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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. Thanks ian i will have a go as advised.

  2. I recently removed small rugs from my slate floor and noticed that the non-skid pad under the rug is stick to the floor. I fear that even though I waited a couple of days to put rugs down after sealing it (about eight years ago) I may have put it down too soon. I have removed most of it with a light scrubber. But there is still something there that I can actually scrape off with my fingernail. Obviously I can’t do that to two 5×7 foot spaces. Any ideas on a product that might help? Thank you. It’s is a great website! Very helpful.

  3. I have black slate on the hearth of my fireplace. My toddler left a sippy cup of milk on its side on the slate. There is now a white stain on the slate. It turns back to original color when I wipe it with a wet cloth but the stain comes back when it dries. Any suggestions on getting it out?

  4. Hi
    I have read through these post an I don’t think this question has been asked, but apologise if I am doubling up. We have recently moved into a house with slate floors (dark brown with an uneven textured finish). The previous owners had a rug down along the breakfast bar the prevent scratching the floor with the bar stools, however I don’t think it has even been lifted up to vacuum or mop under and now the rug is well and truly stuck to the floor with what i assume to be the build up of grime, spilt drinks etc that has probably occurred over the years. Any suggestions on removing the rug easily without damaging the floor or putting my back out from trying to rip it up?

    Thank you in advance for any suggestions.

  5. Hi Samantha,

    I think you are going to have to carefully start to roll back the rug, and have a new, sharp, wide bladed scraper to hand to try to free the backing, it will be a bit like shearing sheep if you can imagine what I mean, and will inevitably leave bits of the backing on the floor and the occasional metal mark form the scraper (you may be able to find a hard plastic scraper which might be better)

    once the rug is up, I would suggest a mixture of a high alkaline cleaner and an abrasive cream cleaner to deep clean the floor and remove the traces of backing – then rinse the floor and assess it’s sealing requirements

    Hope this helps


  6. I would try an alkaline cleaner, and maybe a cream cleaner with a small amount of abrasive it=n it first – if it is a residue of calcium from the milk, something mildly acidic might help.

    Milk contains both lactic acid, and calcium, as well as oils and fats so it is hard to know for sure exactly what is causing the issue, hence a little bit of experimentation – a cream cleaner is very mild and you are relying on the abrasives within to gently rub off the stain. In the USA you can get a product called Nanoscrub.

    Hope this helps


  7. Hi Lisa,

    You could try a micro Abrasive cleaner like nanoscrub or similar. Failing that you may need a solvent sealer stripper, this will obviously affect the sealer so will need to re seal after

    Hope this helps


  8. Thanks Ian for the advice and quick response, we will try that, hopefully we can get it up without to much damage to the floor.

  9. Hi Ian

    Started reading through your posts and then realised how many there were so thought I would email directly, as you seem to be very good at responding and certainly know your stuff.

    We live in Wales and have an old, derelict cottage on our land. We have used some of the floor slates from this cottage to lay a floor in our kitchen. The slates are big – most of them at least two foot long by at least 14″ wide. They are nearly all at least 2″ thick. The cottage, and therefore we presume the slates, is about 150 yrs old.

    They have been laid on lime, with tight gaps between them which have been grouted. The slates were just brushed down before we laid them – so they were anything but pristine to start with. As we have been working on the kitchen (for what is probably a good year) they have collected plenty of general dirt, dust and the odd splatter of plaster, the big chunks of which we have managed to get off. They are currently a dusty unpleasant grey/brown colour. They are quite uneven in their general appearance – lots of dips and undulations.

    THe building work as all but finished now and we are at the point where we want to clean the floor up properly and maintain and care for it correctly. Obviously when I wipe the floor with a wet cloth, the blackness of the slate comes up lovely, and then disappears. I really have no idea what to do to get this really clean, seal and protect it and care for it in the longterm.

    Please could you help with suggestions and names of products etc? We would like to keep things as natural as possible, but realise that, at least during the initial clean up, we might have to use something stronger.

