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by Ron Joseph
March, 2006
Smelly Latex Paint on Concrete Blocks
Q. About two months ago volunteers in our community painted the previously painted
concrete block interior walls at our community center with latex primer. Though
the walls had been previously painted, they still soaked up a lot of paint.
We have not applied the final top coat, so the primer has been exposed to a
cold interior for several months this winter. Right after we painted there was
a dampish odor, but now it has turned into a terrible strong sour smell that
is almost intolerable. Do you have an explation for the odor and its increasing
intensity? If we put on a top coat, will it go away? Should we treat it it any
way before applying a top coat. A. Waterborne paints usually contain biocides to prevent bacterial growth;
however, you wrote that the concrete "soaked up a lot of paint" (and
consequently also water) and "the primer has been exposed to a cold interior
for several months this winter." You are probably smelling the rancidity
of bacteria or mold.
I don't have a definitive answer for you, but in my opinion by applying a topcoat
over the entrapped moisture, you will only aggrevate the problem by preventing
the remaining moisture from evaporating out of the concrete. I suggest that
you use lots of warm air (from heating fans) to drive out all remaining moisture
from the concrete blocks. I don't know if this will totally solve the problem,
but my guess is that it will help get rid of, or at least minimize the odor.
Ideally, you would allow the concrete blocks to soak up a solution of bleach
to kill the bacteria, but I don't think that is practical because you will need
to remove the primer, and then might have problems applying the primer again
at a later stage. If you completely dry out the concrete and if the rancid smell
disappears, then you can consider applying the topcoat.
At the worst you can try to wash a small section of the painted walls with household
bleach and see if that makes a difference. Before applying the topcoat you will
need to rinse off all unreacted bleach with fresh water.
I empathise with you and your fellow volunteers, but this is a problem that
might be difficult to eliminate.
Best wishes,
Ron Joseph
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