture – anything obvious – fix that first. Also bear in mind that impregnating sealers are not coatings, they will not put a barrier between the surface of the slate and the water (they are inside the slate as a stain barrier). So any iron in the actual surface will be exposed to the shower water and the problem could be that simple.
To remove it, use a mild acidic solution, preferably one based on phosphoric acid (they use this in the motor trade to remove rust from metal) so Aqua Mix Phosphoric Acid Cleaner or Substitute or for a larger problem, Aqua Mix Extreme is excellent. If it is coming from the surface of the slate then it will re-occur – just keep cleaning it until it stops, you may consider a coating sealer to add a bit of a barrier a the surface but even this may not prevent it 100%. If the problem is from some underlying leak then you have to get that fixed and then it should not reoccur.
Hope that helps
Ian
Jean Saunders | Nov 16, 2010 | Reply
I have just had a new slate hearth for my fire place, when the builders plasterd the sides of the fire place they droped plaster on the slate and now it has left white marks how can i remove them,it looks awful. Please help
Ian Taylor | Nov 26, 2010 | Reply
Hi Jean,
As long as the slate is a good one that is not acid sensitive, I would try a mild acidic cleaner based on phosphoric acid. Us it diluted as per the instructions. Do not use anything based on hydrochloric or muriatic acid, they are to strong and have dangerous fumes.
One other thing you could try is a product called Grout Haze Clean Up by Aqua Mix, I have used this neat to remove plaster dust quite effecively.
Ian
steve | Dec 19, 2010 | Reply
I have just had a gas fire installed. Now, after the fire has been used, the slate tiles on the hearth are rusting. Any ideas how I can remove this, and how can I prevent it coming back? Many thanks.
Ian Taylor | Dec 20, 2010 | Reply
Hi Steve,
The rusting is a natural phenomena with this type of slate, there are a variety slates on the market, from many different parts of the world, they can be made up of a wide variety minerals. Sometimes there are iron bearing minerals in the stone and when these are buried deep in the rock and not exposed to the air they stay unaffected. However, as the slate is split and processed for sale, fresh faces of the stone are exposed to air and water, (water from cutting, from the installation and grouting process, and even just the ambient moisture in the air). as everyone knows, when Iron mixes with water in the presence of air, it reacts with the oxygen; oxidizes – or put another way – rusts.
As this is not a stain that has been deposited in the stone, it is not quite so easy to remove. It is part of the stone, however you may have some success with an acidic cleaner, choose one based on phosphoric acid, or if you can get hold of it, Extreme by Aqua Mix, follow the instructions on the bottle. If successful, dry the stone so it is free of moisture and then consider sealing the slate, to help manage the amount of moisture that the slate is exposed to in the future.
Amanda jane | Jan 2, 2011 | Reply
I have a limestone floor in my conservatory and before we put the floor down we washed it all with relevant cleaners you can buy then once down and grouted we covered whole floor in a selant, however I have knocked a home oil freshner over and it has put a slight yellow tinge to the floor, when it happen I soaked as much as I could with kitchen roll and then washed the floor down with plain water, however this hasn’t cleared it, everytime I mop with plain water it releases the smell of the oil again, any ideas how to rectify?
Ian Taylor | Jan 4, 2011 | Reply
Hi Amanda,
OK you are going to need a degreaser for that, hopefully your sealer has done its job and is keeping the oil at the surface. First get q good degreasing cleaner like Heavy Duty Tile & Gorout Cleaner by Aqua Mix or similar (high alkaline), mix in accordance with the on bottle instructions. Then apply to the oil and leave it to sit for about 15 minutes. Then scrub and mop up. Now rinse with cleaner water and mop up. Dry the floor and inspect, it should have remvoed much if not all of the oil. It may be wise to top up the sealer in that part once dry.
Hope that helps
Ian
Gillian Phillips | Jan 9, 2011 | Reply
Have just installed an unsealed slate floor in my bathroom but before I had chance to seal it someone has missed the pan and it now has some dark urine marks on it. I rinsed the area with warm water, to no great effect.
How can I get these out, and what sealer is best for a matte finish?
Ian Taylor | Jan 10, 2011 | Reply
HI Gillian,
I would try a high alkaline cleaner (such as Heavy Duty Tile and Grout Cleaner). Pre wet the floor, particularly the area around the stain (so as to fill up the tile with water and get underneath the stain). Then mix the cleaner as directed (I would use about 1:4 with Heavy Duty Tile & Grout Cleaner), apply the cleaner to the floor, leave it to sit their for about 15 minutes. Now scrub the area with a nylon scrubbing brush.
Pick up the dirty water with a mop or sponge, now apply clean fresh water and scrub again lightly, then pick up that water, thus rinsing the floor.
Allow it to dry thoroughly before inspecting the stain. If it has gone great, if not repeat the process and maybe add a little nanoscrub.
In terms of a mat (natural look) sealer – I would recommend Sealer’s Choice Gold – it is water based and this will work well on such a porous stone. It will not add any colour, nor any shine or finish. For a darker, enriched colour look (but still no shine) go for something like Enrich n Seal – but make sure this is the look you want (like a very wet slate, but with the surface moisture removed) as there is no going back.
Hope this helps
Ian
Julia | Jan 18, 2011 | Reply
I have a shower room with black polished slate on the walls and my cleaner has sprayed limescale remover on the walls! (arrgh!) it has left White splats where she sprayed it. Please can you advise me of how to rid of these marks?
Many thanks,
Julia
Ian Taylor | Jan 18, 2011 | Reply
Hi Julia,
The white ‘splats’ are more mineral deposits – the result of not rinsing the limescale remover (which I am going to assume was acidic). OK, as long as the limescale remove is not based on HCL (hydrochloric acid) then you could use it again. What has happened is that the acid has dissolved the limescale and then been left to dry and so the liquid has evaporated and the mineral (limescale, and/or other salt from the reaction) has been left behind.
So: pre-wet the slate, then using your limescale remover (or something like this if not) spray your cleaner onto the affected area, wait a couple of minutes, scrub with a white nylon pad or scrubbing brush. Now, your cleaner may have got this far, so here is the important bit: rinse all trace of the cleaner away with fresh water, should be easy in a shower.
Now it is a good idea to take an old towel and rub down the slate. Let it dry and see if that helps.
Ian
Emma Evans | Mar 5, 2011 | Reply
Hello,
We have just taken delivery of a polished piece of welsh slate (heather blue colour) for our hearth. It seems to have some small, whitish / very light green circular marks on it. We are not sure wether these are part of the make up of the slate or are a type of stain. Would it harm the slate to try to clean them off with anything. As we don’t know what may have caused them we are unsure what to use.
We have asked the quarry about this but they say it is natural, it just doesn’t look very natural – it looks more like something has been spilt on it.
Have you any idea what it could be or wether it is indeed part of the slate?
Many thanks,
Emma
Charlotte | Mar 8, 2011 | Reply
We have just had a slate hearth put in and before we’ve had chance to seal it I have spilt some distilled vinegar onto it. Just a small area about 4cm x 3cm. The slate returns to its dark charcoal colour when wet. I.m guessing that the surface is etched but still feels smooth. What can I do? I’ve seen some advice to use polishing powder but where do you get this from?
Ian Taylor | Mar 9, 2011 | Reply
Hi Charlotte,
If it is good quality slate, it should not have etched, but the acid in the vinegar may have taken something out I guess. I am not sure polishing powder is the best way to deal with it, that would mean re-polishing or honing the entire surface most probably and that is really a professionals job as you need the right equipment to do it and it takes practice to get good results. If it returns to the tight colour when wet then perhaps using a colour enhancing sealer (like Aqua Mix Enrich n Seal for example) – provided the stone has not been sealed as you say this could be the answer as it will have the same darkening effect as water but it will be permanent.
Hope that helps
Ian
Ian Taylor | Mar 17, 2011 | Reply
Hi Emma,
Actually, I know this slate quite well and have worked with it personally several times. The light green circular marks are, I’m afraid, very commons and 100% naturally occurring – like veins in marble – they are just a part of the stone. The slate is made up of various materials including clay and other minerals, originally laid down as a sedimentary rock, then subjected to low grade metamorphism. The light green spots are concentrations of certain minerals and you will find they go through the stone (a bit like choc-chips in cookie dough) so they are not going to be cleaned off the surface. If you were to cut away or split the surface to a depth that would remove one green spot, you will most likely uncover several more.
I can understand your disappointment, particularly if you were not made aware of this before purchase – maybe you have an argument from that perspective? As it is a singular piece for a hearth (as opposed to 100′s of m2 for a floor) it is perhaps not unreasonable to ask the quarry to take the time to ‘sort’ through pieces to find one that is more uniform in colour – that would be my opinion, but I do not know if they would do this for you.
Ian
Nina | Mar 22, 2011 | Reply
I had the chamber of my fireplace lime rendered recently, I have small deposits of the plaster on my natural slate hearth and no amount of scrubbing fetches it off, could you advise of anything that I could remove it with. Thanks
Ian Taylor | Mar 23, 2011 | Reply
Hi Nina,
I have found Grout Haze Clean Up by Aqua Mix very effective for removing plaster in the past, if you can get some it might be worth a try. Failing that I would try a more direct acid-based cleaner – something like Phosphoric Acid Cleaner/substitute again by Aqua Mix – or other equivalent – but NOT a cleaner based on hydrochloric acid (HCL) such as used in many brick cleaners – it is far too strong and the fumes can damage metal finishes.