    Many thanks

  10. Hi Natasha,

    OK, well you have very old, riven slate slabs, and they are probably fantastic.

    Fixing them on lime may create issues – Do you mean a lime mortar? I am guessing this was because for some reason, in the old building, a proper concrete floor was not possible?

    There are a couple of points, one is that if you have no concrete, you are also not likely to have a properly installed damp proof membrane (I am making assumptions here). This in itself may not be an issue, as for years, in traditional housing like this, it was the highly moisture-resistant nature of the Welsh Slate that led to it being used as flooring (and of course for its durability, aesthetic qualities, and its plentiful supply) It was the slate itself that created the damp-proof layer.

    So I do not see you having too many issues with damp etc, however, the tight joints and will have been hard to grout fully, there will also be inherent movement on the lime mortar so there will be fine cracks between the slates. This means that when you wash the floor – water can get down into the lime mortar – if this happens, then when the floor dries out after cleaning, it could kick start some efflorescence – growth of white crystalline deposits, coming up through the grout joints.

    If you feel the joints are well sealed with grout then you may be ok.

    After building work like this it is typical to use a mild acidic cleaner, one based on a mild acid like phosphoric as much of the dirt will be mineral based (cement, plaster, building dirt etc) and this type of cleaner should not harm the slate – but do a test first of course!) Do NOT use a brick acid, or one based on HCL. Once this has been done, and the floor rinsed and dried, you may now see other things on the slates such as old layers of polish and general, ingrained dirt and grime. At this point you could switch to an alkaline deep cleaner, and use it with a micro abrasive cleaner like Microscrub.

    Just make sure you manage the water and get it picked up – do not leave it to linger too long.

    For the acid wash:

    1. Pre dampen the surface with a wrung out mop
    2. apply diluted acid cleaner (see bottle) with mop to a workable area – say a couple of square metres at a time. Leave it on for about 2 minutes
    3. now scrub – preferably with a rotary scrubbing machine with a medium hard nylon brush head – if doing by hand then it is best with an old fashioned nylon scrubbing brush (deck brush)
    4. Pick up the dirty solution with a wet vac if you can – other wise it is a lot of mopping, chancing water and rinsing – you can hire a reasonable wet vac at any tool hire store – it will save you hours of work.
    5. Rinse out your mop, put fresh water in the bucket and mop the floor again – this is to rinse the floor
    6. Wet vac again
    7. Rub the floor dry with an old towel.
    8. Do not skip any of the above points!

    when dry, you may have to do this again, the downside of using a mild, safer acid is that it works on thin films then is spent, but this is the safe way to work, taking little bits at a time. limit the time you expose the floor to water by picking it up and drying it as mentioned above. If you need to do an alkaline clean after, then you will need to use more water, for longer, but that is not really avoidable.

    Let it dry out for at least a coupe of days, preferably a week (give time for any moisture to out of the the lime mortar bed.

    See if you have any whitening at the joints – if so, a quick wipe with some more dilute acid cleaner, rinse and rub dry immediately may sort this – then wait again, until you are happy you don’t have a re-occurring efflorescence issue).

    Sealing is another question, after cleaning your slate may have a rather subdued and dull or lifeless appearance. If you like the deep black of the slate when it is wet then you have two choices, a coating sealer (that will last a limited time say, 6 months to 3 years) or a colour enhancing sealer that will last a lot longer.

    There are issues with both, topical is easy to apply, looks shiny, or at least has a low sheen, so looks clean and also helps cleaning as the surface will be easier to wipe down. However if you don’t like the sheen, (some feel it looks artificial) then you may not want this, also it is on top of the slate, not within it so it will wear and be subject to attack from your cleaners.

    The enhancing sealer (such as All for Stone Enhance n Seal) will bring out the colour, without the shine, but the floor must be bone dry, including making sure there is no latent moisture in the lime mortar. Also this would be a permanent solution, there is not taking it back out if you don’t like it.

