Published on February 23rd, 2015 | by Henri


Condensation leaks from new concrete porch

Q.  We added a room and porch to our house last summer. The porch is covered and the room beneath it is heated. The porch is cement and the problem is that it constantly leaks water. I have 2-inch thick Styrofoam insulation on the ceiling of the room, but as soon as you touch the boards, water runs off. Is there any way to prevent this water (condensation) leak?

Also, the outside walls are split-faced blocks, which were painted red and over the summer white has run over the painted surface. I am not sure if this is from the mortar or the blocks. Can anything be done to prevent this from happening again if we re-paint the split-face blocks?

A.    If the concrete porch floor was poured onto a ribbed steel form, the rigid Styrofoam insulation boards cannot prevent condensation from forming. To be effective at preventing condensation, the Styrofoam would have to be glued tightly to a smooth concrete surface. The best solution may be to replace the Styrofoam with sprayed-on, closed-cell polyurethane insulation, unless you have a way to inject canned foam into the open slots until you fill them completely.

If the white you mention on the red-painted, split-faced blocks is powdery, it is efflorescence, and it is caused by salts in the masonry leached out by moisture, which leaves the salts high and dry after the water evaporates. Remove it with a stiff bristle brush. Solving the condensation problem may also eliminate this one if the excess moisture in the room is absorbing the salts and moving to the outside.

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