Hope that helps
Ian
Rupert | Apr 25, 2011 | Reply
Ian
I have what I am pretty certain are textured slate tiles on my balcony floor. Between the tiles there has, over the years, built up a whitish residue from frequent rinsing with water. The balcony is pretty much protected from the elements. Living in London as I do, with its extra-hard water, I imagine this residue to be limescale – it certainly looks like it.
The surface of the tiles looks generally ok although there appears to be a slight ‘haziness’ to it and could do with some improvement.
I am writing to enquire whether you know of the best product to use to treat both issues but predominantly the residue between the tiles.
I look forward to your reply.
Many thanks.
Rupert
Ian Taylor | Apr 27, 2011 | Reply
Hi Rupert, on the face of it this sounds fairly simple and your ‘diagnosis’ sounds fair (from your information it does sound like hard water deposits building up over time, rather than efflorescence coming up from below). Provided your slate is not acid sensitive (some of the multi-coloured rusty looking ones can be a bit sensitive to acids) then a mild acid cleaner, dilute with water should do the trick in one application.
First you need to make sure you get the right acid-based cleaner – DO NOT buy a brick cleaner, or a cleaner from a builder’s merchant that is based on hydrochloric acid (HCL)- it is far too strong and the fumes alone can damage metal finishes. So for example you could buy Phosphoric Acid Cleaner (or Phosphoric Acid Substitute) from Aqua Mix (no longer being brought into the UK but http://www.allforstone.co.uk has plenty left).
Do A Test First!
Mix some of the Phos Acid Cleaner say 1:5 with water (that is 5 parts water), apply it to a small test areas on both the slate and the joint. You may see a small amount of effervescence (fizzing or bubbles being generated) this is just the acid reacting with small amounts of cement in the grout joint (it is actually etching the grout at a very low level, no real damage will result unless the grout is weak or poorly installed – but it might lighten the colour slightly- this is unavoidable).
Leave it for a couple of minutes the scrub lightly with a scrub pad, rinse with fresh water and let dry. The rinsing stage is crucial, as the mild, dilute acid will quickly dissolve the lime-scale but it will also dissolve a tiny amount of cement from the grout, in the process a by product, a salt from the reaction of the acid and the alkaline cement, will be produced. So the liquid solution will have slats and diloved lime-scale in it, if you just allow it to dry you get that residue re forming on the surface and the floor could look even more white and patchy than before – so: apply; dwell; agitate; remove; RINSE and then for good measure, dry – use an old towel or something to pick up the rinsing water. This takes both the remaining water and any traces of residual acid/limescale/salts etc.
Let it dry thoroughly; check for damage to the slate (doubtful) check to see if it has cleaned all the limescale away – for example one application may easily remove the fine haze from the slate, but it might take two applications to get it all from the joints.
You can always vary the dilution; if you found that one application cleans it up 100% really easily, then try a 1:10 mix (the less acid you use the better, and you make the product go further also). If it struggles make it a bit stringer, say 1:3. IT is better to do 2 weak applications than one really strong one.
If your test is successful, then repeat the above process on the rest of the floor.
Hope that helps
Ian
Rupert | Apr 27, 2011 | Reply
Ian
Thank you so much for your time and attention.
I shall follow your helpful instructions/advice precisely.
Regards
Rupert
Paula | May 1, 2011 | Reply
Hi Ian, We brought our house 8years ago and the fire place has a black slate surround, it is looking dull now. I am unsure how to bring it back to life. I have been cleaning it with just soapy water and drying it off.
Please could you give me advice.
Thank you
Paula :0)
Ian Taylor | May 3, 2011 | Reply
Hi Paula,
The type of black slate typically used for this is dense and can be honed to quite a smooth finish, not a high shine, but what we call a fine hone: flat, smooth and with a satin sheen rather than a gloss. on a floor this can of course wear and dull down through mechanical means, however on a hearth, and certainly a vertical surround, it is not subjected to this kind of wear (unless you are particularly vigorous in your cleaning) -so the dullness is more likely to be a build up of ‘something’ on the surface. This can often be residues from cleaners.
The first thing Would try is a high alkaline cleaner (like Heavy Duty Tile and Grout Cleaner) maybe with a bit of a cream abrasive like nanoscrub added. Apply it dilute as per instructions, keep applying it with a sponge for 5 minutes or more (to keep the vertical surface wet) then use a white nylon polishing/scrubbing pad and lightly scrub the area. Rinse it down with clean water and rub dry with a clean towel.
Try this first as it may remove a semi invisible ‘scum’ that could have built up over the years. If this does not restore the stone, then come back to me.
Hope that helps
Ian
Rob | May 12, 2011 | Reply
Hello Ian
I’ve read through all your great advice on this page but still have a question I hope you help with?
I tiled the inside of the shower enclosure using random (Indian I believe) slate or different colours textures and density it seems. I was very meticulous with the tiling, and machine cut each tile, set them in a deep bed of cement (they are random thickness and riven) and achieved and excellent 3mm grout line throughout. I actually masked lines of tiles when grouting to avoid mess. Finally I sealed the tiles with 3 coats of Fila slate impregnator upon completion.
One thing I neglected to consider is that I live in a hard water area of the UK (South Coast – so water is filtered up through chalk boreholes).
After a couple of years the shower is not looking as hot as it did, and the main problem appears to be limescale clinging to the rough surfaces of the tiles. This gives the appearance of a dry salty coating when dry, but disappears once the tiles become wet.
I would like to remove this film, but am very wary of cleaners after making the mistake of cleaning the chrome shower control with LimeLite. I obviously didn’t do this with much care or rinse it correctly, as it left some light staing to the tiles and grout immediately below the faucet/control.
I appreciate it may be harder to advise me because of the composition of the random slates I’ve used, but if you can offer any advice it would be much appreciated.
The really affected areas are on the wall directly below the showerhead, the rest and high up aren’t so bad.
Kind Regards
Rob
Ian Taylor | May 13, 2011 | Reply
Hi Rob,
I just tried to find out what the chemical composition of Limelite is – and there is no SDS on their web site. It does state not to use the product on marble or limestone – so, given that and that it is designed to remove limescale, we can safely assume it is an acid-based cleaner of some kind. My question though is what acid? If it damaged your chrome, then it is strong, and quite possibly something like HCL (hydrochloric).
HCL can cause all kinds of damage, in fact the fumes from such a product alone can dull metals. But since we do not know what they use in that product, we should not speculate.
What I can say is that a cleaner based on a weaker acid such as phosphoric will usually present no such problems. Products like Aqua Mix Phosphoric Acid Cleaner (there are a lot of similar products out there) contain about 22% phos acid, and they are normally diluted further for use. Such products are usually perfectly safe.
In your case, you may well have to resort to such a product as a build up of calcium film (for that is what the limescale is) will really only be broken down chemically by an acidic cleaner. You could try an off the shelf cleaner based on lemon juice but that is citric acid and believe it or not that can be quite potent.
you could try a mild abrasive, like nanoscrub – this is completely non destructive and works purely through mild abrasion however my guess is that after 12 months of build up, you will probably need an acid clean first, thereafter, a product like nanoscrub will be ideal for say monthly maintenance, helping to prevent future build ups.
So, test a safe, phosphoric acid cleaner in a small area, read the on bottle instructions and try a very dilute solution first. my procedure for this would be:
1. dilute the phos acid cleaner say 1:5 with clean water
2. pre-wet the slate
3. apply the dilute solution to the slate with a sponge, brush or even a small spray bottle, leave it for a few minutes – 5 should be plenty. Keep it wet in that time, with more solution if needed (esp if on a wall)
4. now using a soft scrub pad or brush, lightly scrub the area
5. rinse with clean water
6. dry with a towel
when thoroughly dry inspect the area, if no or little improvement make a stronger solution of the PAC, say 1:3 or 1:2 (you can use it neat but there is no need to use more than you need to get the job done).
Only word of caution is that the acid may affect both your slate and the grout, to a minor degree: The cleaner works by reacting the acid with the very alkaline calcium, but it will also react with the calcium in the cement of the grout, however it is only going to be very weak and the acid is very quickly exhausted or ‘spent’ (one of the reasons why there is little point waiting more than 5 minutes for it to work). In reality this means it will do little more than chemically scrape the surface of the grout (cleaning it up too – it is a bit like using T-cut on a car’s paintwork), also, before it can react with any cement, it will have to get through the calcium deposits that are no doubt on the surface of the grout also. So the worst you should expect is a slightly brighter, cleaner grout joint.
Also, if the slate is a multi-coloured Indian type, and some of those colours are rusty brown, then they may be affected slightly too. They are rusty brown for a reason – it is actually rust – well kind of anyway, there are all kinds of minerals present in the clay/shale that the slate used to be, including iron. Having been split into the ‘slates’ and exposed to the to the atmosphere (oxygen and moisture) the little bits of iron oxidize and create the rust. Well, phosphoric acid loves rust and will react with/dissolve that too.
Again, the effect will be minimal, the acid will quickly ‘tire’ and there will be more ‘rust’ than it can remove but it may lighten it a touch.
Finally, make sure to keep the acid cleaner away from any other acid sensitive surface – you won’t have any problems with fumes and it is nowhere nears as dangerous as an HCL based product, but anything that is sensitive to acids will react – so keep away from polished marble for example. Chrome and other metals should be OK – but always best to be cautious – hope this helps
Ian
Paula | May 21, 2011 | Reply
Hi Ian
Great website by the way. I have a black slate fireplace at home and we accidently spilled a glass of champagne in it a few weeks ago.
