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Negative-Side Sealant

On a foundation, the "negative side" is the side of the basement walls on the inside of the house.  Because foundation walls are made with porous concrete and grout, moisture is continually being absorbed from the moist earth outside of the home and through the concrete.  As this moisture reaches the surface of the concrete, it's absorbed into the basement air.  This transforms the basement into a humid environment, which makes it an environment where mold, must smells, and dust mites can thrive.  Additionally, the humidity will spread throughout the house and increase heating and cooling bills.

To solve this, many basement waterproofing contractors will offer to apply negative-side sealants to the concrete basement walls.  At a glance, this is a very appealing and sensible solution to many homeowners.  The logic behind this is that a special waterproof paint or hydraulic cement will create a vapor barrier on the basement walls that will prevent moisture from traveling through and passing into the air.  It's cheap and it sounds good.

Unfortunately, negative-side sealant does little to help with a wet basement.  No matter what technique you use on the basement walls, these seals treat the symptom and not the problem.  In time, hydrostatic pressure pushing water vapor through the concrete from the other side will cause the paint to peel, blister, and flake off the wall.  Hydraulic cements used to seal leaking wall cracks form an inflexible barrier on the walls that results in new cracks forming around the seal and nearby as the walls naturally flex with moisture and temperature.  Because negative-side sealants do not remove the water sitting around the foundation, they will usually fail within the first couple months or after a heavy rainfall, allowing this water sitting against the foundation to find its way into your basement.