Diagnosing the problem
1 of 2
Photo 1: Plastic test
Tape plastic to the concrete floor
and leave it for one day.
2 of 2
Photo 2: Evidence of a problem
Remove the plastic. Water droplets
and a wet floor indicate moisture is
coming through the concrete.
Moisture from the damp ground
outside is probably coming
through your concrete floor and walls.
First look for visible signs of moisture, like
damp concrete along the walls and white
lines of a powdery substance on the walls
themselves. The powdery material is
called efflorescence, which is finely crystallized
minerals that are deposited as
water dries out. If you don't spot these
signs of incoming water, duct-tape a 2-ft.
square of plastic (a plastic garbage bag will
work) to the floor near an outer wall and
another to the lower half of the exterior
wall. Wait 24 hours, then remove them
(Photos 1 and 2). If the concrete under
them looks dark and damp or you find
moisture on the underside of the plastic,
moisture is coming through the concrete.
You should be able to control the
dampness and odors by running a dehumidifier.
The musty smell is caused by
fungal growth, so you may have to scrub
the walls, replace damp boxes, and wash
or throw out musty-smelling items. Store
items on blocks or storage racks to keep
them off the floor.
Unfortunately, there are no easy fixes to
stop the moisture itself. Older basements
were not damp-proofed on the exterior as
they are now. And applying a dampproofing
sealer to the walls and floors on
the inside may work for a while but isn't a
However, sometimes small changes
outside can have a surprisingly large effect
inside. The key is to channel rainwater
and other moisture sources away from the
foundation. Make sure your gutters aren't
clogged, your downspouts dump water at
least 6 ft. away from the house and the
ground slopes away from the house.