    Hope this has helped


  11. I have a black slate floor in my kitchen…recently i cleaned it with Cif floor cleaner and it has left a white bloom residue on some of the slates…the rougher ones.
    Please have you have a method of cleaning i can use to remove it !

  12. Hi Ian

    Thanks for such an informative reply and apologies for the delay in replying. You are correct that in that we used lime mortar – there is concrete and a damproof course underneath though. WE used lime in case we ever wanted to get the slates up again – it would cause less damage to the slate than using concrete. And you’re right too about them being fantastic!!

    We don’t have any damp problems and the gaps, although quite narrow are well grouted.

    Will follow your instructions – I;m sure they will come up lovely!
    THank you again for going into so much detail – I really had no idea where to start with all this.

    Best wishes

  13. Hi Anne,

    OK, it could just be a residue of the cleaner – try wetting the floor and adding a tiny bit more CIF – to ‘clean it self’ by re-wetting it, with more of itself, you may find you can break it down and wipe away – if you can, immediately after (before it dries again) rinse with clean water and a clean cloth.

    If this does not work, then maybe you have partially removed what was left of a coating sealer – Imagine having finely painted nails (no, I don’t know what this is like, but I have daughters!) and you inadvertently rub one of them with an emery board – it takes some of the coating, (the varnish) off, and maybe the varnish starts to look a bit ragged, and even white at the edges, so the only option now is to completely remove the rest of the varnish (from that nail at least) and start again.

    As Cif is an abrasive, it may be just enough to damage, or scuff the coating sealer on the slate, but not enough to fully remove it – so consequently you can now see damaged sealer made opaque by the Cif, that you were not aware was even there – in which case, you may have to get a sealer stripper to remove it, then re seal

    Hopefully it is the first one

    best of luck


  14. Your welcome Natasha

  15. Hello Ian, Apologies if this query has already been asked/answered; your advice would be very welcome. I have Chinese black slate tiles on my kitchen floor which I laid over 10 years ago and sealed with Lithofin Slate Seal. In preparation for reapplying this product to reproduce the lovely shine the floor had originally, I’ve steam cleaned the tiles using my wallpaper stripper “pad”, after spraying the tiles lightly with a degreaser, scrubbing with a nylon abrasive pad, rinsing with clean cold water and allowing to dry naturally. There are places where a white bloom or efflorescence has appeared, some of which seem to reflect the shape of the wallpaper pad (straight/rectangular shape). Am I able to remove these marks and if so, with what? I suspect that if I reapply the sealant without removing the white marks they will still show up. Thank you in anticipation of your response.

  16. Hi,
    Our slate shower has developed a whiteish/grey speckle over the tile. We seal it yearly but we believe water has gotten in behind the seal (maybe through the grout – who knows).

    How can I fix this problem? Do I need to remove the seal, scrub and reapply. The local tile shop suggested I usse sugar soap but that sounds a bit wrong to me.

    Thanks for any help you can offer

  17. Hi Sue,

    I suspect it is not an efflorescence bloom (especially on slate, it would most likely show up first in the joints). The steam pad shaped mark is the clue – I think what you have done is partially stripped what was left of the slate seal – breaking it down where yo have let the pad linger, and so destroying its structure and integrity – making it opaque in the process.

    So I would try a stripper on those marks (to see if you can complete the stripping that the steam cleaner started). One little tip you can try is to dab some nail varnish remover (the old acetone type) with a cotton wool pad and see if that removes any thing. If it does then great, it is telling you that a solvent type sealer stripper would do the job.

    If so then you will need to consider stripping the floor completely, before reapplying any sealer.

    Hope this helps


  18. Hi Sugar soap is basically an alkaline cleaner – it may do little here (wont do much harm either apart form degrading your sealer – but you may have to remove that anyway).

    It sounds more like hard water deposits/soap-scum etc to me – if so it might be a deposit on top of the sealer. I would try something very mildly acidic first – a proprietary cleaner based on citric, sulfamic or phosphoric acid (or similar) – nothing strong though – so no Muriatic (HCL).

    you may find that it just come s right off with a mild acid wash.

