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Cleaning Slate – Expert Advice on Cleaning Slate and Slate Floors – Part 1

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 one based on phosphoric acid. Beware though as any acid cleaner may etch the grout also.

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: either an impregnating sealer which will give you a natural look with a mat finish and below surface stain protection. Or, if you prefer the look of wet slate, in so far as the darker colours, but still want a natural, mat, no-sheen finish, then look a good quality enhancing sealer such as Enhance ‘N’ Seal. Alternatively you can use a coating sealer 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, we recommend using a high alkaline cleaner. More in Part 2.

Update 22/01/13 – Check out this case study on cleaning slate

 

 

 

Copyright Ian Taylor and The Tile and Stone Blog.co.uk, 2013. See copyright notice above.

40 Comments

  1. Hi

    I have just bought a slate hearth that’s untreated with a natural Matt finish. I think someone has accidentally but a bowl on the hearth and now there are some ring marks. I have tried warm water and soap but the marks are still there. Do you have any advice?

    Also, do you recommend a sealant as we are going to be having an open fire on it but I don’t want it to loose the natural Matt finish.

    Thanks!!

  2. Hi Ian,

    I have water marks on a slate hearth. The slate hearth was inherited so I have no idea if the slate was sealed or treated with anything.

    Would Wd40 remove the water marks? What other things could I try?

    Thanks,
    Angela

  3. Hi Angela, apologies for the late reply I have been away. Water marks normally mean some kind of deposit, whatever minerals were dissolved in the water at the time (for example often in hard water areas the water contains calcium and it is this calcium that is left behind as the water evaporates).

    the usual remedy is a mild acidic cleaner which will break down most mineral contaminants – so worth a try – use a cleaner for grout haze based on say phosphoric acid, (no need to go for a brick acid). It ca be diluted also and should not harm most slates- do a small test first though.

    WD40 is just a thin oil, all it will do, an on a temporary basis only, is darken the slate, this MAY or MAYNOT ‘mask’ the white marks.

    If the white marks are not a deposit and are instead a damaged area, then some kind of enhancer may help hide them but there are better products designed for this other than WD40.

    hope this helps

    Ian

  4. Hi Jennifer,

    OK well it may depend on what caused the ring in the first place. If it is a mineral based deposit then a mild, phosphoric acid based cleaner may help, but you could try a mild abrasive cleaner such as Microscrub (one of my all for stone products available on Amazon) – or an alkaline cleaner may be needed – you may have to test a few different things.

    As far as sealing is concerned, to keep the matt finish you need an impregnator (a sealer that sits below the surface) most slate though is very dense, and will not take much sealer. With impregnators there are two choices: 1) a natural look (no colour change, keeps the matt finish and the natural look of the stone) or 2) An enhancer – a sealer that is designed to have a matt finish but darkens and enriches the colour of the stone – gives a wet look if you like – this is usually a non-reversible process. I have both of these types of product available but there are several brands on the market.please feel free to contact me by the contact page if you would like further information.

    Hope this helps

    Ian

  5. Hi,

    We have had new black thick slates in our front garden but only after a few weeks we have brown marks (rusty coulour) appearing and growing bigger. We are told this is natural to the slate! We are surprised we were not told before. How can we get rid of it.
    I am not sure if our slates have been sealed or not.

    Also we have had Indian sand stone tiles in the back garden. Looked great for a few days then we have constant layer of white coat of top that is not going away. Plus we have now mastic from builders that we are still trying to brush away. Have you got a suggestion for cleaning and getting back to original colour?
    Claire

  6. Hi Claire,

    OK there are a few things there

    Let’s start with rust on the slate. Two ways rust can get on slate, from above, have you got any steel or metal pot stands, hanging baskets or other items that may be dripping rusty water onto the surface? If so then you have rust deposits ON THE SURFACE – which can be easier to remove. The other way, and this is what they mean by natural for slate, is that some slate can have iron-bearing minerals within the make up of the stone. This may have lain dormant while the stone was underground but now that it has been cut, and therefore exposed to the elements, you can find that any free iron can oxidize and form essentially, rust spots – this is quite common in some slates.