It wasn’t cleaned up immediately and now leaves a white stain (I am guessing the acid from the wine has caused this)
Could you give me any advice on what products are available on the market which may attempt to remove this.
Thanks in advance for your help.
P
Ian Taylor | Jun 1, 2011 | Reply
Hi Paula,
Sorry about the delay in responding – I am getting so many comments now it is becoming a full time job answering them. I am not sure the problem here is acid as many black slates are pretty insensitive to acids.
If it is as a result of the acidic champagne, then it is not so much a stain, but an etch. An etch simply means that some of the stone (or the finer particles from the surface) have been affected, or to put it bluntly, dissolved, by the acid. It is a kind of chemical burning an unlike a stain which is a deposit of something left behind ON the stone, an etch is parts of the stone having been physically removed or at least altered – so there is nothing t ‘get off’.
If, it is an etch (typically it will look dull, feel less smooth to the touch and will be greyed-out in terms of colour, all compared to the rest of the stone) then the only real way to fix it, properly that is, is to refinish the surface. This means mechanical griding/honing/polishing with abrasives, most likely diamonds pads. This is usually done by professionals mainly due to the cost of buying the diamond tools required. IF the hearth is movable, you may be able to take it to a stone company (such as a granite worktop fabricator, or a gravestone/monumental mason’s establishment as they could bench finish the slate again for you) otherwise you may need a stone restoration professional to come to you in order to do it on site.
One ‘cheat’ ( and I say that with tongue in cheek) that can sometimes help is to colour the etch with a good colour enhancing sealer – this can be effective if the slate is sealed with the same sealer in the first place, or it is as yet unsealed and you treat the whole thing. I describe it (perhaps unkindly) as a cheat simply because it masks the problem, rather than fixes it – but it is a perfectly valid solution – it is also easy to do and you could do it yourself. You would first need to clean the slate and let it dry thoroughly.
If, on the other hand it is not an etch, but simply dried residue from the champagne that has got into the slate’s micro-texture – then try cleaning with a mixture of a high alkaline cleaner and a cream abrasive such as nanoscrub- I should have put this sentence first in hindsight!
Hope this helps, please come back to me if you need further assistance.
Ian
Ian Cannon | Jun 18, 2011 | Reply
At present I am having a slate floor in the front porch of my home.It is semi open to the eklements. It is approx 8ft X 3ft. It has been laid and there are iron rust deposits quite visible on two of the slates. The builder says that they can be cleaned. As this is rust::
Can it be cleaned
Will it rust further and show more.
Should I insist that he remove them and replace.
Chris | Jun 20, 2011 | Reply
Hi Ian
Very pleased I found this site – I’ve been searching the Internet for an hour!. Hope you may be able to offer some advice to a novice – we have purchased a house with slate flooring in the kitchen and the grout definitely needs cleaning. I purchased some HG grout cleaner that contains NTA (nitrilotriacetic acid) – will this damage the slate? I see you recommend phosphoric and staying away from HCL, but any thoughts on NTA?
I also have some Plasplugs tile sealer – would this help, and should I use this before or after the grout cleaner?
Thanks in advance,
Chris
Ian Taylor | Jun 21, 2011 | Reply
Hi Ian,
Some slate can contain iron bearing minerals as a naturally occurring component in their matrix. When the slate is split (to make the tiles) and thus a fresh face is exposed to the elements and cleaning water etc, the iron can oxidise – and so form rust. If this is the case then yes it can be cleaned to some extent, usually with the help of a MILD phosphoric acid based cleaner. But it may only remove the surface oxidisation, and not the rust from within the surface, or the source of the iron, so it will oxidise again. This is natural and on large areas it would be impractical to remove every affected stone, but if it is just two tiles in a small porch, I personally do not think it unreasonable to have them swapped out (the replacements could be the same though, of course).
If it is a rust deposit that has come from outside of the slate (something rusty left on it, or rusty straps on the crate in which the slate arrived into the UK for example) then you may well be able to clean it off and not have it re occur.
Hope this helps
Ian
Ian Taylor | Jun 21, 2011 | Reply
Hi Chris,
From what I can tell (and I am no chemist) that is used as a chelating agent – like a water softener – so not an aggressive acid – it is probably in there to help ‘grab hold’ of calcium and some other mineral deposits – I would love a chemist to come on and give us a better explanation
In any case I think it is perfectly safe to use, but I think for general deep cleaning of existing grout, a high alkaline degreaser would be more efficient.
Regarding the sealer, you don’t say which one it is, I think they have a coating sealer – leaves a satin-type finish, or an impregnator – soaks in and gives below the surface protection, but no actual surface protection and no sheen. So a lot depends on how you want it to look. Also, I understand that that company is no longer in existence, so you might want to test the product on some spare slate, as you cannot be sure how old it is, and if you run out, you may not be able to get any more. Their business was taken over by another company and sold through a very big ‘shed’ but I do not know for certain if the formulations are the same.
Hope this helps
Ian
Abdul kadir | Jun 23, 2011 | Reply
Hi Sir
I my self Abdul
Kadir working in KSA in KING Abdula university Of science & Technoligy with Saudi Oger LTD company as a Group leader In Housekeeping Department
There in the university they had use an egyption stone on flore & it it is very difficult to remove the stain when the stone absorve the stain
Sir please give some advice for removing the stain
Thanks & best regard
Rob | Jun 23, 2011 | Reply
Hello again Ian
Just to follow up on the kind advice you gave me with regard to removing limescale from the slate tiles in my shower enclosure, I’d just like to say that it was a complete success.
I kept it as simple as possible using your advice as a guide, so…
1. Strip off, have a shower to get the tiles good and wet.
2. To a wet soft’ish nylon scoring pad I applied a small amount of Limelite and gently scrubbed the tiles in vertical and horizontal movements.
3. Leave for about three minutes
4. Shower again, rinsing all the walls off.
5. When dried the tiles were almost scale free, although the grouting has suffered slightly and turned white’ish in places.
Many many thanks for your advice
Rob
Lynette Zito | Jun 24, 2011 | Reply
Hello Ian
I have woodburning heater with a slate hearth. My sister, a zealous cleaner, was attempting to clean the glass door on the heater and split methalyted spirits on the slate. I now have a whitish splash mark on the slate at the front of the hearth. Would really appreciate your advice.
Thanks
Lynette
Ian Taylor | Jun 24, 2011 | Reply
Hi Abdul,
The Egyptian Limestone is very nice, but as you say it is also very absorbent, especially if it is not sealed. But, even if it is sealed with an impregnating sealer it is so porous that you can still get surface staining.
You do not say what the stains are (coffee, food, general dirt etc), but the first thing I would try is a high alkaline deep cleaner, allow it to dwell on the surface for a while, then scrub lightly with a white hand pad, or a white pad on a rotary machine. Use a Wet Vac to pick up the water, then rinse with fresh clean water, then dry the floor with towels.
I would also try adding some cream abrasive (check it is designed not to scratch the limestone).
For isolated spot stains, try using a poultice ( you can buy poultice powders to mix with water of alkaline cleaners, or ready made poultice pastes) Apply the poultice to the stain, cover with plastic and leave for 24 to 48 hours, remove and rinse.
Hope this helps
Ian
Ian Taylor | Jun 24, 2011 | Reply
Excellent!- thanks for letting us know
Ian
Ian Taylor | Jun 24, 2011 | Reply
Hi Lynnette,
Interesting one this. Usually a solvent like Meths would not leave a white mark on the slate, (often Meths is coloured violet and so the pigment/dye and even the oiliness of the meths itself can make its presence felt in light coloured materials).
So, a couple of things come to mind: 1, if the slate was what I would call a low grade slate (nothing wrong with that), by which I mean a relatively young (geologically speaking) stone, they are sometimes not as dense, more colourful, more porous than older slates (like Welsh slate, or the green Vermont Slate for example) then I have seen some, where the minerals that make up the colours in the stone are not shall we say, ‘fixed’ in other words they can be washed out (we see this when using acidic cleaners on rusty coloured slate, the acid removes some of the iron and thus reduces the colour intensity). I have not seen a solvent do this but I would guess it is at least conceivable that some mobile pigment could have been removed. If this is the case, and I have to say I am very doubtful, then there may not be a whole lot you can do about it, unless you can get an enhancing sealer into the stone. This may not be possible if the slate has already been sealed. I guess the worst case scenario would be getting the slate re-surfaced by a pro.
2, I am not sure if your hearth has been sealed, either by yourself or the supplier, if it has then a much more plausible explanation could be that the meths has simply stripped, or partially stripped some of the sealer. Often coating sealers will take several attempts to break them down using solvent based strippers, the first attempt simply removes the top layer, leaving them damaged, and often, turn a kind of ‘dried on milk’ colour. If you think this could be the case, try dabbing a bit more solvent (preferably a stripper designed for removing sealants from stone). See if you remove the white stains. If so you may find you have to do the whole hearth, then reseal.
One more thought just occurred to me, what was your sister cleaning? If she was cleaning something above then the meths would be presumably, breaking down some contaminant on some higher surface, so what actually dropped down onto the heart was meths, along with whatever was now dissolved in the meths – a soluble contaminant. The meths then evaporated leaving behind whatever it was carrying. Again, dab a bit more meths on a cloth (or better still a stone stripper) and rub the white patch – you are not going to make the situation worse, as if it does not work, then it is possibly one of the above scenario’s anyway.
Hope this helps
Ian.
