Q: We bought a 50-year-old house last year. The bathtub is along the outside cinder block wall, which has a glass block window. The problem is that where the window sill meets the window, there is a gap that goes behind the wall, which was never caulked. During showers (the previous owner took baths), water goes behind the ceramic tile. I've tried a do-it-yourself mold test, which did not show any abnormal readings, but I've had two mushrooms grow out of the wall. We're going to remodel this bathroom and I'm worried that there's mold in there. What do we do if it's there?

A: If the house has plaster interior walls, you may be in luck. Plaster has few nutrients that will support mold growth. The outer walls, I presume, are the concrete blocks and they also do not have nutrients that will support fungal growth. Deposited dirt on either the insulation, or surface of the plaster/concrete will support mold growth. If the walls are plasterboard or gypsum board in the wall cavity behind the ceramic tile, then the paper facing of the wallboard can grow mold.

The “mushrooms” are a mold named basidiospores and they likely are growing from the wood framing. The presence of the mushrooms indicates chronic water exposure has occurred. Generally, mushrooms are not a mold that is considered to toxic; nevertheless you should not eat them and they can spark allergic reactions.

I would suggest that the bathroom be sealed from the rest of the house during the demolition and ideally a fan be placed in the window to isolate it from the rest of house with negative air pressure, particularly if the house is occupied during the remodeling. The laborer doing the demolition of the wall should wear a respirator (N95 type) when doing the work. If significant mold growth is discovered when the wall is opened, then the laborer should stop and a professional mold remediation firm should be called in. They will have more effective engineering controls to contain dust and they will have trained staff in the safe removal of contaminated building materials. They should be able to treat wood framing that has mold growth but is structurally intact. In addition, depending on what you know about the house, you might want to test the wall for asbestos content.

Fifty, years ago it was possible to find asbestos in plaster and joint compound. Mold remediation is not a regulated area at this time, nor is there a licensing procedure available. The U.S. Environmental Protection Agency (www.epa.gov) and others have guideline documents and some private groups have “certification” procedures. Conservative precautions may be balanced by the additional costs they incur. A careful but reasonable approach is suggested, keeping in mind that safety should be a primary requirement, not costs.

Thanks to Mark Goldman, who is a senior air quality scientist for Engineering and Fire Investigations (EFI), a firm that provides mold investigation and indoor air quality services nationwide. Mark can be reached at mark_goldman@efiglobal.com

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