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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. 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.


  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?


  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


  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


  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?

  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


  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


  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?

  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?


  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?

  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


  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


  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


  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


  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

  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

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