    Hope this helps


  19. Thanks for the advice Ian. I’ll try the acetone route first. As it happens, I have a quantity of acetone from ex-nail salon use in my garage! Can you recommend a solvent type sealer stripper should I need this? Thank you again. Sue

  20. Hi Ian,

    Really great blog.

    I have a different query about a slate fire surround. I live in an 1880 built flat in Edinburgh and my fire surround is made up of what appear to be matt black stone. It has very flat and smooth finish but there are a couple of areas of the black missing, exposing a slate textured grey surface, so it seems like it is coated with something. I guess the coating was for decorative (maybe make it appear like marble or something?) and protective purposes. The black colour is quite dominant in the room and ideally I’d remove the coating to expose the natural stone below, to soften the appearance. I’ve tried acetone and nitromers paint stripper without any success. I’ve tried scraping a little and the stuff does come off but it is quite adherent and doesn’t chip off, more scrapes off. I don’t want to scrape it all for fear of damaging the base stone.

    Have you come across this before? Is it a particular coating? Any suggestions in how to remove it? Reading through your blog for tips, it seems like an abrasive grind/polish might be needed?

    Any suggestions would be appreciated.



  21. Hi Sue there are various ones out there but yo can try a paint stripper white spirits or a proprietary sealer stripper

    hope this helps


  22. Hi Blair,

    It could be anything, people have put all sorts on slate over the years, oils, linseed, poly-urethane coatings, varnishes etc.

    You have tried the obvious things.

    You know, without seeing it, it is not easy to advise but it could be that there is no actual coating, just that the surface has been mechanically polished – this would make the naturally riven slate surface, flat and smooth and allow the darker colour to come through. The patches of the lighter colour could be where that polished surface has been damaged/chipped etc.

    Either way you may have to resort to removing the ‘polish’ by mechanical means –

    You will not get back to a natural ‘riven’ finish as that is the finish that occurs when slate is split (by a skilled craftsperson) along its natural cleavage plane. But you could use coarse grits or honing powders to take the polish back to unpolished or a honed finish (honed is flat and smooth, but not necessarily reflective, so not like polish, the dark colour will be less intense) .

    This is not always easy to do in situ and if you can take the surround down and take it to a stone professional , it would be easier to do on a bench. If that is not possible then hand held polishing machines would be needed with a pad head that can apply honing powders, A honing powder of grit 500 or 400 or below should remove the ‘high polish’ (the small the number number, the coarser the grit – so 400 grit is not as fine as 500 etc)

    Hope this helps


  23. Hi Ian,

    My grandmother has a stain on her slate tile floor that was created from a cow hide rug. It is whitish and spotty. Do you know how we could remove this?


  24. Hi Ashley,

    I am not sure if it is something that has been deposited by the cow hide (some fats, tanins or other material leaching out from it?) or if it is just that the hide, in covering the floor, blocked the stone’s natural tendency to ‘breathe’ If there is any moisture beneath the stone that has been trapped by the hide then it could be efflorescence – soluble salts being left there.

    Or it could be that it is some kind of mildew/mould etc.

    Try just wiping over some of the white spots, with a damp cloth. If they disappear immediately, but come back as soon as the floor is dry, then this might indicate efflorescence, if so a mild (and suitable) acid based cleaner, used very dilute may be all that is required – so you could try this, but make sure that A) – your slate is not acid sensitive (most are ok, but some of the more colourful ones can dull a little bit) and B) that you do not use a brick acid, based on HCL –

    failing that, try a good high quality alkaline deep cleaner and a scrubbing brush.

    If this does not work, try a solvent stripper type product

    Let me know how you get on

    Hope this helps


  25. Hi Ian,
    Wondered if you could help- we have a slate hearth (not sealed) and someone has cleaned the ash with a baby wet wipe which contains some bleach. This has left white marks along the edges of the tiles- can I restore them to their original colour/ will they be permanently glossy if I do so?
    Many thanks,

  26. Hi Chris,

    First of all, baby wet wipes that contain bleach? – Not sure I would want to wipe my baby with such a product??

