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Tile and Stone Maintenance

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, 2013. See copyright notice above.


  1. I just bought a house and the oversized shower has colored slate on walls and floor of shower. The floor is made up of tiny (1 inch x 2 inch) tiles and it is 8′ x 10′. This house has been sitting a long time and in the corners of the shower, it looks dirty, but looks more like white chaulky stuff that is convering up the tiles (kind of gritty too). What can I use to make it look like the tiles in the middle of the shower? They are the ones that get wet and get used and look clean. Thanks!!!

  2. Steve,

    Thank you very much, you are a star! Your advice worked perfectly. We wont be using a steam cleaner on the floor again.



  3. It sounds like you have a very mild case of efflorescence. You might be able to remove this with some light abrasive, try some cream abrasive cleaner (nanoscrub if you are in the USA). I have written extensively before on efflorescence so I won’t cover that again, but if the slate is not acid sensitive, you may find that a very dilute wash with a MILD grout haze acid based cleaner (NOT A BRICK ACID or MURIATCI/HCL) will work wonders – DO A TEST first in an part of the shower where it does not matter too much if that is possible, but in any case PRE wet the tiles, the apply a small amount of your cleaning solution after diluting it considerable, leave it a few minutes then scrub, then rinse.

    Now dry the area with a towel and then let it air dry. Hopefully it will work without bleaching away any colour from the slate (or the grout) but this depends on the correct dilution (start at say 10:1 water to cleaner, if it does not work, try 7:1 etc).

    If it is efflorescence you may find that it comes back, treat it straight away with just the nanoscrub and you should be fine. Check also (once clean to your satisfaction) that there is adequate sealer on the slate as this will help prevent more moisture getting in (one of the causes of efflorescence).

    it could also be that you have got cement/grout left on those tiles – well the same remedy as above is what I would try, just might require several goes.

    Hope this helps

  4. We have a smooth, green, slate hearth which has been stained by a shaving brush containing shaving foam and water being left on it, leaving a white circular mark. We would very much appreciate your advice on how we might be able to remove this stain. Thank you.

  5. Hi,

    We have dark grey ceramic floor tiles in our newly refurbished bathroom, however the builder has stained them with concrete used to build a glass block wall. Since that, when the ceiling was drilled for a new spotlight, more staining has appeared (assume from ceiling dust).
    Can we use the same acid as for the slate you’ve mentioned above?


  6. Hi Lorraine,

    I have written a post on this here

    I suspect you have an oily stain, read the entire post or skip to the paragraph after step 3 whee I talk about using a poultice. It mentions a product that is no longer available in the UK but there are alternatives such as Poultice Pro (available from Tilinglogistics on 0121 705 5333)

    Hope this helps


  7. Hi Kelly,

    I would say this sounds fairly straight forward. You have cement deposits and plaster dust etc – yes a regular mild acid based cleaner for removing grout haze should be fine. Again I stress not to use a brick acid or one based on Hydrochloric acid.

    Just be 100% sure your tiles are glazed and not with a metallic glaze (they are not an faux metal effect, bronze, platinum etc) – if you have a spare tile in storage, just make sure that the cleaner does not damage them.

    You may need several applications – this is fine, be patient it is designed to take small amounts at a time so as to minimize damage to grout joints.

    Hope this helps


  8. Hi, I live in a 1950’s house in Kent (hard water!) All our internal windowsills are slate tiles, cemented in. Over the years they have gotten paint splats over them (matt and satin wall paint) and what look like water stains. I don’t know if they were ever sealed, they are smooth tiles and mostly matt, although in less used areas they look a little bit more polished. I would love to restore them to their former glory, but I’m on a tight budget. I have stovax slate cleaner and polisher which I applied the other day – they look a little darker and slighty shinier, but no cleaner!
    Thank you!

  9. Hi Charlotte,

    I think (not 100% sure) that the product you have used is more of a maintenance cleaner, and more of a dressing/polish than a cleaner – I am sure it will contain a small trace of wax or oil or similar and this has the effect of slightly darkening the colour and adding a bit of a sheen. I would suggest this could be used after you have got the slate clean – just like using Pledge or Mr Sheen on a wood table.

    To clean the paint splashes you need a solvent, a paint stripper I would suggest perhaps a clear spirit like white spirits, be careful some like turps are a bit oily in nature themselves. The solvent will also remove the cleaner you have put on.

