Block Basement Moisture: Helpful Advice & Tips from The Basement Builders
Q: We want to finish our basement. What can we do to keep moisture away from the walls, and what should we use for a subfloor?
A: Finishing a basement is one of the best ways to increase living space in your home and typically gives you about a 79 percent return on your investment. One key issue you need to consider when finishing a basement is how to block moisture.
Moisture can quickly turn your dream space into an expensive nightmare. Condensation occurs when the basement is cooler than the rest of the house. This happens when the temperature difference is greatest between the cool basement air and the warm outside air.
Another cause of moisture in the basement is improper grading against the exterior of the foundation. Adding a sump pump in the utility area of the basement will keep water from entering your living space. Fill cracks, holes, and expansion joints in the floor with a vinyl or cement-base floor-patching compound. You may need to apply a floor leveler if the existing concrete is particularly rough or uneven. A basement subfloor will give you a flat, level surface that is more comfortable and warmer than concrete.
The easiest method for applying a subfloor is to use a subfloor panel system. Otherwise, follow these steps: First lay a plastic moisture barrier over the concrete. Then create floor joists by laying 2x4-inch pressure-treated lumber flat and securing the boards to the concrete with a power-actuated nailer or masonry screws. Place 3/4-inch tongue-and-groove plywood on top and secure it to the joists to finish your subfloor.
Seal concrete block walls by coating them with masonry waterproofer, adding a vapor barrier, then adding wood framing. An efficient vapor barrier has a vapor permeance value of 1.0 or lower and includes plastic sheeting available at most hardware stores. Attach 2x2-inch furring strips with masonry nails in the mortar joints or self-tapping masonry screws through predrilled holes. Then attach 2x4s to the furring strips, insulate the stud cavities, and put up another vapor barrier.
If you are a do-it-yourselfer, hopefully this information can guide you in the right direction. If you want professional results, then contact The Basement Builders. We LOVE basements so much, some would have us 'committed'.