old grout, new white "growth"


Old 07-31-09, 01:22 PM
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old grout, new white "growth"

My 1958 split-level is on a slab. Half of the downstairs floor is slate with not-so-thin grout lines. I know it's been sealed, but don't know when or with what. I don't care about the aged, darkening sealant on the slate itself, but I do care about the white powdery stuff showing up in the grout. We've had a tremendous amount of rain and the a/c has been broken. I know that salts/minerals can migrate, but this white stuff is "puffy" in places - mildew? Can I re-treat the grout to stop the moisture from coming to the surface? thanks
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Old 07-31-09, 10:41 PM
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Hi Perrino, I'm not sure about puffy, but otherwise a perfect description of efflorescence. You have lots of water under the slab. You should try to fix that, start outside to improve runoff away from the house. May need a drain field or sump pump? It is not possible to apply something and make this stop. All grout sealers are breathable, they have to be, otherwise the sealer would peel when moisture wants to come to the surface to evaporate. That is exactly what is going on. All you can to is clean it and wait for it to reappear if the conditions do not change. Jaz

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