    For removing cement stains you will need an acidic cleaner – get a MILD one from a tile shop, not a brick acid or anything based on HCL.

    Once you have got the slate clean, rinse it well with water and allow it to dry thoroughly. At this point try reapplying your slate cleaner to ‘dress’ them

    Hope this helps


  10. HI

    I have a slate foyer floor that I had sealed many years ago and has stood up wonderfully. Recently I had my rugs cleaned and the tech dripped some solution all over my slate foyer as they were carrying out the equipment. Now I have more than 50 spots from the drips as they walked through the foyer. It took of the sealer in those spots. I have a call into the company but they had to speak to the tech first. I do not know what kind of solution was dripped on it… does anyone know what I need to do ? DO I have to have all the sealer stripped from the floor and resealed? Any suggestions.? Thanks…

  11. Hi Linda,

    OK, this is hard to say from just a message like this but I am thinking it could be one of a couple of things.

    First though, you do not say what type of sealer, coating or impregnating? If a coating and it has lasted many years without intervention – then I am surprised. Before I go on, just check that they have not simply dropped dirty water from their machines and this has left a dull deposit on top of your slate, that is giving the appearance of the seal having gone.

    OK, the logical first thought is that they dripped something alkaline/solvent-based and that this has stripped the sealer. If this is the case, then, basically the sealer in those spots is not gone – so needs replacing. Whether or not you can simply top up the sealer in those spots is debatable – do you know what the original sealer was? do you still have any? if a coating sealer the rest will have worn and so just adding new to the spots won’t look right. My suspicion is that the whole floor will need to be stripped after all this time, and a new seal applied – need not be a huge job though.

    The other possibility here is that things are not what they seem; If the floor was sealed many years ago (and your comment seems to infer that no further top up or repeat sealing has occurred) then I sincerely doubt that a topical/coating sealer was used as it would have long since gone,even an impregnator may no longer be 100% present and effective after all that time. What may have happened is that over the years, with were and traffic, and regular cleaning, the seal, may have slowly degenerated/been worn off, but it was not noticeable as at the same time, a ‘patina’ has been built up – the patina comes from, and there is no nice way of putting this, a mixture of small traces of dirt building up with residues of the cleaning solution that is used, all slowly building up and being ‘polished’ by time and foot traffic into basically a natural coating. To be honest this can look quite nice and give a pleasing effect – a floor that has ‘aged’ nicely if you like. It is just possible that the cleaning solution dripped by your carpet cleaners has cleaned off this patina – so in fact the spots are ‘clean spots’.

    Again in the last scenario, there is only one solution and that is to apply a deep clean to the whole floor – and strip back to the slate surface, to be fair if you have had many years without need of deep cleaning you have done very well. Once you clean it back you will have a choice of ways to reseal/finish the floor.

    Hope this helps


  12. Ian,
    Thanks for your response.
    I thought it was just a coating sealer. ( I could be wrong). I did wash the slate 2 times after they left thinking it was dirty water.

    I just now found out from the company whos tech spilled that it was cleaning solution . They will be stripping and resealing it. At their cost.

    thanks again for your response.

  13. I have a shower which was tiled in with glazed porcelan tiles, glass tiles, slates tiles and granite. There is no way to isolate any one type of tile to clean and I am not sure what is safe to use on all 4 different types of materials. What cleaner can I safely use on all materials to get rid of soap scum buildup?

  14. Hi Joanne,

    OK, as you have probably deduced, the ‘usual’ treatment for soap scum is a mild acidic cleaner that is designed for such a job, but you are correct to check whether your materials are capable of resisting damage from such cleaners. First of all the glazed porcelain and the glass should have no issues (apart from in some rare cases where there is a metalic glaze) also most slate is resistant to acid cleaners, some of the multi coloured Asian or African slates cna lose a little bit of colour as sometimes the rusty iron deposits (that provide the colour) may be reduced in intensity, but most native US, UK and other European slates (greys, greens, blacks and reds etc) tend to be pretty resistant. Similarly most granites are also acid resistant. However there are some stones sold under the umbrella term ‘granite. which are in fact geologically speaking, not actually granites, (such as basalts) some of these can etch with acidic cleaners.

    So, as with all the advice I give, TEST FIRST – if you have a spare tile for each type, try leaving some neat cleaner (we are talking about mild acid cleaners based on phosphoric or equivalent, not HCL) on them for 5 to 10 minutes. Then rinse away and allow to dry. If no damage, then you will certainly be safe at normal use strength).