    OK, you say the slate has not been sealed, but perhaps it has had some treatment (slate oil, some kind of polish, particularly one that contains some kind of colour that will darken the slate a little)?

    I am not convinced that this is a bleaching issue but lets look at what bleach might do and what it should not do: First of all, I doubt very much if even household bleach from a bottle, would really damage a good slate, if the slate is dark grey or black, or green it ought to be a pretty tough material, very old geologically and NOT usually containing any colours or pigments that are mobile, or able to be bleached out.

    However if there had been some kind of treatment, like a colour enhancing slate oil or similar, then the bleach may well have had some effect on that, given what I would hope to be very small concentrations of bleach in the wipes, the effect would be minimal. If this were the case then you may need to clean the slate again, to remove all of the treatment, (so use an alkaline cleaner or solvent stripper) then re treat afterwards.

    My gut feeling is that it is more likely to be a residual deposit from the wet wipes: Whether they contain bleach or not, they will contain lots of things, and unless you rinsed the slate with fresh water after using them, the wipes may well have left some solids or residues. As the slate is likely to be fairly impervious, the moisture will naturally collect at the edges, and at the grout joints which will retain moisture for longer as they are more porous – this seems consistent wit you saying the white marks are at the edges.

    I am sorry I cannot be more precise, do you have any photos you could send me? It might help.

    Things you could try:

    You could try using a high alkaline cleaner and a scrubbing brush, or scrub pad – rinse after and buff dry

    Use some acetone (clear nail varnish remover) – just rub a little on some slate witha cotton pad and see if you get any colour transferring – this will indicate that there is something in the slate (oil or otherwise)

    If you know without any doubt that the slate is untreated in any way, then I really think we are dealing with a dried on residue from the wipes, which means it ought to be removable, it is just case of trial and error to find the most appropriate method/product.

    One other thing that may be worth a try is to use a micro-abrasive cleaner like Microscrub, mildly alkaline and using abrasives derived from calcite, it is soft enough to not damage the stone, but it may help shift stubborn stains

    hope this helps


  27. Any suggestions, please.The stove installers sprayed our untreated, light grey slate hearth (made from an old billiard table) with WD-40. They said it would dry back to grey when we protested. It hasn’t and looks like a lump of black ceramic tile which is not what we want. Can anything be done to remove the WD-40?

  28. Hi Bill,

    OK, I have not tried to remove WD – 40 but it is an oil. If it was just one spot or two then a poultice may be useful but as it is all over you are going to need to use some kind of liquid. First thing I would try is a high alkaline cleaner such as Xtreme Clean by All for Stone.

    If this does not do it then you will have to use a stripper (solvent) the slate from snooker/pool tables is often Welsh as it can me made with a very flat surface. If yous is this material, then it is very dense, and with a bit of luck the oil will not have penetrated too deep.

    One quick test you can do, is this: if you can get your hands on some clear, old-fashioned nail varnish remover (the type that contains acetone) – try dabbing a little onto a cotton pad and rubbing a small test spot. If it comes off and leaves the slate, back to its natural light grey colour (and also removes any trace of artificial shine) then this is showing you the oil is removable, I would not suggest doing the whole thing with nail varnish remover, but it does act as a good tester.

    If it comes off easy with the nail varnish remover, then you could try a paint thinner/stripper from a hardware store, but you might still try an alkaline cleaner first – the reason is some solvents, due their oily nature, can in some cases also leave a slightly darkened finish

    Hope this helps


  29. I have a metal plant container on my outside brazilian slate terrace and it has been leaching rust for the last two years. I did seal the slate when it was laid with lithofin, but haven’t resealed for about two years.
    I have been hunting around the web for a solution, but yesterday decided to try my favourite product Astonish mult-use cleaning paste, which is gentle enough to use on enamel. I used one of those sponges with an abrasive side on it. Guess what! It came off!
    I hope it works for you.

