This is a tricky one. We laid a black limestone patio about 80/m2 4 years ago. We were asked to clean & seal it with polyurethane seal, which we did in February. Immediately after the sealing the paving looked as good as new. However, since then it has developed a mottling pattern like a dalmation dog which are random & milky in appearance. The sealant is a tried & tested top quality product. It looks like we had sealed some moisture into the paving although it was quite dry when we did it. I was told acetone would remove the sealant & clean the paving at the same time, which is what we did. This seemed to result in a white bloom coming out of the paving, again randomly, so that some slabs seemed more white than black. We pressure washed it again which seemed to remove some of the residue & again washed it with acetone & cleaned it. This made a slight improvement. At a loss as to what to do next we sealed a couple of slabs to see what happened. That seemed to have worked so the rest was sealed. Since then this milky mottling has been appearing. In my experience it would appear to be effervessence. I have talked to everyone I know & have gleamed little as a result, people just don't seem to know a course of action.
I am now left with a situation where the paving is undeniably mottled. I have to come up with an answer, hence this posting. Unless I can find a solution to removing the mottling I either have to find an acceptable paint (if one exists that is acceptable), or potentially replace the paving.
Anyone have any experience regarding this?
Regards, Duncan Ross www.gardendesignco.com
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Replies
Oh dear this sounds awful. The mottling you describe sounds like the sealant reacting with moisture.
Who told you to use acetone as I'm not convinced simply cleaning with acetone would remove a quality polyurethane sealant. I've never done it but as far as I know its a proper nasty chemicals job.
I would guess that you now have a situation where some of the sealant remains but some is damaged or deteriorated by the acetone hence the patchy appearance but honestly that's just a guess.
If you get no joy here heading over to the brew cabin forum on paving expert may be a good idea as its obvoiusly paving centred
Email me some pictures across and I will get my contact at dry treat to take a look at it. Hopefully it's going to be fixable
steven@londonstone.com
Cheers steve
david.coster@drytreat.com
without wishing to state the obvious, have you spoken to the technical department of the sealant manufacturer?
sounds like s good idea to me!
Thermo said:
Hi Duncan
I have spoke to my contact at Drytreat and he has advised me of a solution to sort out your patio without relaying.
You will need to remove the old sealant. Take advice on how to do this from the sealant supplier, but going on your orignal post i beleive they have reccomended acetone.
Once this has been done, re-seal the paving withb Drytreat colour enhancing sealant. This is not an impregtnator so will require re-application every 3-5 years. We recently had a phonecall from a cleint whose builders had used an acid wash to remove mortar from blaack limestone. The result was much worse than yours, the whoe patio turned a chalky white. We carried out the solution reccomended above. See the before and after shots below. Pictures are a little small but gives the general idea
Hi Duncan
Have a look at my previous post on using sealant at high temp. the surface temp of black stone in the sun can be very high and may of resulted in baking the sealant on the surface before it could penetrate,
Tim