Suzanne Elliott | Jul 24, 2011 | Reply
Hi Ian,
I have a slate floor in my bathroom that has been sealed. I have just spilt a bottle of nail varnish remover on it and it has now come up as a massive White stain. I wiped it up straight away but the White will not go away. I’ve tried using tile stripper to remove it but when dry, the stain comes bk. I am gutted. What can I do?
Ian Taylor | Jul 25, 2011 | Reply
Hi Suzanne,
My quick appraisal of this is that the acetone in the nail varnish remover, has partially stripped the sealer ( I am assuming it is a coating sealer). We often see this on thick coatings, a stripper (usually a solvent, and Acetone makes a good stripper) can sometimes need two or three applications to completely remove a sealer. The first application kills the shine and effectively damages the coating, by taking a thin layer of it away – in doing so it makes the rest opaque/white etc (it is a bit like when you peel old tape of a surface and instead of coming away cleanly, it delaminates and leaves part of itself on the surface)
So, repeating the process shoold remove the rest of the sealer – just as a test, try some more nail varnish remover on the white marks, leave for a few seconds then rub with a cloth/scrub pad. If it works, or appears to reduce the mark then you are on the roght track. It may be that the stripper you tried is not as strong as the acetone or you may have not left it on for long enough – persevere with several applications. I would suggest doing this up to the edges of the tiles affected. When removed, rinse with water and allow to dry completely. They re-seal.
The point is I do nothink yo have damage the slate in any way, you have damaged the sealer alone, in my opinion.
Hope this helps
Ian
Kevin | Aug 13, 2011 | Reply
Ian,
I recently black slate floors installed in my bathroom. Marble was aslo being laid in the bathroom at the time around the shower and tub. When I was first able to see the floors there were blue spots that looked like stains – the spots/stain were in an oval shape and not the pattern of the stone. The builder told me the spots were in the stone, however when I selected and ordered the stone from the stone company we were shown 4 slate tiles and told the color variation would only be between the 4 tiles. None of the variations included any blue spots. Were the spots part of the original stone? Can the spots be removed?
Ian Taylor | Aug 16, 2011 | Reply
Hi Kevin,
From your description (and I do not know if you are UK based or not, nor do you tell me which slate you have) I would say it is actually quite likely that this is in the stone. For example, with Welsh slate (renowned as among the best slate in the world) these blue/green oval markings are quite commonplace and are a naturally occuring due to minerals in the stone.
If you have these, and I suspect that you have, then no, there is no way of removing or masking them, you will find that if you were to cut through through the sotne, the marks would extend all the way through the stone. They are perfectly natural and not technically ‘faults’.
On the issue of what you ‘thought’ you were getting, I can sympathise, maybe you have a case that if these blos are naturally occuring, the vendor should perhaps have shown you a more rerpresentitive sample in my opinion – but that is one for legal advice
hope this helps
Ian
Graham | Aug 26, 2011 | Reply
Dear Ian, We have just laid a blue/black slate patio (chinese/Indian slate bought from Ruscrete). Unfortunately, we had to lay the slate before the external patio walls could be rendered. We’ve just experienced a lot of wet weather and although plastic sheeting was laid down to protect the slate, the sand/cement mixture has washed over the slate and appears to have stained it white. Its a riven slate. I should also state that the slate has not been treated with any coatings etc. Any advice much appreciated. Best wishes. Graham
Ian Taylor | Aug 30, 2011 | Reply
Hi Graham,
There is probably, really only one way to solve this and that is an acid clean, Suggest you use a proprietary (mild) acid based cleaner, one based on a safe acid like Phosphoric or or one of it’s alternatives. Unless the render splashes are really thick, avoid using a brick cleaning acid based on HCL if you can. If you have to use one, take care and keep it away from anything metal like furniture and frames etc.
Generally the milder and weaker [the acid cleaner] the better [for the floor and grout joints] – even if it takes more cleans/ several attempts. Some indian type slates are multicoloured due to exposed (and therefore oxidized) minerals like iron (hence the rusty colour). Giving them a good scrub with even a mild phos acid cleaner can diminish some of the colour (because it cleans rust away as well as cement) but in time as the slate is left to oxidize, some of this will come back.
Given the slate is not sealed , it will be very porous so pre-wet the floor – a lot, (this is important) before putting the cleaner on otherwise it will dive into the stone and you will just waste time and product. Apply the dilute cleaner (read instructions and gove for weakest strenght first, make it stronger if needed) typically try a 5:1 mix (1 part acid cleaner to 5 parts water) and see how you get on. The more acid you use ( and you could use it neat, as most acid based cleaners like this are already only circa 25% acid the rest is water and detergents etc) the faster it may work, but the more likely it is to kill some of the colour of the slate, and have a ‘bleaching’ or whitinening effect on the grout joints.
Let the acid cleaner sit for just a few minutes then start scrubbing. For large areas out side I would recommend hiring a rotary scrubbing machine with a hard to medium brush head. Scrub, then using a hose/pressure washer and squeegee, rinse the cleaning solution away – DO NOT JUST LET IT DRY.
Then repeat if needed – you may have to do this several times – better to take small layers several times than go in too strong and dmage the slate/grout etc.
Finally rinse again with water. Some whitening of the grout may result but this will weather and dull down again quite quickly. Watch out for efflorescence – white mineral crystals forming in the joints due to all the water that you are going to need ot use. If you do get this, you can treat the floor with an efflorescence cleaner and inhibitor called Eff Ex – act as soon as you see it, otherwise you would need acid again and that could just kick off more efflorescence – it can become a viscious circle.
You can ge the products you need, including the Eff Ex at All for stone (see link ad) they may not have them all listed so give them a call.
Hope this helps
Ian
Nick | Sep 15, 2011 | Reply
Dear Ian – i have just laid some honed Brazilian slate in a shower room. I wasn’t too sure whether it needed sealing but I have done it anyway. On the first attempt I left it too long and it left a residue (i.e. you could see shoemarks). I took the sealant off with Lithofin remover and sealed again with lithofin stain-stop, this time just covering each tile and wiping off almost immediately. The effect is better but I still get faint boot sole impressions on the tiles. Can I do anything about this?
Many thanks
Nick
jo | Sep 15, 2011 | Reply
hye we have had black slate layed in kitchen they havent been treated yet we nd to get the white marks out of the slate first we have usd grout residue remover but you can stil see the white any ideas on how to get rid of the white marks?
tom mcculloch | Sep 20, 2011 | Reply
we have a one year old slate hearth which was sealed by the supplier with WD40. During the recent storms rainwater came down our chimney liner and settled on the slate hearth for a couple of days. We have been left with stains on the hearth and white marks where some of the rainwater has dropped on to the front of the hearth in our attemptg to clean. we checked with the installers who told us to wash with warm water and detergent and use a nail brush to scrub but it is making no difference,
can you help
Ian Taylor | Sep 20, 2011 | Reply
Hi Nick,
It could be that the slate is very dense, and not in need of much sealer, and so this makes getting the sealer in difficult, or at least what can happen is that the slate takes in very small amonts of sealer (all that it needs) and leaves a film on the surface. Then, you, think that yo have taken 100% of the surplus off but, more often than not there are traces left that you cannot really see. ( it takes a bit o practice and lots of changes of cloths etc to remove all the residue effectively – most people, even in the trade will always leave somnthing behind. If this is the case then the residue could be holding small particles of sweat/skin oils etc to leave the ‘footprint’
You could try using a mild detergent or even a mildly abrasive cleaner like Nanoscrub or Microscrub (contact all for stone by phone for details, see advert on the top right) .
Also, it could be that the slate surface, whilst appearing perfectly flat and smooth, is actually micro-textured – has tiny pores and surface texture that is too small to see, but big enough to grapb tiny particles and hang on to them – in this case they are not stains, but just trapped dirt and a good stiff brush (again with some Microscrub) could be the answer.
Hope this helps
Ian
Ian Taylor | Sep 20, 2011 | Reply
Hi,
I am assuming that the white marks are grout residue. If so then you may need to use the grout residue remover several times – as it will be a mild acid (and don’t be tempted to use a strong acid/brick acid or any other hydrochloric acid based cleaner). Such mild acid cleaners are designed to do the cleaning with minimal damage to the grout in the joints (which is exactly the same material as that which you are trying to break down on the slate) – so it is often necessary to repeat the clean several times, each time taking a bit more away. Also you may need to use a scrubbing brush.
Hope this helps
Ian
Ian Taylor | Sep 20, 2011 | Reply
Hi Thomas,
Well first of all WD40 is a great product – but not for sealing slate! – I can see the thinking, an oil thinned with solvents, a bit like a sealer, except the oil is designed to be a lubricant (yes also a water repellent) but it does not form a polymer film – an inner skin to keep stains out. Also, I do not imagine it lasting too long either – it will remain mobile (not ‘set’ or cured like a sealer) so it will be removed with normal cleaning over time, it will even gradually just degrade on its own – so all in all – not an effective sealer (bit of a trade ‘cheat’ in my opinion).
OK, the white marks could be due to some impurity in the water, if your chimney is limestone, for example, water could have picked up some soluble lime (and depostited it on the slate as the water evaporates) or if you live in a hard water area you could have a high calcium content (don’t think Glasgow does mind you) again you get calcium deposits left behind. Or it could be residue from detergent.
It could also be that the WD40 oil slightly darkened your slate and the sitting water has washed more out of it in those areas. Do the white areas disapear (albeit temporarily) when the slate is wet? – if so try a little acidic liquid – like a clear vinegar – just to see if there is anything mineral (the acid will disolve it), rinse and dry and look at it again. if it has lessened the problem, get a mild acid based cleaner and try that.
