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Concrete sealer that turns white

by Jodi
(Atlanta, Georgia)

White puddle stains on stonework

Q. We have a flagstone deck and just had it sealed by a contractor. They first painted the sealant on the mortar, which left all of the edges of the stones shiny. They came back and applied the same sealant to the entire deck, but let the sealant puddle in the low places, which left white "stains". It is dry and has white puddles in many places. Is there a way to remove the puddles once its dry? Will they "disappear" over time? It looks awful.

A. There is usually an easy solution for those white spots that appear on a fresh coat of sealer. It's usually caused by moisture getting mixed with the sealer somehow, whether it got rained on or areas of the surface were still wet when the sealer was applied.

Try brushing on some xylene very lightly in a couple spots and see if that works. Xylene is a thinning agent for solvent based sealers and can be found at home improvement or paint stores. If that doesn't quite do it, then apply it heavier and wipe it off. Try this in a few spots first before doing the whole thing.