    I would also try a cream micro abrasive cleaner like nanoscrub in the USA, or Microscrub in the UK.

    Hope this helps


  15. Hello, I have old rabbit urine stains on my floor, I have washed it repeatedly and when wet it returns to original colour but dries white and terrible looking. Please help. Thank you.

  16. Hi Karen,

    OK, this is a bit different, I take it that we are talking about a slate floor? don’t know which kind of slate though. There are two potential things to be concerned about, an actual stain (discoloration left by a contaminant) an etching – physical damage to the surface of the stone by acidic/corrosive compounds.

    Stains from urine ought to be reasonably easy to remove with alkaline detergent or even bleach (diluted) but an etch would leave a permanently damaged surface. This damage (which can affect a few but not all slate types) dulls the surface, by etching away finer particles, leaving the surface changed in colour and flat and lifeless, with the surface often a little rougher to the touch. When wet this temporarily disappears as the water evens out the surface and alters how the light is reflected. when it dries out the effect is lost and the dullness is returned.

    If this is the case, then either the slate surface must be restored (may be possible with fine sand paper, or diamond hand pads – unless the slate surface was riven) or if no other sealer has been used, then a colour-enhancing sealer may help.

    It would help me if you could send a picture or two

    Hope this helps


  17. Hi there,

    I have a similar problem to Julia above. I actually used a natural acid based anti limescale bathroom cleaner on my kitchen cupboard doors and the drips from the product have left splat marks on my natural slate floor. It looks like it has almost bleached it slightly as they marks are lighter coloured. I tried the solution you suggested for Julia by that has not worked. I wonder can you suggest anything else. I thought of applying some left over sealing product to them as that did take the slate a shade darker?
    Any help would be very much appreciated.
    Thank you in advance

  18. Dear Ian,

    My tenants have recently left the slate hearth of my fireplace covered in what are obviously large splodges from using a household clear on it. Is there any way this can be repaired?

    Many thanks for any assitance.

  19. Hi Lesley, it sounds more like you have etched the slate than left deposits, so using more of the cleaner on the slate is not a good idea (assuming this is what you mean about trying the same remedy as Julia).

    Etching removes some of the surface of the stone, not all slate will do this but some will. You cannot get that missing stone back, your idea about using the darkening effect of your sealer may certain help, (the sealer will need topping up on the etches in any case) so well worth a try.

    failing that you may need to get the slate re finished, if the spots are only small, you could try rubbing with some fine emery paper and a little water

    Hope this helps


  20. Hi Sam,

    It depends on whether the marks are stains or etches. If they are stains, then I need to know what they are, but it sounds more like damage (etching) from a potentially acidic cleaner. This might not be repairable – you may need ot get the stone surface refinished.

    If they are oily marks from some kind of polish then you could try an alkaline cleaner.

    Hope this helps

    if you can provide any more information I may be able to help more


  21. Hi Ian, I tried to read through all your comments hoping to find a similar situation to mine. I bought an early 50’s mid century modern home with black large different sized smooth slate floors having up to an inch grout based on the odd sizes. It would be gorgeous if it’d been cared for. I seriously doubt anything has ever been done to it other than moped and obviously waxed over the years and as a result is very dull and dirty looking, especially all the edges. Again, I think a build up of ‘old school’ wax and grime over the years. I need a turbo cleaning product hopefully by name if you have any recommendations they are much appreciated.

    The same room has stacked stone pillars and walls floor to ceiling and it looks like wax buildup has been splashed onto those over time also. Could the same cleaner above be used on them also? None of my materials are new, they are all original to the home built in 1951.

  22. Hi Marty,

    I would use my normal procedure of starting with an alkaline cleaner first, if this is not sufficient, try adding a micro abrasive. In some cases a stripper would be required, it all depends on how much build up there is.

    As you are in the USA, try Aqua Mix Heavy Duty Tile & Grout Cleaner in conjunction with nanoscrub or equivalent. You should be able to use the same on the walls too.

    Hope this helps


  23. Hi
    I have just finished laying a grey/green honed slate floor in the Kitchen.
    After a party at the weekend i now have lots of small white marks all clustered together in certain areas, I dont think it is a spillage, it seems more like stiletto heel marks and the tile does feel like it has indentation, I know its difficult for you to say without seeing but do you think the marks could be polished out with fine wet/dry paper, if i wet the tile the mark does not fully disappear so I think just a liquid polish will not work.

