Expert: Bruce E. Johnson - 10/14/2008

Question
I have a wall assembly that is made up of 8" concrete block that has smooth stucco exterior finish that has recently been power washed and painted.  The interior of the block has 1/2" sheet rock adheared to the block.  The block is raw ( no sealer, no paint ).  The walls were recenlty covered with wall paper.  Light pink bloches have appeared on the wall paper in various areas.  I took off the sheet rock and there was some black mold.  I'm ready to remove the sheetrock and replace it but should I seal the concrete block or apply a layer of plastic onto the block wall or prime the back side of the sheetrock?

Answer
Hi Chris, preventing water intrusion always starts at the exterior first.  You need to have a good paint job on the outside to stop water from getting inside.  That said, I don't like the idea of gluing drywall directly to masonry.  I think furring strips of 1x2 or 1x4 attached to the block and then the drywall attached to the furring strips is a better practice.  The furring allows any small amounts of moisture to evaporate within the wall cavity.  If you are going to go back to direct drywall to masonry then you should use a densglass drywall.   It doesn't have paper backing which gives mold something to live on.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com