I had a relative of a customer of mine call me about a mold problem in her bathroom.
She lives in an ocean front home on a barrier island in New Jersey. She had a leaking shower fixture last year which damaged the green board sheetrock behind the tile and caused the tiles to fall off and mold. The leak was fixed and the green board was torn down for the entire tub/shower. The tile contractor somehow managed to salvage the existing tile. He put up new backer board and retiled the tub/shower with the old tile. He did this so the tile would match the rest of the bathroom.
In less than a year mold has formed in the grout lines in numerous places in the retiled tub. It does not seem to be coming from any one place. In addition, as the mold grows in the grout lines, the tile darkens somewhat. The tub is on an outide wall of the house and there appears to be no external source of moisture to cause the mold. She doesn’t use the shower all that much since it is a vacation home so I don’t think it is moisture from the use of the shower.
My guess (and this is what I want your opinion on) is that there was mold on the tiles from the existing water damage and even though the tile guy cleaned them for re-use, he didn’t kill the existing mold spores before re-installation. Now the mold is reappearing by coming through the new grout. Both the customer and I tried to clean off the mold, but it seems to be too deep to come off with a simple scrubbing or bleaching.
Do you all think my guess is correct? Could there be any other cause of the mold and tile discoloration? Any input is greatly appreciated.
Replies
You can kill mold, but you can't easily kill mold spores; they can suvive extreme conditions.
You also can't have mold growth without moisture. So, find the moisture.
E.g., could it be condensation on a cold wall? Does she keep the heat on with a humidifier, or have another source of vapor in the house which is condensing on the exterior wall?
Sojourners: Christians for Justice and Peace
That's a good puzzle. Perhaps you'll get an opinion from the Russian PM soon. My question is, what are the tiles? For example if they are porcelain, there's no way they could absorb enough moisture to sustain mold themselves, even if the shower is used daily. I suppose they could have 'infected' the backer board but it seems unlikely. If they are soft and porous, there's a chance they could hold water, but it still seems unlikely.
What are the chances that the framing was wet and that the tile guy went right over the wetness without letting it dry completely? Is there a moisture barrier behind the backer board?
It might be worth renting a big dehumidifier and drying out the room. Put it in the shower with the drain hose going down the drain and run it for a few days. Mold can't survive without moisture.
Anyway, let's see what someone else has to say.
I know very little about tile, but if it is a vacation home is it likely that the tile was a simple ceramic tile? The backs of these tiles often don't seem to have a protective seal on them, so could be more porous, giving mold spores a place to rest. What is the pattern of the darkening? Does it look to be coming from the grout, or is there darkness in the centers of the tiles as well (not uniform though, since the tiles are a little thinner at the edges)?
My guess would be that he cleaned the grout off and reused the tiles, but he didn't soak them in chlorine to kill the mold spores. There's plenty of moisture in the mastic to get them started growing, and it doesn't take much moisture to keep them going. We discovered rot in our basement and we live in the desert where it only rains a couple of times a season.