    Any Ideas

  24. I hope that you can answer this question for me. My only shower is out of commission until I find out what to do.

    The shower is finished with 12 x 12 black slate tile. It was looking grey and tired so after trying some spray on tile and grout cleaner with no success I stripped whatever sealer there might have been using Aquamix Sealer & Coating Remover. When I stripped the tile there was no apparent residue. However the lower back wall and adjacent corner of the shower turned a blotchy, very light grey color as if it was very dry.

    Twenty four hours after stripping I began sealing the tile with Aqua Mix Enrich & Seal in the hope that when it was absorbed by the slate the grey would turn black. I sealed most of the shower and it looks great except for the area that I mentioned above. I stopped before sealing the back wall because it was apparent that the grey was not going away in the adjacent corner.

    I have stripped and re-finished quite a bit of this material in our condo in the past but have never run into this problem before.

    What should I do now? If I seal the back wall it will look terrible forever or until I paint it or something. Perhaps some Grecian formula? Should I try stripping this area again? Help!

  25. Hi Chris,

    I think you have partly answered your own question. It does sound like heel marks I have seen this a lot. The darker the slate, the more white the marks appear. basically it is the rough edges of the tiny little crater that was created by the heels that have not had time to soften. Over time (quite quickly) the stark, white edges will rub back to become less notieable (and will eventually look like the do when wet, so still there as actual stone has been removed/scratched/impacted etc) but they will start to blend in. This is akin to the same ting in real wood floors – over time they get pock marked to heck but it is accepted as ‘ageing’ – slate will not suffer quite as badly as the wood.

    you could certainly try a little wet & dry – no harm it might take the edge off the marks a little. If the slate has been sealed, and was sealed with a colour enhancing sealer, try dabbing a tiny bit more sealer on the spots then rubbing the surplus off and buffing with a soft cloth.

    What you cannot do is completely remove the marks, not with out resurfacing the whole floor – and that means grinding which is just not a practical solution.

    Hope this helps


  26. Hi Jerry,

    I think I know what this is.

    Whatever sealer was on before, was a bit thicker than you have experienced to date, or the Stripper was not allowed to dwell for long enough.

    That stripper is a great product, but it needs time to work – up to an hour. What I believe has happened is that for some reason (either the sealer was thicker there or you used a slower dwell time on that section) the stripper has only done half a job.

    It has broken the sealer down, take the surface off it if you like, killing the shine and transparency, turning the remains of the sealer dull, opaque and greyish-white. The solution is simple, re apply more stripper, let it dwell for longer, keep wetting it with more stripper, and scrub hard then rinse really well with a mild soapy solution (this just helps remove all the stripper). Polish it dry with a towel, then let it dry naturally -you are just going back to finish the job it started.

    I have reservations about using Enrich n Seal over stone that has been previous;y sealed, even it is has been well stripped, but if you hare getting good result son the other walls then there is nothing to suggest you wont on this wall, once it is fully stripped.

    Hope this helps


  27. Ian,
    As you suggested it seems that I had not removed all of the old sealer before applying the new Enrich & Seal. I had to go through three circuits of stripping the shower until I was confident that all the sealer, both new and old, was gone. That was truly a hellish experience which I never wish to repeat! The fumes were brutal. I don’t usually bother with a respirator but I sure did on this project. Yesterday I applied the new Enrich & Seal and the black slate tile positively sparkles. That was a hard lesson learned but at least the final result was good.
    Thanks for your help. I really not think that there was any old sealer left and would probably have tried some other, completely wrong approach.

  28. Hello, I wonder if you can give me some advice please. We have purchased some old smooth slate slabs recovered from an old school and want to use them as a hearth for our woodburner. The slabs are coated with a varnish finish. Could you advise how best to remove this varnish please? Also we would like to darken the appearance of the slate a little, can you recommend a product to both seal and darken the slate leaving a mid sheen finish? Thankyou for your help. Kind regards, Annette 🙂

  29. Hi Annette,

    You will need a good paint or varnish remover for that, you could try a sealer stripper but depending on the thickness of the varnish it might take a few goes.

