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Cleaning Slate – Expert Advice on Cleaning Slate and Slate Floors – Part 2 »

Some detailed instructions with regard to cleaning slate floors:

If the slate floor is adversely covered in cement or grout residue:

1. Use water to pre-wet the floor.

2. Apply some phosphoric acid-type cleaner solution to the floor – mixed with 1 part cleaner to 5 parts water to begin. (You can use a stronger mix if required). **PLEASE NOTE: Always conduct a small test on a relatively inconspicuous section of the floor first, before you begin.

3. Leave the cleaner to dwell on the floor for a few minutes

4. Agitate the floor and cleaning solution with a scrubbing brush (nylon bristle and not metal).

5. Soak up the cleaning solution remaining on the floor. Rinse well with fresh water, agitating again so you can get rid of any residual acid cleaner.

6. Make an assessment of the floor at this stage. You may need to apply an additional treatment of the cleaner.

If your slate floor only requires routine cleaning we would recommend a neutral cleaner like Ezy Clean by All for Stone – this is a mild cleaner and is safe and suitable for cleaning slate on a regular basis.

For more intensive slate cleaning, where the dirt is not mineral- based, we would recommend the use of a heavy-duty alkaline cleaner like Xtreme Clean. This a powerful cleaner and degreasing solution. When applied to the floor, leave to dwell for between 5 and 15 minutes, depending on how bad the contamination. Then agitate by scrubbing with a nylon or natural bristle scrubbing brush. Clean up remaining the dirty solution and rinse well with clean water.

The critical elements here are the dwell time and the rinsing. Alkaline-cleaning solutions need time to work. Once you have “extracted” the dirt from the floor it will be suspended in the solution so you absolutely must remove it – on no account leave it to dry naturally.

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


  1. Ian

    I just bought a home in the mtns of CO and the showers have slate in them. There seems to be an iron like substance in a couple of them on the floor. First, what exactly is it, second, how is it caused, third, how do I get rid of it, and fourth, can I prevent it. Hoping you can help.


  2. HI Diane,

    OK, when you say Iron-like, do you mean rusty looking?

    Many slates have, as a naturally occurring mineral, some form of iron in their makeup. It is completely random and perfectly natural, not a ‘fault’.

    If however there is some surface rust, that is, some rusty deposit that has landed on the slate, usually from some rusty item above it, either in the current situation (rusty faucet, fitting etc) or something that the slate was in close proximity to during storage (strapping band with steel fasteners for example) then this is not an inherent part of the stone, but rather a deposit that has been left on the surface. This can often be removed with a mild, phosphoric acid based cleaner.

    Sometimes, where there is naturally a occurring iron-bearing mineral, it only starts to oxidise (rust when the slate is split, and installed, (thus exposing the iron to moisture and air) – so it rusts at the surface, sometimes a phosphoric acid based cleaner can help remove or at least reduce, this also.

    There is no real way of stopping it reoccur if it is natural iron, sealing it may help (reduce the ongoing contact with moisture), but it may settle down over time in any case.

    Hope this helps


  3. My son has a slate floor in his kitchen and lounge. In the kitchen there was a larg cupboard now removed for the new fitments This had beeen there since building in 1960. It is dark gray but a much lighter “dusty” colour;

    How o I clean it up? Hyrogen hydroxide has not made any difference

  4. Hi Valerie,

    Hydrogen Hydroxide? – do you mean water?

    Anyway, for old slate like this my first test would be with an alkaline deep cleaner, like Xtreme Clean. maybe with the addition of a micro abrasive cleaner like Microscrub.

    It all depends on what you are trying to remove, the above works well on general ingrained grime but if the slate had been previously treated with some kind of sealer, oil or coating then you may need something stronger

    Kind regards


  5. I have a friend who was doing a spray paint project on her slate patio and, even though she put some cardboard and plastic down, she has overspray on whatever wasn’t covered. What can she do to remove it?

  6. Hi really she needs a paint stripper.

    You can saturate the slate esp the area surrounding the stain with warm water, wipe the water away from the paint area – this can just sometimes help to prevent the solvent based paint stripper from pushing the thinned paint deeper into the stone.

    Apply a stripper, leave for a few seconds, rub, and immediately wipe up any dissolved paint with absorbent paper towels etc. repeat if needed, each time removing more of the paint. Do not let the solvent / paint dry, always remove what you have dissolved before it dries.

    Hope this Helps


  7. Hi there we have slate window ledges but they have been painted’ we would like to restore them to their former, glory how would you recommend we do this?

  8. Hi, you are going to need a paint stripper I think, a chemical one. You could try a heat gun first, if you can get the paint to peel off with one of those you may get a way with a nice clean stone. If not look for a paint stripper, to suit whatever type of paint it is, then conduct a small test on one corner. As soon as the paint softens try t remove with a plastic scraper or similar so as not to scratch or gouge the stone. Then wipe away excess stripper and rinse with a nylon scourer/sponge and fresh water. Let it dry and evaluate the degree of success – it may work first time or may require a second go.