  30. Thanks for sharing that Jano, yes that product can sometimes work, along with the nylon scrubbing sponge. Provided the rust is just a deposit on top of the stone and it has not had a chance to get too deep into the surface. Like Microscrub, your product contains fine abrasives that can get into the texture of the stone without damaging it.



  31. Hi Ian,

    Great site and I hope you can help. I have black floor tiles in my kitchen and think they are slate, I am not sure is they have been treated in anyway but believed that they are. My wife tried to get rid of some staines by using Flash bleach and left the cleaning product to soak into the stain. As you guess this has now left large spots of white staines on the black flooring where she has sprayed and left the bleach. Please could you help and tell us how we could restore the tiles and remove the bleach stain.

    Many thanks


  32. Hi Raj,

    This could be a number of things, first of all, if your slate had been treated, especially with a kind of coating sealer (this may have left a slight sheen) then the bleach will have partially broken this down, so, in this case, the white marks are the remains of damaged sealer. The only answer here is to break down and remove the rest of the sealer. If you can find out what sealer was used, and get some more, you may be able to get away with just removing it from the tiles where the damage has occurred, (but make sure to strip the whole tile, edge to edge), then when rinsed and dry, just re apply the sealer to these tiles. If not you may have to strip the whole floor.

    You could try adding some of the bleach to water, and leaving on a whole tile (where there is already a stain) for a few minutes) then scrubbing all over the the tile with a nylon sponge scrubber or scrubbing brush, rinse and let dry- this may help you blend out the stain.

    Failing that use a reputable sealer stripper.

    It could also be residue of the bleach, a good clean with an alkaline cleaner, or a little more dilute bleach, and a scrubbing brush may resolve this, just do not leave it to soak and also dry in, leave it just a few minutes, keep it wet, then scrub, remove, rinse with fresh water then dry.

    I have seen, in a few rare circumstances, some slates that are let’s say a bit cheaper, or supplied from less trustworty sources, which have been artificially darkened or coloured. IF this were the case the the bleach may have removed some of the artificial colouring to reveal a much lighter ‘real’ colour. However I am guessing that a part stripped sealer or residue is more likely

    Hope this helps


  33. A slate floor was put down in my bathroom but the wrong sealer was used. I wanted an enhancer put down but an impregnator was put down instead. Miracle 511. I’m assuming the Miracle sealer and enhancer I originally wanted to use will no longer work. Any suggestions as to how to get the impregnator sealer off? Some say vinegar, others say no.

  34. Hi Elaine, you will need a sealer stripper, you could contact Miracle’s tech services department and ask their advice. Some of the enhancing sealers on the market cannot be guaranteed to work 100% even after stripping, as it is not always possible to remove 100% of the original sealer, to the point where the enhancing sealer can get in and work

    Hope this helps


  35. Hello,I have reclaimed about 25sq mtrs of delabole
    Slate from a site.Want to use it for my c16th cent
    Cottage floor.The slate came originaly from an c18th house.
    It is currently covered in moss and brown dirt.Tried scrubbing
    With jays fluid and stiff brush,it does gradually remove the dirt,
    However it would take me about 6 months to clean.Any ideas (these are large meter sq slates.

    P.s great site.


  36. Hi Kevin,

    OK, the Jays fluid is good at killing algae etc but you may need something a little stronger as a cleaner (but not a disinfectant) to do deep cleaning. Or you may need to do a combination clean.

    I have had success with similar things in the past using a high alkaline cleaner like Xtreme Clean in combination with Microscrub.

    Pre wet the slabs, then apply some of the alkaline cleaner (diluted) leave it to dwell for a good 10 minutes
    then add a small amount of microscrub, and scrub using a scrubbing brush.

    It might take several attempts.
    Rinse well after each wash, you can also then try using a little watered down house hold bleach just to finally kill any remaining green.

