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Can't directly help, but this may be worth reading..: http://landscapejuicenetwork.com/forum/topics/effervesence-in-black...
how long after laying the paving has the sealant been put down? have you got any photos you can put on?
it sounds like you may have put the sealer on too early. there is no way to get rid of the efflorescence, other to let time and nature take its course as the salt crystals need to break down and be washed through. That's why most paving manufacturers recommend waiting at least 6 months before sealing. personally I think longer. I very much doubt you will be able to strip the sealer off, since it is a solvent based sealer and the limestone will soak it through.
Unfortunately the the customer didn't whant to wait plus me saying I can't finish your patio for 6 months doesn't go down well.
A before picture even though it's been sealed 3 times, the other is a picture once it's been pressure washed And has the look I'm after
Customer expectations again. Glossy pictures of black and white contemporary styling have a lot to answer for.
Have been involved with 'black' limestone paving once before and that was to remove it; its not black and when sealed tends to show all sorts of marks.
Sorry I cant be more positive.
well there going to have to wait now! the salts will break down, but it will take longer. Did you explain why they needed to wait? i assume you did from your comments, so their impatience appears to have got the better of them. It doesn't actually look too bad in teh photo. it will go, but there's not a lot you can do to apart from letting mother nature take her time
Part of what you do needs to be giving advice, and sometimes it means telling it like it is, even if its not what they want to hear. if they need to wait, they need to wait. Got to agree with mike, so many people choose it because they think its jet black and then get dissapoinited when it turns to a grey in a year or two
its the wrong product to seal limstone, should have used lithofin stain stop or romex stain stop, that stuff will be very hard to remove and make right. contact roger okley at R&A pressure washing he is one of the best men in the job to advise you google him
Bit late to reply on this one, not being on ljn for a while. Hope everyone is having a good summer?
Roger is definitely the man to speak too on this. Stripping off the sealant is an expensive process that involves using some heavy chemicals.
To expand on what mark said about the wrong sealant being used. If an impregnator is used then it can be applied immediately after the patio has been installed (as long as it's dry). Impregnators allow the stone to breath by coating the capillaries of the stone with a water repelling chemical. This allows efflorescence to escape in the form of vapour.
In this case a topical sealant was used. Topical sealants operate on the surface of the stone and literally seal the whole surface of the stone preventing any moisture from going in or getting out. Hence they trap moisture in the stone. Topical sealants are old technology and should never be used on natural stone.
The particles in impregnators are much smaller and this allows them to soak into the capillaries of the stone. The particles in topical sealants are much larger and can only operate on the surface of the stone. Because they operate on the surface of the stone, topical sealants also break down much quicker and need re-applying every couple of years. Unlike impregnators which can last up to 15 years.
Steve
If you want to learn more about what Steve London Stone is talking about then you'll find a wealth of advice and experience on pavingexpert.com.
I've just been trying to get marks off some grey sandstone that I laid. Some are cement and ? SBR stains from a scruffy renderer who isn't taking responsibility, some may be natural brown stains due to efflorescence or I know not what.
I tackled these with regular brick acid (diluted then neat) Lithofin Wax off (for wax, oil tar etc) and Lithofin Cement Away (also acid - cement, rust..). The acids only tackled the cement but also started dissolving the pointing. The Wax Off was of no use.
Good luck with your problem.
Chris, take care using acid on grey sandstone. Grey sandstone has a high mineral content and sometimes using acid can bring out orange rust marks on the surface of the stone.