    As for darkening it after, provided you get it completely clean/stripped then you could try an enhancing sealer, like Enhance n Seal by All for Stone

    Hope this helps


  30. Thankyou Ian for your advice which is so much appreciated 🙂

  31. Hi there. Fabulous, useful site – and I wish I’d read it a few days ago!
    I’ve just had some beautiful multiple- coloured slates laid in my hearth. They’re not smooth. The stove installer is coming tomorrow and I told him I’d seal the slates myself this weekend before he comes. I had an unopened bottle of Plasplug Tile Sealer (suitable for slate, stone etc), bought years ago. I’ve given the slates three coats, following instructions to the letter. They look fine, but I was hoping for a soft sheen, to bring the colours out more. This hasn’t happened and the slates still look matt. On the bottle, it recommends using Plasplugs Marble & Slate Clean & Shine but it’s no longer available. So, my question is… Can you please advise what I should use to give the desired sheen to the slates?
    Thank you very much for your help.

  32. Hi Sue, you really needed a coating sealer, there are several on the market, but they may not work now as they need some porosity to bond. That porosity will now be greatly reduced due to the impregnating sealer you have used so you may need to strip that out first

    Hope this helps

  33. Thanks very much for your help. I have given it a coat of Lithofin Slate-Seal and it seems to have done the trick – the hearth now has a lovely soft sheen. Thankfully there was no need to strip out the sealer! Thanks again.

  34. Hi there,

    I tiled a kitchen floor, (8m2) 6 weeks ago using black slate tiles 300×300. Done the usual as ive tiled dozens of slate floors over the years. Once tiled, ive thoroughly cleaned tiles before grouting. Grout washed off, and tiles left to dry overnight. So next day, i sealed the floor, and to enhance the ‘black’.

    I returned next day, to see that the slate floor, was looking good, apart from a dozen tiles that werent so ‘dark’ or ‘black’ as the majority. So i thought maybe seal these ones again.

    However a few days later, these dozen or so tiles, look awful. They look cloudy grey/whitesh colour. The affected tiles are dotted around the floor, not just one area. Where as the good tiles, look jet black. Why the difference ?….they all been treated the same.

    Im at a loss, to why this has happened. Ive ask several other tilers, and been to tile shops for advice, but nothing… answer.



  35. Hi Ian, just looking for some advice on cleaning a slate floor. I laid a square tiled grey slate floor, uniform in colour throughout, with an uneven surface to it, in our kitchen and dining area about six years ago. At the time, I only gave it one coat of sealer, and over time the floor has started to look a bit dull and dirty and regular mopping just doesn,t seem to do much. The grout as well is also looking pretty dirty and stained. I was wondering what product you would recommend that could give it a proper clean, maybe take away the weathered seal and just generally a really good clean, and also any tips for doing this. Also what new sealant would you recommend putting on when finished cleaning. Would appreciate any help you can offer. Thanks, Robert

  36. Hi Lee, first of all you don’t say what type of sealer you have used; was it a coating sealer or an impregnating sealer? If impregnating, was it a natural one or a sealer designed to enhance the colours?. The kind of issues you are describing suggest a couple of possibilities.

    First of all, if the sealer has darkened the tiles then it sounds like you used either a topical coating or an enhancing impregnating sealer. One reason some tiles go dark and not others (esp with the latter) is if there had been any other sealer present before, thus stopping the sealer from getting in and doing it’s job. However as this was a new floor I do not think this as likely.

    The other issue, and it can be a big issue with enhancing sealers and topical sealers, is too much moisture before sealing. I note you say you left it over night, frankly this could be your problem. many sealers of this type will need the floor to be almost completely dry – overnight is often no where near enough – even if the floor ‘looks’ dry and even if you have done hundreds like this and never had a problem (that is more by good luck than good judgement I am afraid). If there was sufficient moisture left in the floor (and it could have been in the grout joints) then these type of sealers can take in some of that surplus moisture and it permanently affects the way they cure. This can get worse over a few days as it finishes curing, so more tiles can be affected on day two than on day one etc.

    I cannot be certain, but I am leaning towards too much moisture as your explanation,. I suggest you get onto the tech department of which ever sealer you used for a recommended solution – If I am right, the sooner you react the better, unfortunately I was away over the weekend and did not see this until now.

    Hope this helps


  37. A few questions there Robert. First of all, it sounds like the floor is ready for a deep clean, with something like Xtreme Clean by All for Stone – a high alkaline. Given what is left of your existing sealer, this may well all come off with the deep clean. f not, you may have to use a sealer stripper.