    Again if this is happening at the surface of the stone then you have at least a fighting chance of removing or at least diminishing the spots. If the slate has been sealed then it may be harder as the sealer will now protect the slate, and the rust from any attempt to clean them however, you need to try a phosphoric acid based cleaner (don’t go for a standard brick cleaner based on hydrochloric) I have one but there are several brands out there, often labelled as cement or grout residue removers – if you need more help on this message me via the contact page.

    For the sandstone – not sure what could be turning it white but two suggestions: 1) Sealer – some sealers for this type of stone are affected by moisture when they have just been applied (in other words if they got wet or even damp before they fully cured) – only way to deal with this is to strip it off with a sealer stripper – but you can do a small test with a solvent like nail varnish remover – if it removes it then it points to this being the issue. Or, 2) Efflorescence, the movement of soluble minerals, often salts, from beneath the surface, in the presence of water: this can come from the stone, the grout, the bedding material or the sub floor, or a combination of all of them. As the water moves through to the surface, it evaporates leaving behind a fine layer of say, calcium salts, (but it can be other things) this leaves a white/grey film at the surface, sometimes it can be more crystalline and even light and fluffy – but sometimes a cloudy film. Try the same phos acid based cleaner on this – if it works then it points efflorescence.

    As far as the mastic is concerned, if you mean silicone or acrylic or polyurethane type mastics then some kind of solvent may be required, but it may be a very difficult job. If you mean a cement based mortar pointing then this might be treated withthe same acid cleaner

    Hope this helps

    Ian

  7. We have a slate floor in front of our fireplace. My son likes to play near it all the time and now there are white marks where he usually places his feet. I’ve tried warm water and dish soap and slate cleaner, but I can’t seem to remove these marks. Our home was built 3 years ago so I’m not sure if they put sealer on it when it was installed. How can I remove these marks? Thank you!

  8. Hi, well I suppose, the only thing a child’s feet can leave on a slate would be small traces of perspiration, which contain among other things, salts and minerals. I doubt there is any serious damage ( and I also doubt he is stripping any sealer off!). I would first try something acidic, even vinegar, just try a little to see if it removes the white marks, it should not harm either the slate or a sealer if there is one.

    Let me know if this works

    Ian

  9. Hi,
    My son split a small glass of vinegar on the black slate hearth of my fireplace. Now I have a large spot and not sure what to do. Got any suggestions?
    Thanks.

  10. HI, Hmm, vinegar has left a mark, is the ,mark a dirty stain, or a lighter mark like an etch? Many slates are not affected by acids in this way, so I am hoping it is a stain, in which case try an alkaline cleaner

    Can you send me a pic?

    Ian

  11. My husband spilled a small amount of alcohol on our dark slate floor. Now I have a large white spot and not sure how to remove. Got any suggestions?
    Thanks.

  12. Hi,

    OK, you are not specific on the type of alcohol, but if it is wine then it can be acidic. Usually, white marks tend to indicate acid etching. In the case of dark slate this is not normally a problem as a lot of the older, darker slates (like Welsh slate for example) are not really sensitive to acids.

    Some of the younger ones may be though, a little. This can result in the acidic compound slightly etching (dissolving and removing the finer particles at the surface to leave a rougher surface, which reflects light in a different way, hence less colorful appearance, it can sometimes even feel less smooth to the touch if really bad.)

    Does the white mark disappear, albeit temporarily when you wet it? – this can also indicate etching.

    Sometimes it can be removal of colour pigmentation – anything that is mobile in the slate can be effective washed or etched out.

    The other possibility would be some kind of stain/deposit left on the surface, this would not tend to disappear when wet.

