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More on Mold

In the June Q&A column, Mac Pearce advises soaking the wood in a bleach bath. Bleach does not kill mold — that’s a fallacy. Maybe it used to, but just as bacteria have become resistant to antibiotics, mold has become resistant to bleach. Even the EPA discourages the use of bleach to kill mold. Secondly, Mr. Pearce states that fogging is ineffective against mold. Again I disagree. I have been using two antimicrobial agents, Anabec and Benefect; I spray them on mold-covered surfaces, and they do kill the spores. We have also successfully used a cold plasma process in fire-restoration jobs to eradicate mold and odor without demolition.

There are new technologies available to us and it is time to stop using outdated and ineffective methods.

John DeCiantis

Stonington, Conn.

Mac Pearce responds: The bible of sanitizers is Seymour Block’s Disinfection, Sterilization, and Preservation. In the chapter on chlorine disinfectants, there’s a graph that shows that bleach does not kill some kinds of mold spores. But what bleach does do is remove mold from surfaces. Dead or alive, the stuff comes off with scrubbing, 15 minutes of wet contact time, and a thorough rinse. I have grown mold on hundreds of test scraps of drywall, then treated them with straight bleach. After scrubbing and rinsing, the mold is gone. I’m not sure where the government came up with its anti-bleach conclusions; all I have is my own experiments to go by.

Fogging has the opposite result. It may kill the mold, but it doesn’t remove it. Fogging is an inviting choice for mold growth in hard-to-access areas, such as wall cavities. If it worked, you wouldn’t have to open up the wall to get at the problem. But in my opinion, mold is an irritant — dead or alive. Fogged mold may be less irritating, but unless the treated surface is rinsed off, the mold is still there when the fog clears. In my opinion, fogging moldy surfaces is a poor substitute for a proper repair.

I’ve been doing mold analysis since 1992. I’ve investigated thousands of homes and buildings and have collected tens of thousands of culture plates, almost all of them analyzed by me. I certainly don’t claim to know it all — these are my opinions, based on my experience. The fact is that there has been almost no unbiased research on moldy construction materials or mold removers that is of practical use to builders. Every product salesman has some sort of data to prove that his product is the greatest thing since the can opener, but it’s hardly surprising that a researcher hired to test a product made by the company that is paying for the research has a strong inclination to show that the stuff passes the test. It isn’t even necessary to fudge the data; if you set up the right test conditions, you can get the results you want every time. Over the past 20 years, I’ve seen a lot of quackery and many bogus products related to moldy buildings, so I tend to be skeptical.

Field Guide Correction

Alert reader Eric MacLane wrote to inform us of a mistake in the JLC Field Guide, Volume 1. The correct instruction for Figure 1-2, which provides the square-foot area coverage of a cubic yard of poured concrete for walls or slabs of a given thickness, is to divide by the coverage factor, not multiply. Field Guide users can download an errata sheet with the corrected table (shown here) from