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effervesence in black limestone
Posted by duncan ross on April 17, 2013 at 17:16 in Hard landscaping and paving products
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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