A.Henri de Marne,
a Waitsfield, Vt., consultant on wood-frame
construction problems, responds: The reason
that the new mold is at the base of the walls and
in the corners is because these are the coldest
areas and because the air is stagnant in spite of
the fan you installed. There is basically nothing
wrong with what you did, and not killing the mold
on the masonry walls is not what caused the new
mold on the drywall; the mold on the concrete could
not grow through the fiberglass insulation and the
plastic vapor retarder.
However, I think it was a mistake to install a
fan. This obviously requires an air inlet
(generally on an opposite wall) and both are most
likely in window openings high up on the wall. This
has the effect of bringing in a fresh supply of
warm, moist air without creating air movement where
you need it most — at the base of the
walls and in the corners of the room.
It would be better to close all windows and
doors to the basement during the hot, muggy summer
months and run a dehumidifier with a humidistat.
This will remove unwanted moisture from the air.
There is no harm in circulating air within the room
with a fan, and the owners can still open the
windows for natural ventilation on dry, breezy days
if they wish. You should kill the mold either by
spraying the moldy areas lightly with a mixture of
equal parts water and fresh Clorox bleach or by
rubbing them gently with a sponge dampened with the
It would have been better to adhere rigid
insulation over the entire concrete wall surface,
then install the furring strips, to avoid the
thermal short circuits now happening through the
For the pony wall, instead of using studs and
fiberglass, why not fasten a layer of 2-inch rigid
insulation over the existing drywall as a
wainscoting, then cover it with drywall or paneling
and top it off with a display shelf?