What Kind of Sealant Do I Use on Damp Brick?

Surface Sealers

• Most sealants designed to help brick walls stay dry so paint adheres sit on the surface of the brick instead of soaking into it. These sealants use wax, resins or urethanes to create a film over the surface. Some brick sealers don't allow air to travel through them. This may sound good for a water-proofing coating, but this traps moisture inside the brick. The right brick surface sealants allow moisture to evaporate out of the sealant without letting more in.

Penetrating Sealants

• For more serious brick wall moisture problems, you'll need to coat the masonry with a penetrating sealant. Siloxanes and silanes form the base of these products. These two chemicals penetrate beyond the surface of the brick. This creates a very water-tight seal that keeps moisture from soaking through the porous material. Cracks or problems with the mortar between bricks will allow the wall to become damp again even with these kinds of sealants.

Mortar Sealants

• Cracks and openings occur in the mortar between bricks due to weathering or slight shifts in the wall itself. Sealing these openings keeps the wall dry, but also helps lower energy bills by stopping air drafts that make your heaters work harder. Mortar repair products work best for large cracks and gaps. The same silane-based sealant used for bricks penetrates mortar as well and works to seal hairline cracks or overly porous mortar mixtures.

Other Repairs

• Sometimes sealing bricks isn't enough to stop a dampness problem. Rising dampness comes from where a wall meets wet soil and wicks moisture upward through the small openings in the bricks. A line of very hard, water-proof bricks should be installed at the base of a wall to prevent this problem. These bricks prevent moisture from rising, but with age they crack and become more porous. Replacing these bricks is difficult and the only solution for rising dampness in a brick wall.