Re:Theroretical Drywall Question? 4

July 6, 2008

Todd,

The discoloration is probably just house dust that was trapped from

small air flows by the roughness of the surfaces. (This is commonly

seen at the edges of light-colored carpets.) If you are worried about

it, I would agree with Carl that tape sampling would supply the answer

to your question. Be carefeul where you send the sample. One lab

identified soot, a possibility if you burn jar candles, as

Stachybotrys mold!

I would disagree with Carl's expert about drywall. There are millions

of homes and commercial buildings that have been built with drywall

where walls and ceilings do not have mold problems. Lots of folks even

put wallpaper (with starch glue!) over plaster walls to no ill effect.

Mold grows because of excess dampness, whether from leaks or high

humidity. You don't even need paper for this to happen. Mold will grow

in settled dust on steel and glass if the humidity is high enough. And

dust is everywhere. This is why mold grows on foundation walls in

basements and in carpets on concrete. Neither concrete nor plastic

carpet fibers are biodegradable, but the dust is.

So the key is to monitor the relative humidity. Therma-Stor now sells

an " Alert " thermo-hygrometer that measures temperature and relative

humidity (RH) and records the hours the RH is above a value that you

set; it even rings a small alarm if the RH exceeds the preset value:

You can place one of these for a few days or weeks where you have

concerns and see what is happening. Most molds can't grow under about

75% RH and don't really grow much until the RH is over 80%.

Don't be confused by other advice I and others have given about

basement RH, as

you will hear that 50% RH is a recommended indoor value. This is

because you want a large safety factor in the air; keep in mind that

if the RH is 50% in the middle of a basement, it is likely to be

higher at the cold foundation walls near the flor because RH INCREASES

as you cool air.

Some " green " builders are constructing houses with straw bales! (The

first one was torn down after several years due to mold growth!)

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