    If it is colour loss due to etching, you may be able to get a colour enhancing sealer (provided the rest of the slate has not already been sealed) or, it might be possible to use fine wet and dry emery paper to rub the surface and improve the colour – worth a try.

    If it is a stain or deposit, some kind of cleaner may well remove it, try an alkaline cleaner, and or a microabrasive cleaner (containing calcium or similar non scratching abrasive)

    Hope this helps

    Ian

  13. Greetings – I just spilled a bottle of methylated spirits all over my dark grey slate floors. The whole floor is splattered with white splashes and spots. I assume the methylated spirits stripped some kind of protective coating (the slate is matte finish) I tried cleaning it with white spirit but it has no effect. The spots and splashes have not diminished at all. Any other suggestions please (other than calling a professional).

    Many thanks!

  14. HI,

    OK, it does sound like some kind of coating has been stripped – do you know what the coating was? – can you go back to the oringinol supplier/installer and ask? Then you might be able to just cover up the spots to a pretty good standard locally.

    Might be that you have to use a stripper to remove all of it and start again

    Kind regards

    Ian

  15. Hi
    We have slate tiles in our shower. When we clean the taps (chrome) we use a bathroom cleaner and try not to let any of it get on the slate. Over time though some obviously has and it has left pale ‘run marks’ down the slate and white areas in the grain.
    Is there any way we can get rid of these and stop it happening again in the future?

  16. Hi,

    OK, I suspect that the cleaner is acidic in nature, designed to dissolve things like hard water marks, soap scum etc. It will do this, and, also it will dissolve fine particles from the grout between the slate tiles, not enough to cause any damage really but the cleaner will then carry the dissolved particles and then when it runs down the wall, and the liquid evaporates, the particles are deposited on the slate.

    You could try using the same cleaner directly onto the slate, where the runs are. Try pre wetting the area first then spray the cleaner on, leave a couple of minutes, then scrub with a nylon scrub p[ad or scrubbing brush (a nail brush even)

    Then rinse with clean water immediately.

    IF this does not work you may have to try a slightly stronger acidic cleaner designed for grout haze removal.

    This should help remove the problem but it will not prevent it from re occurring

    The best way to help prevent re occurrence is to clean your taps in the normal way, then, make sure that you immediately rinse the slate down after wards, before the cleaner ha a chance to dry

    Hope this helps

    Ian

  17. I have a black slate on my fireplace hearth. In trying to remove stains, I have used a diluted CLR. It has left white stains which are very unsightly! The home-improvement store recommended cleaning it with xylene and then using an enhancer and polisher. Do you think that will work? You seem to know a lot about Stone tile.

  18. Hi,

    OK, well first of all that product (if I have identified it correctly) has about 3 different acids in the ingredients, and the manufacturers do state that it should NOT be used on any natural stone. Diluting the CLR does not do much other than reduce the amount of those acids you are putting on the stone.

    Acids react with minerals, in your case most likely any calcium in the cement in the grout joints between the slate. There may even have been traces of cement and therefore calcium on the surface of the slate. This reacts with the acids to form various salts of calcium, these then crystallize or form as a grey/white powder or deposit when the water and other liquids dry off – hence the white stains you have. Also, even if there was no cement to react with, the acids themselves could dry as a powder in the texture or surface of the slate – especially if no or inadequate rinsing was carried out.

    Just occasionally there are some slates that themselves have mineral content that can react with acidic cleaners – this is usually the brightly coloured ones – I would try to check this out with your slate retailer first.

    As for Xylene – that is a smelly solvent and while it may do something for certain types of stain or contaminants, it will do nothing on mineral deposits – I have no idea why the home improvement store suggested it for your situation.

