Expert: Bruce E. Johnson - 10/11/2010

Question
Hi- I live in a 4 story/6 unit condo building in Chicago.  The building was
built in 1997 out of 8" CMU blocks.  These blocks weren't water sealed, and
now we have water/mold issues on the interior of the building.  Since we are
looking at major work (fix/seal the exterior, rip out drywall on the interior),
we want to make sure we do it right.

My question is what is the best way to fix this?  The building is 8" CMU w/ 1.5"
furring strips, fiberglass insulation between the stips, and then drywall.  
What's the best sealant product to use on the exterior (we've been told an
elastomeric paint).  Would some type of injectable foam be worth putting into
the CMU?  Would this help the water proofing, or just ensure we don't have
condensation forming on the interior of the wall from lack of proper
insulation?

Answer
Hi Todd, yes you can inject the cores of the masonry with foam core fill.  I'm sure that there are several insulation contractors in your area capable of doing this for you.  As far as the exterior goes: elastomeric paint is a good choice for waterproofing but needs to be properly applied to a good substrate and primer.  If the exterior is bare masonry, split faced block or unpainted brick there are some good silicone based sealers on the market that branch chain over minute cracks and poorly pointed mortar joints.  This product requires a certain amount of wall prep and because of the silicone base can't be painted over at a later date.  One problem I can see with your wall construction is the insulation between furring strips.  The best method of furring exterior masonry walls is to sheath the interior of the wall with dense foam insulation board and then shoot the furring strips on top of the foam board using nails capable of penetrating the masonry.  By insulating between furring strips as your original construction you end up with strips of uninsulated wall space where ever the wood strips are.  This could be a cause for moisture accummulation during extreme weather conditions.  I hope this information helps, please feel free to write again regarding this or other matters, sincerly bruce e johnson..bejohnsonconsulting.com