    AS far as re sealing there are lots of choices available, you may not get the opportunity to use an enhancing sealer though as the floor has been sealed before and this presents a bit of a risk that you wont get even coverage and penetration, resulting in a patchy appearance.

    You could go for a coating sealer, given you have a textured finish, I would guess you had something similar before, the are easy to apply and can last a year or so before they dull down and need replacing.

    Hope this helps


  38. Hi Ian,
    I’ve had a browse through all of he posts and you certainly seem to know your stuff but I couldn’t quite find an answer to my tile problem!

    In my en-suite both the walls and floor are covered in what I believe to be slate tiles. They are matt, slightly contoured and a beige / sand colour. I have been cleaning them with floor wipes such as Dettol (not sure if the chemicals in these are the problem) and they now have dark grey spots all over them – it looks a bit like stars in a night sky, however it has only happened on the floor, the walls are absolutely fine even though I’ve used a bathroom cleaner on them.

    I would like to find a way to remove the marks if possible, any help would be greatly appreciated. Was going to send a picture but being a bit blonde and couldn’t see where to attach!

    Many thanks,

  39. Hi, I have just had slate kitchen floor tiles fitted, I have two problems the first is that I haven’t been able to seal the floor as cannot remove the grout residue and the second is that my delightful children spilt apple juice and didn’t tell me until it had left an almighty stain – how do I remove both to prepare for sealing? Thanks in advance nx

  40. Hi Nuala,

    OK, the grout residue that is caught in the ridges, generally needs a mild (SAFE acidic cleaner – DO NOT USE one based on hydrochloric acid – this means most brick acids. Look for one that claims to be based on phosphoric acid. Use in accordance with the instructions, but basically pre-wet the floor.apply the dilute cleaner, leave it for a few minutes, then scrub with a nylon scrubbing brush, an old tooth brush, or something that can get into the texture. Rinse well and repeat – it may take several goes to get through it safely, without doing damage to the grout in the joints).

    You may find that some of the apple juice stains come out as a result of the above but if not, you will need to switch to an alkaline cleaner such as All for Stone Xtreme Clean. Or even a poultice.

    Hope this helps


  41. Hi,

    I have just had a pale grey and rust slate hearth fitted, the fitter has oiled it and now it is black. Will it dry to the original colour?



  42. Hi Louise,

    I think it depends on the oil but, quite possibly no. If it was going to return to its original colour I think it would have done so by now.

    The oil is acting like a colour enhancing sealer it is leaving behind some solids that affect the way light is reflecting back from the slate, the same thing happens with water, but of course water evaporates out and leaves it as it was, so when dry the colour goes back to how it was.

    Unlike an enhancing sealer though, a good alkaline/degreaser should be able to remove it, you could then use a clear, water-based sealer to seal the slate if needed and this should not alter the colour

    Hope this helps


  43. Hi Ian thanks so much for the help, think I may have been too late tho as even after cleaning with heavy duty cleaner I sealed it and now it looks awful :0( I obviously did something wrong as have permanent water marks and general dullness over the tiles – I may have to start again – could you please recommend something to remove the sealant I put down (i used diall from local DIY shop) and then a cleaner and sealer that will do the job – thanks so much Nuala x

  44. Hi Nuala,

    did you clean the grout residue off with an acidic cleaner as per my suggestion, as you only refer to an alkaline one? – did you do this before sealing.

    You can use a stripper to remove the sealer – might be best to call the company who’s sealer you used for their recommendation for a stripper.

    if you get the sealer off, then you may still need to do a acid clean, as per my original advice, to remove any grout residue.

    Regarding the water marks, any chance you can email me some pics?

    hope this helps


  45. Hi Ian,

    I have some kind of black slate or sandstone(??)hearth at the base of my decorative gas fireplace. I foolishly tried to clean pet urine off of it with vinegar, and now I’m afraid I may have etched it as it has a greyish white area where the vinegar was. Either that or I stripped the sealant? Can you please tell me how to tell for sure what I am dealing with and how to possibly repair the etch myself or reseal it? When I wipe with water, it restores the black color until it dries again, so perhaps there is hope? I can send a photo if that helps, but I don’t know where to send it. Thanks so much!