    Rinse thoroughly, maybe with a little soapy water

    Good luck

  37. Hi Ian

    I have a smooth, black, Welsh slate countertop, which was perfect at installation, and now is speckled due to lime and lemon juice spills. My slate supplier said to use steel wool to remove the Lithofin sealer and then re-seal. I’ve tried this but the outline of stains does not diminish. Any clues please? A webpage suggested baking soda and lemonjuice applied overnight … Help! Thanks for any advice …


  38. Hi Ruth,

    OK, well Welsh slate is so dense that not a great deal of sealer actually penetrates the surface. So what sealer is there tends to coat the surface and is therefore prone to easier removal – by use, including abrasion and from exposure to chemicals. Some sealers are better than others are resisting acidic chemicals (like lemon and lime juice). I don’t know exactly how that one will have done

    It is possible that there is a slight stain from the juice (that has got past the sealer) or, it could be that the acid contained in the juice has simply damaged the sealer and partially removed it. If this is the case then all is not lost, but attempting to clean it is not going to achieve any thing. You may need to remove some of the sealer – (what you are thinking of as a speckle stain, might actually be the actual slate, where sealer has been removed). In any event try a small test on one of the affected areas using some acetone (if you have some clear nail varnish remover this will do) rub a little NVR on a cotton pad and rub over the affected area – if it makes the speckle apparently bigger then it is removing sealer from the surface – making what you see as the problem ‘bigger’ but in reality is just cleaning the sealer off the slate. let it dry and see if you are now back to a clean slate surface. If so then you can try to re seal that area. If it is possible to reseal in just those spots affected (without it looking patchy or inconsistent against the older seal) then go ahead. If not then you would have to consider stripping the entire surface (or at least a whole section). It might be a pain to do the whole slate with NVR, so you could try to get a proprietary sealer remover

    Hope this helps


  39. Hi Ian
    I’ve just had a green/grey slate floor fitted.

    I’ve noticed that some of the tiles have white marks on them. These appear to be along the contours of some of the tiles. It’s not on all of them though.

    Would this be efflorusence?

    The tiles have been recently sealed, what can do to remove the marks?

    Thanks very much for your help.


  40. Hi Dan,

    It could be efflorescence, slate being very dense, any moisture that may be trapped in the structure is likely to escape via the joints, and so that could account for a mineral deposits along the edges and corners. IT could also be small bits of over application of the sealer (if the sealer was left to pool in the joints, as it runs off the slate etc) then you can get small shiny/white spots where too much sealer was left on.

    A quick test: wipe the marks with a damp cloth, if they seem to disappear or at least become translucent, but come back when dry) then this is consistent with efflorescence and a very mild acidic cleaner ought to help – use a safe acid based on phosphoric acid or sulfamic acid, and dilute it well, pre-dampen the floor first with water and rinse well after. Try not to let the floor stay wet for long, do a little bit at a time, and dry it with a towel, this way you reduce the likleyhood of creating additional efflorescence through the added moisture.

    If the test does not make the spots disappear, then it might be that you have sealer residue spots instead -and they would need to be removed with the sealer stripper, or you could try some clear nail varnish remover on some cotton pads.

    Hope this helps


  41. I have white stains on my flagstone that won’t come out even when I use diluted phosphoric acid.

    The problem started when I used Quikrete PowerLoc Jointing Sand to fill the joints.

    I can send a picture if you give me an email to respond to.

  42. Hi Bob, apologies, I missed this one. Yes send ma an email ( use the contact us page on the site)



  43. Ian,

    I emailed the pictures to you last week. Did you get them?

  44. Hi Bob, Sorry, no I have not received them



  45. I sent the pictures to the donotreply email address which obviously doesn’t work. What email do I attach and send the pictures to?

  46. No Worries, there is a contact us form on the site most people manage to contact me that way, once you send me a quick message I can reply and you will have my email address



  47. Hi Ian firstly great blog

    I have a slate floor I didn’t like the original grout so I removed it using a buzz tool, unfortunately when removing it the tool would sometimes jump out the grout lines onto the slate leaving a lovely scratch. So I have now replaced the grout and buffed out the scratches, however where I have buffed out the scratches the colour is lighter than the rest of the tile. Can you provide any advice on how to get the same colour back? I have sealed it several times and have also sealed the affected areas only several times and the buffed areas are still pretty noticeable.