Conversley the white marks could be caused by acid etching – acid rain being the culprit or (and I am no chemist) I beleive it may be possible that some forms of soot, (depending on several things) can have a low ph (acidic) although often they are alkaline – so rain water picking up soot, can become acidic which could on some slates cause a slight etching. The reverse could be true also, if the water + soot resulted in an alkaine solution – that would have the effect of stripping out the WD40 – or what remained of it.
If acid etching then masking the etch marks may be an option, if all else fails, try adding a bit more WD 40 – as it was used before, it may top up the oil and make the look more uniform – not ideal, (this is where I would normally recommend an enhancing sealer but it is too risky now, the sealer mey not penetrate correctly due to he presence of the remains of the WD40) but it may mask the marks.
Hope this helps
Ian
Nick | Sep 26, 2011 | Reply
Hi Ian – many thanks for your reply…it’s very helpful. I’ll try a mild detergent and hope that works. I’ve noticed that the residue seems to be gradually improving now (after about 10 days!)…so am hoping that, with a bit of detergent, the problem might go away.
Thanks again,
Nick
Charlie | Sep 30, 2011 | Reply
Hi, in trying to be helpful my teenager washed the kitchen slate floor with a product callede Cillit Bang leaving bloches and stains all over a wide area, is there anything I can do to renew the appearance thank you
Ian Taylor | Oct 4, 2011 | Reply
Hi Charlie,
I have heard so many storeis about this product, itis not that it is a bad product, just that it contains acid and should not be used on acid sensitive surfaces (like many stone and grouts).
So, what could have happened? Well, if the slate is a coloured vairiety, with the colours coming from minerals such as iron etc, then an acid can dull and etch them, taking with it some of the colour intensit which could leave the slate looking drab. If you have white patches then there is another possibility, that there was a feint, barely noticeable grout haze or other film on the surface and the acid has etched this rather than the slate. Or, perhaps the slate is fine and the acid has brought disolved grout grout out of the joints and left it on the stone.
Try using a good deep cleaner (alkaline) and a scrubbing pad to see if you can loosen anything from the surface. If the actual slat eis damaged itslef, then what happens when it is wet? – does the colour come back, at least until it dries out?. It may be possible to use an enhancing sealer on this – provided the slate is not already sealed.
One other thought that ocurs to me, and forgive me, but not eveyone will correctly identify the stone, are you 100% certain the stone is a slate? – it is just that not all slate is sensitive to acids where other stones, like likemsstone for example typically are very sensitive.
If you could sned some pictures I might be able to help more
Hope this helps
Ian
peter | Oct 6, 2011 | Reply
ih ian iv just bort some second hand slates to do my garage roof but when iv looked at them thev got bitumem tar like substance thaks if you can help me to find out how to clean them
taffy | Oct 6, 2011 | Reply
Picked up our Italian honed slate hearth today.
Would appreciate any advise regarding cleaning, and sealing the stone.
Didnt get any advise from the store due to collecting from pickup point at the rear of the building.
Ian Taylor | Oct 12, 2011 | Reply
Hi Peter,
To be honest the only way to chemically remove tar is a strong solvent. First scrape as much of the solid tar off as you can then use a solvent, you could try white spirit or turps etc. to get the residues. It may take several attempts.
Hope this helps
Ian
Ian Taylor | Oct 12, 2011 | Reply
Hi Taffy/Ceri?
I do not know precisely what slate you have but if it is honed then it is smooth so an imprgnating sealer is the way to go. You may or may not want to consider an enhancing sealer – if the slate is at the moment unsealed – (and you may want to check that the factory/supplier has not put anything on it) does it darken a lot when wet? – if so do you prefer it in this darkened state, or natural? If you prefer the darkened state you could use a good enhancing sealer like Enrich n Seal or Enhance n Seal – make sure you want this though as it is not reversible.
If you want the natrual look – just a good quality impregating sealer, if the slate is really dense, you may find a solvent based one easier than a water based, if it is qyite porous (slate varies a lot) then the reverse might be true.
For cleaning, a neutral ph cleaner for routine cleaning, something a little higher in alkalie for heavy, periodic cleaning. If it is just the manufacturing dust/sludge, then some washing up liquid and water might be all you need.
Hope this helps
Ian
Ana | Oct 15, 2011 | Reply
Hi Ian,
i have two slate showers the floors are white with limescale. what do i use to remove limescale. the grey slate looks as though it is starting to flake,the cleaner i used was too acidic.
thanks
Ana
Ian Taylor | Oct 17, 2011 | Reply
Hi Ana,
OK, to be honest, if it is a lime-scale issue, and you have a slate that is not sensitive to acids (nor anything within splash-contact proximity) then an acid was the right thing to use – as long as it was a safe one (i.e. not brick cleaner, hydrochloric etc.).
The acidic cleaner should not be making the slate ‘flake’ – Flaky slates are flaky on their own, and sooner or later they will start to loose any lose flake’s but usually this settles down quite quickly, unless they are really bad. (I have a geologist friend who would argue that some stone, sold as slate is not technically slate at all, but a shale or some other sedimentary rock that has not quite made the full metamorphic change into slate, so it is a much younger rock – the less dense, often more colourful, dusty and flaky slates that we see may fall into this category – nothing wrong with them per se, but they can be more susceptible to flaking).
I would remove any loose flakes, check the rest of the slate is sound then clean the limescale. Use a safe acid (look on the back if they are tile grout haze removers and they contain a percentage of phospohric acid or one of its replacements, it should be fine).
Pre wet the floor, apply the acidic solution (may not have to be neat – remember the stronger the solution, the faster it will work BUT, the more potential damage it can do to the grout joint, so start with say a 5:1 dilution rate). Let it sit for a couple of minutes then scrub with a pad or brush.
Rinse well with clean water, (still scrub a little) to remove the acidic cleaner and any dissolved lime-scale. Dry the slate with a towel/paper towels.
Bear in mind that the lime scale has come from your water, so drying the slate (i.e. removing the water) before it has a chance to dry and leave a deposit of more lime, is a great way to help prevent future build up. Let it air dry and have a look. If necessary repeat. The other thing to watch for is the acidic cleaner etching your grout, if your grout is pigmented, or dark, it may now be significantly lighter in shade (maybe already as you have already used an acid). Acids can bring tiny amounts of dissolved cement out of the grout, the calcium from the grout, reacts with the acid to create calcium phosphate which is a salt – and can look itself like a white, lime-scale deposit – so it in theory it is possible for the actual treatment to remove the lime-scale and replace it (at least partially) with another similar problem (again it is broken down by more acid cleaner) – so clearly rinsing and drying help prevent this.
Once you have got the lime-scale removed, and any flaky bits sorted out, let it dry and you will probably need to re seal (especially if some flakes have come of).
From this point on, make a point of drying the floor, not on every occasion perhaps, but frequently. And then use a milder perhaps citrus based cleaner periodically to keep the lime-scale at bay- again, rinse and dry each time you do this. Also a cream abrasive like Microscrub is a non-acidic alternative for keeping it under control (once the initial build up is addressed) Hope this helps
Ian
Ana | Oct 17, 2011 | Reply
Hello Ian, thanks for the advice, i will try this and seal the tiles. then do regular maintenance.
Ana
lauren | Oct 17, 2011 | Reply
Hi Ian.
I have had 120msq of slate laid throughout my house. Days after it was laid builders marked large areas with plaster and paint which I am finding it difficult to remove. The floor is disappointingly stained and builders have scrubbed certain areas which has made the floor lighter and dull. It is a natural riven slate and also seems to have grout trapped in the groves on some tiles. Obviously it cost a lot of money to buy and lay and I want to know how I can get the colour of the slate looking consistent throughout the house.
Many thanks,
Lauren.
Ian Taylor | Oct 24, 2011 | Reply
Hi Lauren,
The dull areas that the buliders have scrubbed are dull, hopefully because they have only partially cleaned, and have not rinsed well. This means they may have left residues that have now dried on the surface again.
In most cases like this, with a good quality slate it is usual to use some form of proprietory acid-based cleaner. Provided your slate is not acid sensitive, and you have not got a highly pigmented grout, this may be the best thing to try. Try to find a product that is based on phosphoric acid or similar, DO NOT use a brick acid or one based on hydrochloric/muriatic acid as this can do more harm than good.
The phos acid based cleaners are mild and weak, they are already diluted and can be diluted further, they are designed to take small films off the surface whilst doing minimal damage to the surface of the grout itself.
Test the cleaner neat on your slate in an inconspicuous place just to make sure it does not damage the slate. Then do the following:
1. Pre wet the floor with a mop or sponge
2. Mix your cleaner as per instructions – typical dilution maybe 1:5 0r 1:3, apply it to the floor
3. Leave it to dwell for about 3 minutes
4.Scrub with a scrubbing brush or wite pad, you may nees a plastic scraper to get into some of the deeper parts of the texture
5. Pick up the solution with a mop or wet vac
6. Important step: rinse the floor with fresh clean water, mop up
dry the floor with moving air and/or towels
inspect and repeat if neccesary – it may take several goes as you are taking very thin films each time. The trapped grout in the riven texture may need some local neat application of the above.
Hope this helps
Ian
Darlene | Nov 2, 2011 | Reply
Hi there Mr. Slate genius!
