Expert: Dan Griffin - 1/2/2010

Question
Mr. Griffin,

My home is 5 years old and it was built in Southern Maryland with poured concrete walls.  Now I am ready to finish my basement, but the dilemma that I have is whether to drylock or not.  I have no evidence of leaks or anything, but I do run a dehumidifier due to moisture smell during summer and fall, but not too much in the winter, and I do understand that concrete is porous, so water vapor emittance is normal. My co-workers strongly advised drylocking the walls, but to do so I must take all the builders hung insulation blankets down to do so, not that this is a problem, I just want to go about the process smartly, while not wasting a lot of time doing things in the end proves to be a waste of time. Please advise on the need to seal my walls prior to beginning the framing process.

Thank You!

Thomas

Answer
Thomas, basements can be so problematic that I think I would take the "belt and suspenders" approach.  Do everything that you can to prevent potential problems.  We both hope that your builder already did a good job of waterproofing or damp proofing the exterior of your basement and installed a perimeter drain and/or a sump system.  I personally would use Xypex over the drylock.  I would also avoid using any finish on the floor that can't breathe.  I would include a dehumidifier in my long term plan in the basement.  I don't know how the builder had the insulation installed, but I would prefer seeing an air gap between the concrete and the insulation.  I would also space the bottom plate off the floor with treated wood blocks to allow some air and allow possible future moisture out without damaging materials and give the earliest possible notice of a problem.

There are many approaches to insulation in basements.  I prefer:
Water treatment of concrete
Installation of rigid foam
Layer of vapor barrier
Air gap
wall assembly.

Review these sites;
http://www.buildingscience.com/doctypes/designs-that-work
and
http://www.fcs.uga.edu/pubs/current/B924.html

to help make your own decision.  You might also ask a local contractor who knows your area.