  48. Hi Richard,

    OK, first of all is your slate dark? – like dark grey or black? Often scratches in this type of stone look white or very light grey by comparison.

    What I don’t know is if there was originally any kind of stain (dye, oil, unlikely) applied to the slate which imparted an artificial colour, or, an enhancing sealer – (perhaps more likely). If so then scratching through the surface also removed whatever had been applied.

    IF this is the case then you would need to know what it was and apply a little more BUT, that may not be possible now that you have sealed it several times.

    However I think it more likely that the scratches are much lighter just because the finish of the slate may be smoother than the surface left by the scratch. The rougher the surface, the dully/lighter the colour.

    It is my guess that the buffing you have done, has blended the scratches and made then smoother than they were (reducing their intensity) BUT, has not reached the same level of fineness as the rest of the slate. What did you use to buff? – a cloth would not do much, and sandpaper would leave the surface too rough. You might try the finest wet and dry emery paper.

    Have you got an photos you could send me so see if it helps further?

    Hope this helps


  49. Hi Ian,

    My husband brought home an old schoolhouse chalk board slate piece this past weekend that had a few paint marks and other etched areas, so I looked up how to remove paint marks, and an internet source mentioned acetone, so I pulled out the generic “acetone” that I use for removing nail polish and it seemed to work on some of the varied colored paint stains around the border area (where there was most likely a wooden frame) so after testin it, I went at it. However, there was another area that I assumed was green paint somewhat in the middle of the slate, so I put the acetone on that and rubbed aggressively, and it seemed to make the spot even bigger and greener! Ahhh! Now I fear that I ruined my salvaged piece. I cleaned the entire slate with soap and water and then followed up by drying it with a paper towel, but the (now bigger) green mark is still there. When I wipe the slate, dark discoloration does seem to appear on the paper towels, by the way, which seemed strange to me because I don’t remember that happening when I cleaned classroom chalkboards with water for my teacher as a child. Please advise about what I should do to possibly fix my bigger, green, revealed smudge/discoloration. I am so sad 🙁

  50. Hi Heather,

    Hmm, interesting one. Sometimes these problems can be the opposite of what we think we are seeing. Can you tell me, is the back of the slate also black? I think there may be a slight clue in your own word: “revealed”

    I am thinking that instead of spreading a discoloration, the black colour (which comes off on the cleaning towels) is actually the discoloration – or, if you like the ‘intended, deliberate ‘coloration’. What I am getting at is that perhaps it is in fact a GREEN slate, that has been died, stained or painted black for use as a chalk-board. And so your use of acetone has broken down the ‘paint’ and now that is more easily removed, ‘revealing the natural slate colour beneath – only one way to test this though; try some more acetone in an inconspicuous area, maybe on the back? See if it takes black colour off to reveal a green slate.

    In your part of the world there are some very good quality slates (very dense, hard-wearing, able to be fine-honed to give the smooth writing surface required) but they may have been more green in colour, and so were painted to make chalk boards.

    Do a quick Google search for “Vermont green slate” – see if the images you find look like the green you can now see

    If this is the case, then there is nothing you can do, as restoring the slate means either stripping all the paint off it to reveal its natural (and rather beautiful) green colour, or, painting it an artificial black again.

    If my guess is wrong, then I am not sure, it is odd that the black colour comes off. Some dark grey/black slates do have green patches in them; this is natural and to do with the mineral content being unevenly distributed in the stone – this image I found shows the very common green spots found in Welsh Slate (source:

    It is possible that your slate is dark grey/black but had some natural green patches which the previous owner masked with come kind of paint or stain – I could not advise on what would be a suitable product to re instate this as it is gpoing to be an nunatural coating of somekind (paint, dye etc)

    What happens to the green patch, when you simply wet it? does it go dark and black or is it still clearly visible as a green albeit now wet, patch? If it disappears then many stripping the slate and sealing it with an enhancing sealer could be the way to go

    Hope this helps


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