Excellent advice I see here and so well put so I’m really hoping you’ll be able to help me
I have my front garden tiled in riven dark grey slate tiles (30cm x 30cm)
Having saved for an age to get new double glazed sash windows put back in the house we also decided to get the front completely cleaned
ie. All the brickwork cleaned and re-pointed.
They tried their best to keep the run-off off the tiles but needless to say the acid used to clean the bricks has bleached the tiles in a lot of places :0(
It’s etched some areas but some, where gaffer tape, was stuck down is fine so the tiles have a 6cm wide line through them in places!
So, basically I have white spotted and patchy tiles on about a quarter of all the tiles.
I had previously sealed with HG Impregnating Sealer but acid being acid it made no difference
Before I start to weep and sand my little fingers to the boney bone could you possibly offer some advice?
Many thanks,
Darlene
Ian Taylor | Nov 4, 2011 | Reply
Hi Darlene,
You may be ok here. First of all, dark riven grey tiles, that you had to save for suggests good quality slate (Welsh, Cornish, Brazilian etc) which to my knowledge is not generally all that acid sensitive. You could have a more shale-like Indian/Chinese type product I suppose and some of them can be more susceptible to etching due to their make up.
However I think a more likely scenario is this: When an acid attacks cement in grout/mortar it kills some of the colour (giving the bleached etched effect) I think you have a residue of the run off that has been left to dry on the surface. Builders and conctractors seem to delight in using acids, that are often to strong (hydrochloric), frequently not diluted to the recommended rates, blasting the problem with their massive acid overkill, then failing to rinse the away the aftermath. I suspect that if you take some more acid (and I mean suitable one, not a brick cleaner so a cement residue remover based on phosphoric acid) dilute it, pre wet the floor, then apply your solution, scrub with a bristle scrubbing brush for a few minsutes then rinse away with clean water – this is a garden so use a hose pipe and clear that acid wash away.
Let it dry and repeat – do this several times, each time taking a tiny thin layer off the tiles, then rinse away again (the risning is the key part – imagine washing your hair with way too much industrial-strength salon shampoo, and not rinsing! – this is what contractors tend to do with acids). You may have to get down on your hands and knees to pay more detailed attention tothe noks and crannies but I am sure you will get there.
I do not think the acid has done anything to the sealer, the HG impregnator, [or any brand] could not have prevented this as it is on top of the sealer. There is a slight chance that the impregnator has not penetrated the very dense slate, just sat on the top, therefore not properly bonded and in this case the acid wash could take some of it off and possibly turn some of it dull/white in which case stripping the sealer may cure the problem. However I think the first situation is morem likely.
Hope this hleps
Ian
tom mcculloch | Nov 9, 2011 | Reply
many thanks for the good advice, i have applied vinegar as a means of bringing the slate to a uniform dull slate grey finish with no signs now of unsightly staining. i do not think there is any trace of the wd 40 left. what steps should i now take to seal the slate i have some filastone plus purchased for some granite sealing just recently would that seal the slate or what would you recommend?
Ian Taylor | Nov 11, 2011 | Reply
Hi Tom,
Well I am not sure I recommend using vinengar! but, if it has worked, I can only asume the WD40 was not deepley embeded in the slate (and that perhaps even soapy water might have removed it).
However, all seems well so just make suire there are no traces of the vinegar left and that it is perectly dry before sealing. I have never used the product you mention but it appears to be an impregnatiung sealer that also enhances. I cannot think why it would not be suitable, but I would just double check witht the supplier.
Hope that helps
Ian
Chris | Nov 13, 2011 | Reply
Hi Ian
I have black slate floor tiles in my bathroom, presumably sealed by previous owner as there is a bottle of sealant left under the sink!
Over time, water from the shower spilling onto the floor has left white marks on the tiles, and I have tried using general detergent and soap powder and using a toothbrush on the tiles, and nothing seems to be removing the white stains.
What can I use to remove the white stains, and how can I make the black slate tiles look ‘clean’ with a sheen?
Many grateful thanks for your advice!
Best wishes
Chris
Clare | Nov 14, 2011 | Reply
I have found your site and hope you can help me!
I have had a grey riven (chinese!) slate laid in my entrance hall and utility room – the tiles were very mixed colours as you would expect. They were sealed properly by the tiler.
We used the cleaner given to us by the tiler and after the first wash a white blotchy, bloom appeared on some of the tiles – it was very noticeable and I asked the tiler to come and look at it.
They stripped some of the tiles as they thought that they were not sealed properly – I am not sure of the product they used but the smell was overpowering in the house (running eyes etc) and they used a scrubbing brush to remove the sealant.
Now the tiles that they treated are very bleached out – one to the point of being silver, and others with white circles on. They are considerably paler than the tiles they left. Some tiles also have a rusty circular marks on. None of the tiles are a uniform colour anymore.
Help! The tiler is saying that the tiles looked like that when he laid them – not true! Will they come back when he reseals them or has damage been done when they removed the sealer?
I would really appreciate your help as I feel we are being fobbed off and I am going to end up with a floor that looks like a mess!
Thanks Ian.
Ian Taylor | Nov 16, 2011 | Reply
Hi Chris,
OK first of all the white marks, most likely to be soapscum or calcium type depostits left behind by the water, or a combination of both. Over time it builds up. Also, on a black slate, white marks show quite easily, so even the smallest traces of minerals can quickly appear to be quite noticeable. My guess is that had you got a limestone floor you may not even see them. Black slate is usually quite dense, given that it has been sealed also I am pretty confident that the white marks are just likely to be on the top and shoule be removable.
You could try a mild abrasive like Microscrub (you can get it on the All For Stone link top right of the site) failing that, the usual route is a very mild acidic cleaner again see AFS – DO NOT USE A BRICK OR HCL BASED ACID. Dilute the cleaner really well (it won’t take much) apply, leave a couple of minutes, then a quick scrub with a white nylon pad, then rinse with clean water. Lastly, dry the area wqith a towel. I would also recomend tis as an ongoing idea, drying the floor before the water splashes can dry and leave behind any deposits.
As for getting it back to a shine, that depends ion a couple things, what the previous owners sealed th efloor with, and what type of surface the slate has. If the slate is very smooth, or if the slate is well sealed with a good impregnator it will be hard to get a coating sealer to lie flat and bond. IF the slate is textured or riven, and if the slate was previously sealed with a coating sealer then you may be able to apply a new one, for example Seal & FInish Low Sheen or similar.
Hope this helps
Ian
Ian Taylor | Nov 16, 2011 | Reply
Hi,
It sounds to me as though the cleaner you were left with was either not suitable for the sealer; partially stripping it on the first wash, or the sealer is not water-safe. After that you say they used a really smelly product to strip the sealer, this sounds like a solvent stripper and from what you describe as being left , I suspect that you have not got damaged tiles, rather damaged sealer: If they applied a coating sealer, and it was quite thick (and shiny) then a stripper may take two or more goes to remove it, the first attempts merely taking a ‘layer’ off the top and leaving some now damaged sealer still to be removed, it is as thought the selaer has been delaminated, a bit like when aged sticky tape is left on a wall then pulled off some weeks/months later, only part of it comes away, leaving a white/dull ‘back’ part behind.
If this is the case, another attempt with the stripper should completely remove it and then, after the floor has been rinsed and dried, it should be back to the pre-sealed state.
Hope this helps
Ian
Darlene | Nov 22, 2011 | Reply
Hi Ian,
So, SO sorry for not thanking you sooner but I thought I’d wait until I’d tried your suggestion
I’ve now tried the cement residue remover but still no joy
I now have a horrible feeling that I have 40 tiles to fine sand by hand!!
It seems to be the only way to remove the white ‘bloom’ and as an electrical sander smooths the lovely roughish surface then I can’t use that either.
So, it’s grab a cushion and every weekend I’ll be sitting out there doing a tile at a time :0|
Really appreciate your help though, it was worth a try
Kind regards
Darlene
Ian Taylor | Nov 28, 2011 | Reply
OK,
you could try an undlited strengh of the same acid, allow it to dwell a bit longer and use a soft wire brush. If when using it neat, you do not see any fizzing, then the acid is not reacing with the cement, (which means it is not doing anything) so you may need to try a solvent (to break down some polymers first)
Feel frre to email me via the site.
Ian
Karen | Nov 30, 2011 | Reply
Ian,
We had a ‘professional’ out yesterday to clean our 15 yr old natural slate tile floor. The tiles had what appeared to be condensation residue from mineral deposits where our humidifier sits in the winter. The floor had not been re-sealed since installation.
The guy used diluted muriatic acid and scrubbed the floor with a wire brush. Now, the entire floor is discolored and there are what appear to be salts in the grout.
He is to return today to apply a ‘shiny’ (his word) sealer. Needless to say we are less than satisfied. We couldn’t believe how badly the floor looked. Other than applying this mystery sealer that ‘might’ work to get rid of the discolorations and restore the color, his suggestions ranged from renting a machine to installing a new floor.
I can send a picture. I don’t know what the original sealer was. We would greatly appreciate your opinion. We should have gone with a company instead of an individual recommended by the tile store.
Regards,
Karen
Ian Taylor | Nov 30, 2011 | Reply
Hi Karen,
Sorry to hear this, I take it from your use of the word muriatic, you are in the USA, in Europe we refer to the acid as hydrchloric – either way, it is nasty stuff and WAY over the top for removal of a little bit of mineral deposits. better to use a phosphoric acid-based cleaner or similar that may need to be used more than one rather than the ‘sledge-hammer to crack a walnut’ approach of muriatic.