    Hope that helps

  9. Catriona Lynch

    April 30, 2016 at 7:36 pm

    I used a softish kitchen scorer on a section on our slate fireplace. The area has gone all dark, Matt and generally dirty looking . Is there any way to repair the damage? Thank you in anticipation

  10. Hi,

    I am not entirely sure what has happened here, it could be that you have inadvertently removed some coating / oil/ wax or other finish, or you have partially polished the surface – to a very small degree, or a bit of both. Any chance you can send me a picture?



  11. Hi, I have split slate tiles on the wall. We made a mistake and put on ‘colour intensifier’ and it is turned black instead of the grey tones. We want to take it off and get back to the grey. Do you have any ideas how we can do this please?

  12. Hi, All I can suggest is a very strong alkaline cleaner or perhaps a solvent stripper – but the first thing I would do is to call the manufacturer of the colour intensifier to ask what their recommendation is.

    It might be that you cannot remove 100% of it, but you may be able to reduce the intensity to an acceptable level>

    Hope this helps


  13. Hi, we have a beautiful Lakelans cottage which is 120 years old and has original slate flagstones in kitchen and lounge. We recently needed our kitchen rep mastered prior to have the kitchen updated and the plaster dust is proving hard to get rid of. I have used washing up liquid and a nylon scrubbing twice. Then used bleach and elbow grease. It has improved but not gone. The floors are not sealed. Would an acid- based cleaner be best? Hope you can help.

  14. Hi, a very quick answer, yes I think that a very diluted cleaner based on Phosphoric Acid will help, as the plaster is a mineral product and needs something to actually dissolve it. Look for something like my Grout Haze Plus on amazon or other products that are similar such as HG Extra

    you will need to a) dilute at least 1:5 with water, b) rinse well with water afterwards and c) do a test area first

    Hope this helps


  15. Hi,
    I have a new hearth pad for my wood stove that is made of cleft silver slate. The surface is beautifully rough, textured and sparkly. The problem is that the mfg flooded the surface with sealer but did not work it into fine crevices or mop it out of the low spots. In the crevices and whorls small bubbles were trapped underneath the sealer making it look like snot and the thick layer of sealer in the low spots is milky, obscuring the beauty of the stone. The entire hearth needs refinished but because of the rough texture I do not know what product to use. Many of the strippers form ‘goo’ when they react with the sealer and I am afraid I could not get this out of the rough, textured stone.
    Any suggestions on how to proceed will be appreciated.

  16. Hi,

    OK, you have a thick coating, too thick hence the pooling that has resulted in the collection of ‘pools’ of sealer in the crevices etc. which have then dried trapping air bubbles and also drying white (this can be due to moisture or forming a skin and not fully setting beneath the skin) – either way just too much has been applied. You are going to have to remove it with a stripper.

    Yes the stripper will turn it to goo – that has to happen, it is the stripper breaking down the sealer and re-emulsifying it it. The sealer will soften, re-emulsify the sealer and this will turn it into a sticky mess, depending on the stripper, this will take differing amount of time but usually a slower acting one is best, it will take longer to soften the sealer, but also it will not flash off as fast, leaving a dried and damaged/altered residue.

    The normal procedure is to apply the stripper and leave it ti sit/dwell – as recommended by the product instructions. this could be from 10 to 15 minutes , to upwards of 45 to an hour. Whatever the time, keep it wet with fresh stripper during the dwell time if needed.

    Then scrub/agitate, with a white nylon scrub pad (you will need gloves on for this). Try to stick to white scrub pads as the other colours are more course and some may even scratch the slate, also, the colours can ‘run’ on contact strippers. You are aiming to loosen the sealer while is it in a softened state, don’t worry that it is now like slimy soap suds all over the surface. Once you have done this, and BEFORE it has a chance to dry again, use paper towels to pick up all the sludge and dispose. Now apply fresh water, (warm water is better generally) and agitate again with e CLEAN white pad and immediately pick up the rinsing water with a clean sponges. Now finish off with absorbent paper towels or an old terry towel, buff it dry.

    Now, let it dry for a while, it is highly likely you will have removed most, but not all of the sealer – typically there will be some left certainly in the crevices, and the thicker parts. If the sealer layer was really thick, then you might see a slate surface that looks 10 times worse than when you started – don’t despair – this is GOOD – it means that you have broken through about half of the sealer, it is as though you have peeled the sealer layer in half (thick about removing a piece of aged sellotape from a wall, when it does not come off cleanly, instead it de-laminates, leaving half of it’s thickness still stuck to the wall but having removed the surface of it, it now looks dull, opaque, white etc – this is what you have just done to the sealer, but chemically. And the good news is that it is telling you the treatment is working, You just need more of it.

    All that is required is a second go – so repeat the whole procedure. IN rare situations even 3 stripping sessions may be required – just make sure to follow that procedure keeping it wet, scrubbing well, then crucially, rinsing well and drying. Each time you should see an improvement.