    I suggest you try, in a small controlled test, re -applying the CLR – this time to break down the deposits that it left behind, but do it like this:

    1. Pre wet the the area with water – this keeps the cleaner at the surface and prevents it drying into the stone
    2. Apply more CLR – try it dilute to begin with, reduce the dilution to make it stronger if needed
    3. Scrub the area with a scrub brush
    4. Rinse away IMMEDIATELY with fresh water – this is to carry away the the material you just dissolved, rather than leave it to form on the surface again
    5. Let the test area dry and evaluate, if it has done nothing – try a stronger cleaner like a grout haze remover (based on something like phosphoric acid, NOT muriatic) if it has worked but not 100%, then repeat the process and re evaluate. If it has worked then go ahead and continue over the whole of the affected area.

    Once you have it clean (and dry) you can then evaluate whether or not to use an enhancer – this would make it look permanently dark, a bit like how it looks when wet. Only do this of a) you like the look, or b) you are unable to effect a clean, as it might mask the marks.

    One last word of caution, if your slate has been previously sealed with any other sealer, then an enhancer may not work (this may be why the retailer suggested the Xylene? – to remove any old sealer? – even so, it is not always possible to remove all traces of previous sealer and this can cause an enhancer to be deployed unevenly, resulting in a permanent, patchy appearance).

    Hope this helps

    Ian

  19. My mum spilt apple cider vinegar all over my slate kitchen floor and it has lightened the area where the worst of the spill was. Please can you tell me if I am going to be able to get rid of it? The slate is normally fairly shiny like it has a sealant. The area where the spill was is now very dull. Rented property so a total nightmare and in the centre of the floor!

  20. Hi,

    OK, Hard to say but it could be 1 of 3 things:

    1) Slate has no surface seal and the cider-vinegar has left an etch mark – the acid has basically eaten away some of the finer particles in the slate’s surface
    2) There was a coating sealer and the vinegar has stripped/dulled it
    3) The vinegar has left a dull residue on the surface – try scrubbing with a souring pad and some soapy water – does anything happen?

    From what you say I am guessing it is most likely to be #2 – in which case a quick clean and if you can find out fro the property owner (rented?) what sealer was used, just top that up locally – i.e. just on the affected slate.

    If it is acid etching etching then it may be possible to re finish the stone, depending on what type of slate it is and what finish it has, but you may need to get a stone restoration professional for that

    Hope this helps

    Kind regards
    Ian

  21. Thank you so much for getting back to me. I will try 3 and then work backwards! You have been a great help. At least I know it is probably fixable!
    Best wishes, Sally

  22. Hello
    I’ve just come across this great blog while searching for help on stains in slate!
    I have a polished black slate hearth in front if my fireplace. I imagine pretty standard with installations now. I noticed some round pale grey splash marks on the hearth, a cluster of about 6 each around size of 10p piece. Initially I thought it was wax that might have dripped from a taper I use to light candles. It doesn’t seem to be but maybe I removed wax at the time and this is a resultant stain. It makes most sense to me that this what it would be.
    I would like to know if there is a way of darkening these spots to blend better with rest of hearth?
    Thank you,
    Clare

  23. Hi Clare,

    OK, it could be wax residue if so, a god alkaline de-greaser may help shift them.

    However some slates (this is quite common in Welsh slate) have inherent green or grey spots that are simply just part of the stone. Either way darkening it down may not really work. Do they darken sufficiently when you wet the slate just with water?

    If so then it might be worth trying an enhacning sealer but you will have to make sure that there is no trace of another other sealer on the stone in order to be able to use it.

    Hope this helps

    Ian

  24. Dear Ian,

    You may be my last hope. We have a beautiful grey, matt finish slate hearth. It was purchased and cut & polished new only last year. It was treated with Lithofin Stain Stop and then LTP Stone Oil (by me before we started to use the stove) with but it seems that some drips from the glass cleaner (HG interior Stove Glass Cleaner) we use have left white drip marks on the slate. I’ve tried washing up liquid and hot water and when it’s wet, it looks better but you can still see the marks. I’m reluctant to try anything stronger without professional advise. I’d be very grateful for any suggestions.
    kind regards
    Glenys

  25. Hi I suspect that the glass cleaner has some solvent in it and that is may have partially removed some of your sealer and oil. IF you thin about it, something that is powerful enough to cut through soot and backed on dirt is going to make light work of a sealer and oil.