  46. Hi Ian,
    We have just acquired a home that has a 1000 sq. ft. room that is entirely floored in slate. I don’t think it was ever sealed, as it appears dull. The former occupants evidently allowed dogs to live in the room, and there is an HORRIFIC odor (dog excrement and just plain dog smell). I have tried scrubbing with white vinegar, spic n span, pine sol, and plain soap and water to no avail. Every time I scrub, the smell gets stronger. Is there anything at all I can do to remove the odor? I think because it appears unsealed, the odor is deep into the porous slate. Thank you so much!

  47. Hi, my daughter sprayed anti bacterial cleaner on our black tectured slate fireplace. As soon as i noticed i washed it with water but the slate has white streaks that i cant remove. Any advice would be appreciated.

  48. Hi Jennifer,

    If it is black, I would be more inclined to believe it is slate (although it could be other similar stones like mudstones/silt stones etc)

    It does sound more like etching to me than removal of sealant, although if you had an impregnating (below surface) sealer, then some sealer may have been removed at the same time. Had you a coating sealer (visible low sheen or glossy coating) then I doubt you would have removed it with vinegar, and you would not have an etch either.

    The problem temporarily disappears with wetting as the water evens out the surface (which was made rougher by etching) and gives a flat, reflective surface (more like the flatter, smoother surface that existed before etching), as the water evaporates however, the effect fades and the etch mark appears to return.

    If it is etching, then you may be able to use an enhancing sealer to do the same thing that water does, but permanently. However, it may darken that part of the slate more than the rest, if there is still a good amount of old sealer in the rest of the stone, then this may look odd (the enhancer will not get into the stone over the other sealer, only in the etched part).

    If you slate surface was polished, or very finely honed, then the etch may also be quite rough to the touch, by compassion, if this is the case then you might be better having the surface re-finished, perhaps by a local stone professional. You could perhaps try yourselves with diamond hand pads – I don’t have time to go into that here but you may need several grades and you would have to do the whole surface, and re seal afterwards

    I hope this has been of some help, you can send me pictures – use the contact us page on the blog to send me a message and I will reply, you can then send me some pics back to that email


  49. Hi Elizabeth,

    I think you have got it about right, I am no chemist but I think there is a ‘reservoir’ of the time-absorbed contaminants and you are bringing it out bit by bit, also re wetting the dry contaminant may be reactivating it, and allowing the odours to come to the fore.

    Logic says that eventually this will diminish and stop – the reservoir of contamination will be finite.

    Having said that i don’t think anything acid based (your vinegar) is going to help, these contaminants are best treated with a high alkaline cleaner, there are many on the market, especially in your part of the world.

    I suggest you conduct a deep clean with a high alkaline cleaner, follow on bottle instructions but essentially:

    1. pre wet the floor
    2. apply the cleaner
    3. leave it to dwell for 15 minutes DO NOT ALLOW IT TO DRY OUT – keep adding more if it does
    4. scrub the floor, and particularly the grout joints
    5. remove the dirty cleaning solutiojn – preferably with a wet vac if you can get one, if not with a mop
    6. rinse well – this means CLEAN water, applied to the floor, SCRUBBED a little with a CLEAN mop, then extracted again
    7. RINSE again – repeat step 6 to be double sure – also makes sure there is no detergent left to build up

    allow to dry, ventilate the rooms and see what the smell is like after that – try to be subjective – is the smell gone, still there but not as bad (in which case repeat all of the above – because it is working) or is it worse – in which case repeat the above because it is working – it is bringing the bad stuff out and to the top

    this may take several attempts, but the above process is by far the most efficient –

    if the odour is really bad, you may have to consider using bleach for one of the cleans, then rinse and clean as described as above

    once you are happy you can find a suitable sealer

    Hope this helps


  50. Hi Lesley,

    Difficult to know exactly what has happened here, but it could be that there was some kind of sealer/coating or polish on the slate and that the cleaner has partially damaged/removed the coating – so the streaks could be ‘clean’ spots – or where the alkaline or solvent in the cleaner has partially dissolved the coating and then left a concentration of the now damaged coating in streaks

    Or it could be a deposit (soap, oily, waxy etc) from the detergent itself.

    Try some hot water with w neutral cleaner (like a few drops of washing up liquid) and rinse well afterwards

    Also you could try some solvent – a good one is acetone and the easiest way to try this is just take some clear old fashioned nail varnish remover, dab a bit on onto the streaks, and rub. let it dry and see if it has A) removed the streaks and nothing else, B) removed the streaks and something else – maybe coating, made the slate look dull, or C) – does nothing

    Try this and come back to me

    Hope this helps


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