    Hope this helps


  17. Hi – I have a honed slate (Vermont slate) in my kitchen. The surface has been oiled with both mineral oil and walnut oil. I’m trying to clean it off. Any suggestions would be hppily entertained. High alkaline cleaner (safe for slate) has been used with some success, but the stones surface is still mottled with some oil (I think). Maybe I need to agitate it but I’m afraid to scratch the surface. Any thoughts?

  18. Hi,

    OK, keep going with the high alkaline. Try it several times, each time it should take a bit more, Try it also with warm/hot water and also try first wetting the stone with warm water to allow it to saturate as much as it can, being slate. Then apply the dilute alkaline cleaner, eave it to dwell then scrub. Then rinse and allow to dry.

    OK if that is not working, try adding some poultice powder (clay absorbent powder, fuller’s earth – diatomaceous earth etc) and sprinkle it liberally on the pre wet slate – it will add some mild (safe) abrasion as well as being absorbent. This will necessitate more rinsing though.

    Failing that, you could try an abrasive cream cleaner in conjunction with your alkaline. Look for Aqua Mix Nanoscrub or there is a MApei USA product called Ultra Care abrasive cleaner I think.

    If you are left with some spots, try using the poultice powder, mixed to a paste and applied over the spots, cover with plastic wrap and leave for 24 hours (I have written about poulticing on the blog).

    Failing that, you could try a solvent based stripper.

    Ultimately though you may not totally remove every last trace.

    Hope this helps


  19. Hi Ian,

    We are in the process of putting naturally split red sandstone slabs (about 1 inch thick) on the exterior of a large square building. We have not finished the project yet, and are coming up with some problems.

    Unfortunately the rough sandstone slabs are now turned a rusted color in some spots after we acid washed it. The rust color is not as prominent when we wet the stone, but still a little of the rusted color shows through. It has been about three weeks since we acid washed the stones. We have not yet sealed the stonework.

    The architecture of the stonework looks like two steps (riser, tread, riser, tread) all the way around the four exterior sides of the building.

    We noticed a day or two after that a rust color was forming on the face of the stone, and also at the grout lines between the stones. We applied the acid as follows: we wet the stone, nylon-brushed on the acid (about one part acid to 3 or 4 parts water), waited about a minute, and then thoroughly washed it off with lots of water.

    Also, some of the grout lines did not come out as clean as we would like (some of the grout dried on top of the stone and ruins the look of the sharp lines between the stone. Do you have any advice for how we could fix this issue?

    Any thoughts or help for how we can return the stones to their natural color, and how we can fix the grout lines, would be greatly appreciated.


  20. Hi Jeremy,

    OK, well you have done what I would have done. I think that the rust coming through might have more to do simply with the amount of water, it is inevitable that acid washing in this way is going to involve a lot of water. If there is a significant soluble mineral content in the stone, then wetting it in this way will provide the catalyst/vehicle for it to come out to the surface as the water dries.

    You do not say what type of acid you use? – But typically I would avoid HCL/Muriatic – it is too strong – better to use Phosphoric acid based products (or similar) they can do a better job removing rust and less damage to the actual grout/mortar joints etc.

    So, you could try more washes (with a suitable acidic cleaner) – it make take a number of attempts in order to exhaust the reservoir of minerals – in other words there will be a finite amount of free iron oxide/rust that can come out of the stone. Also each wash will help to remove a little more of the cement reside from the stone faces, in a gentle way, without causing damage to the jointing itself.

    Other that that, from your address you appear to be in the USA. A US brand called Aqua Mix has (or did have) a couple of products that you might want to investigate: one is a heady duty (but buffered) acid cleaner that is designed to help with red dust type issues whilst at the same time not etching too much of other adjacent materials I think it was called Ex-Treme. Then they also have a product that is a designed to help inhibit further manifestations of mineral efflorescence this was called Eff-Ex.

    Hope this helps


  21. Hi Ian,

    Thank you very much for your quick and helpful reply.

    That is interesting – that the water would act as a catalyst for the minerals to leach out through the stone. We did use a lot of water, and the acid we used was muriatic acid.

    The building is in upstate New York, so we tried a product at our local masonry store called Vana Trol by Sure Klean, and this has taken off a lot of the mortar staining and smears without leaching out any of the rust color. It takes a lot of elbow grease though! Unfortunately it is not really effective at taking away the rust color.

    We are also getting Sure Klean’s Ferrous Stain Remover, which the company said would help to take out the mineral staining. Will keep you posted.

    I hear what you mean by there being a finite amount of minerals which may be taken away by successive cleanings. Already in some parts of the stone we can see how it is returning to its natural color, but others have a long way to go. If the Ferrous Stain Remover doesn’t work we’ll give those other products you suggested a try.

    Thank you very again for your expertise, suggestions and quick reply.

    Best wishes,

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