    Also as you have out the sealer on a dense stone like slate, it will be very well protected against staining – so even the oil to applied after the sealer will not have really got in too deep.

    You may find that only the loosely adhering oil has been removed and so you could try just wiping over the spots with a little more oil will mask the spots and cover them up again -worth a try. If not you may have to go to the more extreme solution of stripping back the seaelr and oil and starting again

    Hope this helps
    Ian

  26. Hello
    I have slate tiles in my bathroom and kitchen. The ones in the bathroom are particularly discoloured so as we are in a hard water area I am guessing it is the limescale as the marks are white – well it actually looks like a chalky colour all over the tile now.
    What is the best product for me to buy please to remove the marks? I have tried Viakal limescale remover but it hasn’t made any difference.

    Thank you

    Claire

  27. HI,

    Assuming that the tiles have got like this over time, I would agree it is limescale plus possibly soap scum also. I have not tried viakal but would expect it to contain an acidic cleaner – maybe it is not as strong as you could get with a specialist cleaner

    look for a cleaner based on phosphoric acid from a tile store and do a test first – do not got to the extreme of a brick cleaning acid though

    Also, if the limescale is stubborn and has built up, it may take more than one go to remove it all

    Pre wet the surface then apply the cleaner at the recommend dilution, leave for a few minutes, scrub with a nylon scrub pad, then rinse, repeat if requied

    hope this helps

    Ian

  28. By the way I do have a cleaner that may help, but I am not really set up to sell it in small quantities, and as it is an acidic cleaner it would cost more for me to ship than the product costs.

    Lookout for HG Blue Limescale remover or HG Extra – grout cement remover – my competition but hey ho

    Like you blog by the way

    Ian

  29. Hi,

    I just installed slate stone veneers on my 2 story fireplace/chimney. It’s a darker grey slate color and on random pieces of the stone there is a white corrosion build up that I can wipe away with a wet sponge and for a few days it looks fine but then it starts to build up again. Is there away to keep it from coming back? Also those pieces seem to be flaking too almost as if the corrosion is rotting the stone. Can this be stopped?

  30. Hi Brad, this sounds like a form of efflorescence: the white stuff you are seeing is a mineral (often just labelled salt, but it can one of several minerals). Basically there is some soluble mineral, in the ‘system’ this can be in the stone itself, or, in the concrete/brick behind, the setting material or the grout – or any combination of those. The addition of moisture, most likely from the installation materials, can dissolve the soluble minerals and then as the moisture comes out of the installation, at the surface, sometimes even through the stone etc, then it starts to evaporate, as it evaporates, it has to leave behind the soluble minerals it pick up along the way, so they (the minerals) drop out of solution and form little crystals and so you see this white deposit at the surface.

    Can they be causing the flaking? – well maybe, but the slate most likely has those weak cleavage planes to begin with, if the mineral-laden moisture can get into the stone and the crystals start to grow there, then in theory they could lever off the flakes as the crystals develop – or contribute to it anyway.

    The good news is that it won’t continue forever, there will be a finite ‘reservoir’ of these soluble materials and when they are gone they are gone, no more for the moisture to collect on its way through. Also, if this is internal, and not exposed to the elements (like if rain were pouring down the chimney, but given your location I doubt that is an issue) then the moisture responsible for this is just the installation moisture – which is also finite and will finish drying out soon. As soon as the moisture source has dried up, you will see no more efflorescence, even if the system is still loaded with minerals as it will have no vehicle to move it to the surface.

    There are treatments out there but most are acid based and while they can quickly dissolve the white stuff they will also etch and damage, to some degree the mortar/grout etc – as long as you can wipe it away then you should not need this.

