What Seals a Basement Wall?

Exterior Sealing

• One method of sealing basement walls occurs on the building exterior. A layer of asphalt is applied to the exterior of the concrete wall to slow the diffusion of water vapor. A waterproof bituminous membrane is then placed over the asphalt, adhering to the wall surface and thus sealing the concrete. This method is used when many small cracks are present and exterior grading is poor.

Waterproofing Sealers

• Home improvement stores often sell do-it-yourself waterproofing kits, which are made from latex-based paints and applied in a similar manner. This type of sealant will work for several years, but eventually the sealant will begin to crack and peel as a result of saponification, which is the leeching of lime from inside the concrete. Waterproofing kits are also ineffective against efflorescence, which is a chalky deposit that forms on concrete walls. Regular latex paint applied to concrete basement walls traps water vapor between the paint layer and the wall substrate, which can also eventually cause blistering and peeling and lessen the effectiveness of the sealant.

Sodium Silicate Sealers

• Professional waterproofing and sealant companies use sodium silicate-based mixtures that penetrate into concrete pores to seal the walls. The sodium silicate reacts with the concrete’s lime content to produce a solid crystalline structure that seals tiny cracks and pores. It also hardens the concrete and makes is denser. When dry, sodium silicate sealer is invisible and does not leave a sheen, surface film or color on the walls. This type of sealant not only prevents water vapor from migrating through basement walls, it also stops gases like radon from entering.

Application

• Concrete walls must be primed before sodium silicate sealers are applied. Because it is applied to bare concrete, the surface must be cleaned of all grease, dirt, oil, adhesive or any other substance that would prevent the sealant from being absorbed. To further augment the sealing process, joints and cracks can be seam taped before the sealant is applied. A garden sprayer, roller or brush is used to apply the sealant after the concrete surface is dampened with water. Two or three light coats, which take about 20 minutes to dry, are usually applied.