Depening on the type of slate you have, and its mineral composition, you may have suffered some permanant damage/etching – hard to say from email alone. (If you have really bad etching you may have to call on a stone floor professional to see about having the floor re-ground/re-finished)
Regarding the salts in the grout – probably true; I’ll preface this by stating that I am NOT a chemist but basically if you react an acid with an alkalie, (base) you tend to get a salt, plus carbon dioxide and water as the result.
In the case of Muriatic on grout – we are essentially dealing with hydrochloric acid and cement, or mainly calcium carbonate (alkaline) – by exposing the calcium carbonate to the muriatic we get water, CO2 and a salt called calcium-chloride. The salt is harmless enough but, we have replaced some of the cement in the grout (which holds it together) with a salt, (which does nothing). So we have degraded the structure and integrity of the grout, possibly leading to premature cracking and erosion. the salts will wash out with a mild, and far less destructive diluted phosphoric wash but they will leave holes. Also the etching process has roughened up the surface, which has the optical effect of lightening the colour of the grout (rough surface scatters light like the saw-cut face of a stone Vs a polished one).
The etching may tone down over time with use and washing etc but it may take a while.
I would ask if, when wet, the floor (slate and grout) looks better or even acceptable, if it does then the proposed coating sealer MAY help, at least a little – only a test in an inconspicuos area will tell, but my advice is to not let him off the hook in terms of responsibility until you have thoroughly tested this. If wetting does improve the look then you may be better with a good enhancing selaer, in the USA, you could use Enrich n Seal by Aqua Mix ( I would call their tech services and explain) it is an excellent product for this and will darken the slate and the grout. however it is NOT SHINY, if you want a gloss you will have to go the coating sealer route, you cannot add a gloss to the Enrich n Seal route – (it is such a good sealer that no coating will sit on it correctly)
Hope that was some help
Ian
Karen | Nov 30, 2011 | Reply
Ian,
Thanks so much for your well informed and immediate response! Yes, we are in the US. Yes, the floor looks better/probably acceptable when wet with water. We are not looking for a shiny finish. I don’t know the type of slate but it does have a rough (natural) finish.
We are allowing him to come out and test a small area behind where the fridge sits this morning.
As a note, after reading your posts I ran into the kitchen only to discover the finish on my relatively new KitchenAid stainless steel mixing bowl and the stainless steel tray on our kitchen scale is permanently damaged from the fumes.
I would definitely consider the etching on the tile ‘really bad’. It appears in the ‘grain’ of every tile. The grout isn’t so bad, only a few places that are white which were previously dark gray.
Thank you again for your time and for sharing your knowledge.
Karen
Karen | Nov 30, 2011 | Reply
Ian,
I thought it worth posting that we may have solved the problem. Our guy brought a bottle of TileLab Heavy-Duty Cleaner Stripper. Before applying it we called the company and based on our info they recommended applying it full strength to a test area and waiting 15 minutes before using a scrubber then sponging it up with a clean, wet sponge. So far, it looks like it is working beautifully.
The problem: WAX! And by figuring this out and by not charging us for yesterday’s work and product, he redeemed himself.
Apparently, years ago the floor was heavily waxed. The product is working much like a wood finish stripper. We can see the wax sort of bubbling up off the surface.
Also, our guy brought with him a bottle of Aqua Mix Enhancer (seeing that also restored our confidence) as well as Stonetech Impregnator Pro Sealer.
After reading your response to the pinned forum post, ‘Slate- Sealer Disaster, advice needed urgently’ and I have a question. Given this is a high traffic kitchen floor, the main entry into the house and mud/snow/ everything room, would you recommend the coating over the impregnator?
Thank you,
Karen
Ian Taylor | Nov 30, 2011 | Reply
Hi Karen,
Thanks for coming back with this – it great to have a happy ending!
Wax! – OK, well it is hard to second guess what has gone on in the past sometimes. Well the Tile lab should do a good job of removing it, might need two goes plus make sure he rinses it WELL and then dries it.
As for the enhacning sealer – if it is your intention to use thisn then DO NOT try to put a coating sealer on top – if using the enhancer it is a case of using it on it’s own, and furthermore the floor must be bone dry before you do it. Even with the other impregnator, you will find that a coating sealer may not want to bond on top – so it is either or, depending on whether you want a gloss finish ir not, bear in mind also, that a coating sealer will require more frequent maintenance and reapplication.
As for redeeming himself, what about your stainless-steelwork?
Glad it worked out
Ian
Karen | Nov 30, 2011 | Reply
Thanks, Ian. I’ll go with the impregnator. He is definitely getting his money’s worth out of his knee pads and he’s gone through at least 40 gallons of water!
He offered to polish the stainless “or whatever I can do to make it right”. He is busting it so hard right now that I hesitate to bring it up again until he’s done.
Happy to refer any and all who have an interest in stone/tile to your site.
Take care,
Karen
Ian Taylor | Nov 30, 2011 | Reply
Hi Karen,
Great news, sounds like he is a hard working, reliable guy, just made an honest mistake (happens to all of us), cudos to him for seeing it through, and to you for giving him the chance.
take care
Ian
Tracey | Dec 27, 2011 | Reply
Hi
Wondering if you could help. We have had a stove fitted with a smooth slate hearth. A bottle of red wine has been dropped on the hearth and where it has spilt the slate has gone a paler colour to the rest of the hearth. It was cleaned straight away with washing up liquid and water. After reading the rest of your blogs I think it may have been etched??
Many thanks
Tracey
Ian Taylor | Dec 30, 2011 | Reply
Hi Tracy,
Many slates are not known for their susceptibility to acid etching, but some of course can etch. So yes it is possible that the acid in th wine has etched the colour and made it a little lighter. If the surfacce feels a little more dull or powdery than the parts that remain ok, then that is another sign of etching. Also, some slates have components that are not 100% ‘fixed’ in the stone, so colour pigment could be mobile – meaning that with a concentrated cleaner, or an acidic liquid like the wine, could strip out some of the colour.
It is hard to say without seeing it, but it may get better over time. You may be able to use fine sand paper/emery paper with a little water (wet & dry paper and gently blend the etches back into somthing close to the rest of the slate.
It may be possible that an enhancng sealer could darken the patches down again and make everything look more even, provided the slate has never been sealed with anything previously. If the slate looks ‘nice when wet’ then this may be something to consider.
Hope this helps
Ian
Karen Stevens | Jan 4, 2012 | Reply
Hi
Great site but my mind is doing overtime on what to do.
I have grey slate flooring in the kitchen (Homebase), which was laid approx 6 years ago. It has never been sealed, and has been fine up until now. It now has a few water marks and in general is looking a bit dull. I was wondering which product would be best to use for a deep all over clean (floor area 10′x 18′).
Thanking you in advance for any advice.
Karen
Ian Taylor | Jan 6, 2012 | Reply
Hi Karwen,
this sounds like a standard periodic deep clean is allthat is needed. Over time slate will get grubby, and I suspect that 90% of the lack-lustre look is dowmn to a build up of the tiniest traces of both dirt and detergent residue that has built up a ‘patina’ over the last 6 years.
Use a good high alkaline cleaner like heavy Duty Tile & Grout Cleaner (see All for Stone ad on right). Pre wet the floor, then mix your cleaner say 4:1 with warm water, apply it to the floor and leave it for 15 minutes, without allowing it to dry out. Scrub, EXTRACT (mop or wet vac) RINSE – with clean water, and extract that, lastly polish dry with an old towel.
At this pount if both the slate and the grout joints have come up clean, when dry, you may consider a sealer.
Hope this helps
Ian
Emma W | Jan 15, 2012 | Reply
Wow chuffed i stumbled across this page, you sound very knowledgeable.
Ok so here goes…..
We have just been given an old slate bed of a snooker table, we are going to use this as a fire hearth. I would like to try and bring it to a darker colour as it is light grey. Do you have any suggestions as what we can use to
: Clean it
: Buff/Polish
: Darken
:Seal it
Thank you very much for your time
Ian Taylor | Jan 16, 2012 | Reply
Hi Emma, lucky you!
Having never removed the felt off a snooker table I do not know what may be on the slate, but expect it was glued down with somthing so there may be residues of a glue. Try a least aggressive to most aggressive approach.
First try the least aggressive/most gentle method and if that does not work, move up to somthing a bit more aggressive.
So, I would first just try a mild soapy detergent – like washing up liquid with plenty of water, and a WHITE scrub pad the type for scouring dishes (often white nylon pad on green sponge?) DON’T use the GREEN scourers as they are a bit more coarse.
if this does not clean it, then use a high alkaline detergent instead, if that does not work, then you may have to go to a stripper like Sealer and Adhesive Remover. (see All for Stone opposite).
When well rinsed and dry you can look to seal. Notice when cleaning it, if the wetting action made it go much darker, and darker in a desirable way. If so and this is the effect you want, then look to an enhancing sealer (such as Enrich n Seal), make sure the slate is 100% dry before you apply it, and do not leve it looking wet – even if you like the look of it, apply the enrich n seal to a dry stone, leave it to penetrate for 5 to 10 minutes then buff dry to leave a matt finish.
Give this a few days to fully cure, you will not be able to put a gloss coat on top but you could apply a buffing polish like ‘Brilliance’
hope this helps
Ian
Sue | Jan 19, 2012 | Reply
Hi Ian,Glad to have found your helpful site. We have just purchased from the reclaimation yard a piece of slate for a hearth. It looks to have been a previous hearth and has some rust stains and gloss paint marks which we hope to remove! Do you have any ideas for cleaning please and sealing.