    Hope this helps

    Ian

  31. Ian, very helpful, thank you.

  32. Hi

    This is a great thread. My husband cleaned our kitchen slate floor with bleach. One side is ok as it had water tipped over it but the other half has got white marks all over it. What would you recommend to clean it with. When it is wet it doesn’t have the white marks
    Thank you

  33. Hi Sam,

    OK, logically it seems to me that the undiluted bleach has damaged something – not the slate though , most likely it has damaged whatever was on the slate, whether that is just a build up of contamination or a sealer of some kind, or a bit of both.

    If you had a sealer on there then the concentrated bleach may have irreparably damaged it, partially stripped it, but not 100%, what is left is a residue of the sealer – a bit like when clear tape is left to age on a wall and then you try to remove it and you pull it apart leaving an opaque residue – breaking down a coating on stone can be the same, the stripper, in this case the bleach has done half a job and stripped the surface of the coating. If this has occurred then you need to completely strip the coating, with a proprietary stripper, then re seal with an appropriate sealer.

    If however it is not damaged sealer then it is most likely to be a build up of ‘dirt’ – a patina of the years of grime and any polishes etc that have built up on the surface and again the concentrated bleach has partially cut through this layer. If so you need to clean the floor with a high alkaline degreaser – but no bleach, until is is all removed evenly.

    If the sate is relatively soft and was very colourful, (autumn colours, browns, yellows and reds etc) then it is possible that the bleach has bleached some of the actual colour from the stone. It may have etched the surface slightly, as wetting out with water appears to restore the colour, albeit temporarily, then it might be possible to use an enhancing sealer to do the same as the water but permanently. However I would rule out the firts two scenarios first, clean it thoroughly and let it dry out before making a judgement.

    Hope this helps
    Ian.

  34. Hi Ian,

    How are you?
    We recently moved to our new place, that had served as a rental for some years.
    The new place has a large slate floor area through hallway and kitchen /dining.
    After close inspection this was build up with large amounts of dirt and grime.
    For a big clean I scrubbed the floor with a mixture of baking soda and vinegar.
    It definitely has really cleaned the tiles and grout.
    After washing it of with mild detergent and warm water the dried floor has white markings on it. They mostly disappear when wet but once dry re appear.
    I think that the vinegar may have been too harsh. The floor was not shiny before and I do not believe that it was sealed.
    I think its a 30yr old floor, it has mixed colour, greys and oranges.
    Just wanted to check if I need to clean it with something else, or can use an enhancer to restore the natural colours?
    Appreciate your assistance!
    Kim

  35. Hi Kim

    Sorry you are having these issues, I must say I despair sometimes at these home made remedies – they can help of course; ‘granny’ used them for years and swore by them I know but, we have better solutions now, and a better understanding of cleaning issues in general. The problem is that if we don’t fully understand what the cleaner/household solution is doing then we can get into trouble.

    OK, the acetic in the vinegar can, to some degree clean grease and grime (but it is nowhere near as effective as its chemical opposite – an alkaline solution). The baking soda reacts with the vinegar and one of the things it creates is CO2 – as a gas – you see this in the form of bubbles.

    So, the acid does some mild cleaning, the bubbles help a little by creating some lift and movement. Combined with the general wetting from the water in the vinegar and the mechanical scrubbing, then of course you will get some cleaning.

    However, essentially the acetic acid in the vinegar reacts with the baking soda – meaning that they kind of neutralize each other (thus making an already not very effective cleaner, even less so) – but, apart from CO2 and a bit of water, the reaction also creates a salt – Sodium acetate. It is this, the sodium acetate, the by-product of the acid/soda reaction that is most likely the cause of the white film that now coats your slate. Sodium acetate is water soluble and will absorb water and turn translucent and also dissolve in water which is why when you wet it, it seems to seems to disappear – only to reappear when it dries out – this is because the water evaporates and so the dissolved sodium acetate reforms again as it is left behind.