Many thanks
Sue.
Sharon | Jan 19, 2012 | Reply
Hi Ian,
We have an en-suite shower made from black slate tiles. It was proffessionally done, sealed, grouted etc.
We ended up renting our house out and the previous tenants didn’t seem so particular about cleaning. We now have what looks like limescale covering all the tiles (it’s a grey appearance). We have tried limescale cleaners but had no joy, is there anyway we can paint the tiles back to black and then re-seal them?
Thank you for your help.
Sharon
Ian Taylor | Jan 23, 2012 | Reply
Hi Sue,,
OK, for rust typically go for a very mild phosphoric acid type cleaner, use dilute with water, may take several applications. Only other thing to say is that this is usually effective only for surface rust deposits (rust that has been left on the surface) should you have rust from within the stone due to minerals contained in the slate, then this may not be easy or even possible to remove.
For paint, use a spaint stripper or solvent if it is thick and stubborn.
Having said that often paint is relatively ‘new’ as a contaminant, so may be on top of a layer of general dirt and so may well come off with a normal deep clean (it comes away with the dirt that it is stuck to)
What do yo have most of? – paint, rust, genral dirt? – if it is just in need of a general deep clean, with a few spots of rust and paint, then go for an alkaline cleaner, you may well find the rust and paint come off duinrg the cleaning process, particularly if you boost the cleaner with Microscrub. If not then tackle them in isolation afterwards.
If you need them here is a list of suitable products, avaiable from All For Stone (click link: http://www.allforstone.co.uk/default.asp?)
1. Heavy Duty Tile & Grout Cleaner
2. Microscrub
3. Phosphoric acid Cleaner/substitute (or Exrtreme for really bad rust)
4. Seal & Coating Remover (powerful but safe solvent)
for sealing, I am guessing that the surface is smooth, or honed. In which case avoid a coating sealer, use an impregnator that leaves no surface coating. Choose either a no-colour natural sealer or an enhancing sealer if you wish to permanatly bring out the colour
Hope this helps
Ian
Ian Taylor | Jan 23, 2012 | Reply
Hi Sharon,
Limescale (and soap-scum) can indeed leave a greyish depositi on the slate. The good news is that it is on the slate and therefore should come off, leaving the real slate behind. Unless, it is acid damage to the actual slate but I am guessing this is less likely.
The limecale removers you may have tried are probably acids, they work by reacting with and disolving the mineral deposit, but they have to be used correctly: leave on the slate for a short period, not long, usually a few minutes, do not allow them to dry out, scrub with a scrub pad, then the all important part, RINSE well with cleanwater. then I would dry them down with a towel.
ON NO ACCOUNT TRY TO USE ANYTHING STRONGER LIKE A BRICK ACID OR HCL
the acids used for this are often, Phosphoric, Citric or sulfamic. These are relatively weak in solutions that are available to the public and that may mean several applications. In deed thick layers of limescale may look worse after one slight cleane, or even a couple of inccorrectly executed ones, as the acid may have a) been left to dry (and thus not achieved much) b) reacted with the limecale and produced a halrmless slat as a by product, which is now also ontop of the slate or c) has removed say half or a third of the deposit, like taking only one layer of skin away with dermabrasion etc, so additional cleans, done properly with the right product may well help follow my procedure below for this:
1. pre wet the slate with plain water (stops acid from drying to quickly, keeps it at the surface)
2. mix correct solution of limecale remover (or use Phosphoric ACid Cleaner) as per ionstructions, apply to slate. walls may need you to keep reapplying it due to the efffects of gravity, use a spray bottle
3. leave for a few minuts, keep wet with more solution
4. scrubb hard for several minutes
5. RINSE WELL WITH FRESH WATER – easy in a shower.
6. Dry walls with towels – removes all water and any traces of calcium or other deposits tha may be in the water.
7. inspect when dry and repeat if required.
Hope this hlpes, as far as sealing goes, if they have been presealed, then I suggest topping up with the original sealer if possilbe
Cheers
Ian
Sue | Jan 26, 2012 | Reply
Thanks Ian, we will give it a try.
Morag | Jan 26, 2012 | Reply
Hi Ian,
I hope that you can help me. Last year we purchased a black Caithness slate hearth. It was left in our garden for a number of months while we renovated and unfortunately it has now turned predominately brown. Any ideas on how we can restore it back to the original colour?
Many thanks,
Morag
Ian Taylor | Jan 27, 2012 | Reply
Hi Morag,
Just incase it is this simple, try a good scrub with a mild detergent, or with the tiniest bit of bleach in water (try a very small test spot) I am just thinking that if it has been out in the damp, it is is possible that it has just got coated with some brown mildew or algea type organism.
However, it could also be oxidisation (i.e. rust). From what I understand, Caithness stone is actually a kind of siltstone, rather than a slate, they are both very similar types of rock and contain simmilar clays/silts etc and the minerals that often go with them.
It is quite possible that some form of iron mineral is present. If there is a lot of iron present, then inside the stone, away from moisture and air, it will stay fine, but when a new surface is exposed (in other words when the slate is cut and polished or finished) some fresh iron may be exposed. As it has been outside in the rain and got wet for long periods, there has been ample time for the iron to react with the water and oygen in the air, so it begins to oxize, producing the ‘rust’ colour.
You may have some success with a very mild phosphoric based acid cleaner – suggest (pending results of first test above) that you try to get some Phosphoric acid cleaner from All for Stone or similar. Use dilute on pre-wetted stone, agitate andrinse, then dry off
Hope this helps
Ian
Liz | Feb 1, 2012 | Reply
Ian, We recently had a black slate floor installed. It was sealed at the time of installation. The coloration was inspected and found to be fairly uniform. A couple of months later, while the house was still under construction, metallic gold deposits suddenly appeared on a number of the tiles. The deposits were random and appeared in more than one location on the floor. The deposits have a different (rougher) texture than the rest of the tile and it looks like something spilled, but the installer says it’s a natural part of the stone. Have you ever heard of natural metallic deposits suddenly appearing in sealed slate? Thanks for your thoughts.
Dawn Clarke | Feb 1, 2012 | Reply
Hi Ian,
can you recommend a slate cleaner brand? I can’t seem to find any floor cleaner that expicitly says is suitable for slate and have ran out of the cleaner we were given when the floor was laid.
We have slate flooring in our entrance hall, utility and kitchen as we were advised by our builder that it was extremely durable.
I’ve unfortunately found it quite difficult to keep clean (even though it was sealed twice) and it doesn’t seem to matter how much I clean, but the floor still looks dull with persistent marks. Do you have any advise on how to tackle this?
Many thanks,
Dawn
Ian Taylor | Feb 6, 2012 | Reply
Hi Liz, those natural metalic deposits sound like rust – and yes it is very common.
Two possible reasons, one is somewhat more obvious to spot, and that is simply somthing above the slate that is rusty, like a metal bucket, maybe a haning basket made of metal that has water drippig from it, some other fixture or fitting that is rusting and is either in contact with the floor itself, or has water coming fro it that is.
The other and perhaps more common situation is that minerals within the slate itself are oxidising. Slate is made up of many original components like clay, and these can contain minerals, and sources of iron in one form or another. When the slate is first cut and finished into tiles, a new, fresh split face is exposed. Up to this point that part of the slate was ‘inside’ the stone, not exposed to oxygen and moisture
Now the slate face has been exposed to both, and any hitherto invisible iron-bearing mineral, has been allowed to react with water and air, the moisture can come from above – cleaning and washing, or from below (rising moisture, most slates are pretty impervious so moisture travelling up through them from below is less likely), or from installation, there is a lot of water in grout, and maybe moisture from the sealant?
So any number of reason but, often slates like this will simply react with the ambient moisture within the air over time, and so this I think is the most likely explanation – the iron-bearing minerals, now exposed, have over a small period of time begon to oxidise or rust -hence the colour and rough feeling.
Much of this will rub off, and you could reduce it with a little dilute phosphoric acid cleaner – but it may come back over time, however each time you clean it it may reduce in intensity and take longer t come back. You may or may not eradicate it completely. It is however a natural occurance with this type of stone, just like sap coming out of pine, or wood fading or yellowing over time.
Hope this helps
Ian
Ian Taylor | Feb 6, 2012 | Reply
Hi Dawn,
One of the reasons that you won’t find a dedicated ‘slate seaerl’ is that most stones can be treated with similar cleaners and slate is usually pretty resillient stuff.
Look for a general mild, neutral cleaner that says it is ok for tiles and stone for regular cleaning.
Apart from that, use a mild to medium alkaline cleaner like Xtreme Clean by All For Stonefor deeper cleaning.
Try to avoid acid based cleaners.
The dullness you report may be a reulst of the original sealer wearing down -this is normal for coating sealers, or it could be a build up of detergent, leaving a patina, normally fixed by giving the floor a good deep clean with an alkaline cleaner then rinsing well with water and even rubbing it dry with towels.
If you had a coating sealer (one that was on top of the slate, that maybe had a sloght sheen to it) and this has worn (through alkaline cleaners and/or wear from foot traffic) then this would account for the dulling and the makrs (as the sealer has gone, so to has the stain protetction) – a good deep clean as detailed above then reseal should fix it. From then on try to use neutral or mild cleaners rethat than alkaline for every day use.
If it was an impregnating sealer then again it may have diminished a bit so again, deep clean and top up the sealer when done.
Hope this helps, if you have further questions please feel free to ask, if cou could tel more about the sealer used that may help
Ian