    OK, first try washing it away again, even with just water, but buff the floor dry – do not allow it to just air dry as explained above, if while it is wet, (and therefore the SA is dissolved) you then remove the water and take the SA with it. Worth a try, it may take several goes, with the white marks diminishing each time until it is all gone.

    You may find that over time it just gets walked off anyway.

    Once it is clean and dry you can then investigate sealing – an enhancer would bring out the colour BUT you will have to absolutely certain that there is no previous sealer as traces of old sealer can prevent an enhancer from working correctly, leaving to a partly enhanced floor with a very un-satisfactory patchy appearance.

    Hope this helps

    Ian

  36. Hi Ian,

    I would really appreciate your help?

    We have a fairly large slab of black slate that our gas fire sits on. I don’t know if it was ever treated when new, but I’m assuming not?

    Some years ago when the room was decorated, it got covered with a fine layer of white dust from rubbing down paint and filler. The decorator tried to get the dust off with water and a mop.

    Ever since the slate has lost its black sheen and is paler in appearance and has a lot of white patches in the rough ridge areas of the slate, where the dust seems to have collected more? I am assuming that the dust has penetrated or been washed into the surface of the slate itself as we have never been able to get it out no matter what we have tried.

    Your advice would greatly be appreciated.

    Simon

  37. Hello I hope you can help . We have untreated Caithness slate floors with underfloor central heating. The surface is not smooth. In dry areas it looks as if salts have emerged and the pitted surface is speckled with a chalky substance. That’s ok. But in the bathroom particularly the shower area the effect is much more pronounced and the slate has become very discoloured and is a nasty yellowing colour in places . Nothing seems to make it look clean again. Any advice.

  38. Hi Sorry I seem to have missed this. I don’t think that dried paint dust and filler will penetrate and actually stain slate, but it can stick to it and bond, and get caught in any micro texture. I think I would try a very mild acidic cleaner – one designed for removing grout haze, usually based on phosphoric acid – not a brick cleaner, and use this diluted, apply, let it sit for a minute or two then scrub with a nylon scrubbing brush. Then rinse off with lean water and buff it dry with an old terry towel or similar. That will hopefully remove the powder contamination but it may still be dull after (cleaning it with any thing may have taken some of any treatment tat may have been applied – lot of fire place installers/sellers use old methods like oil based treatments to leave a bit of a finish on the stone, it is possible that cleaning efforts, including what you have done already, will strip off some of that. IF you can find out what they used you could re apply some afterwards

    Hope that helps
    Ian

  39. Hi,

    OK the stone from Caithness is actually a calcareous siltstone (it goes under the generic label of ‘slate’ but is not geologically speaking, actually slate) this does not matter, it is a great stone, I mention it as there is a degree of calcium in its make up. This might mean that using an acidic cleaner is not the best thing to do (a phosphoric acid cleaner would be my go to choice here otherwise). On their tech sheet Caithness say that the stone can suffer slight discoloration and delamination when immersed in acid – but that is total immersion and it does not state what acid or what strength, or how long. A mild phosphoric acid based cleaner, used very dilute – MIGHT be OK here but you might want to call Caithness and verify that with them – I would certainly make sure I conduct a test first – on a spare tile if possible.

    The risk is that an acid could attack the calcium carbonate components withing the stone’s matrix – what happens is it eats away at the fine calcium particles, and this ‘etches’ the stone, depending on how much there is, and how much the stone’s colour comes from that mineral. The net result is a roughening up of the texture of the the stone (I suspect that would not be noticeable here) but that also leads to a lightening of the colour – so the BIG danger is that far from removing white marks, you actually create more and can reduce the colour from black to a washed out grey.

    If you cannot go this route you could try a micro-abrasive cream cleaner cleaner, there are several out there I have one in my range, message me via the contact us page if you would like details. They work by gently abrading the surface, or at least the contaminants, the abrasive contained within the cleaner is it self calcium based and so it will not scratch the stone.

    Hope this helps

    Ian

  40. thanks for this informative answer Ian . I’ll message you now.

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