How to Seal Brick and Mortar

by Michael on August 22, 2010 · 7 comments

After moving into our first house, which had an all brick exterior, I was surprised to learn that wind-driven rain can lead to water intrusion through a brick wall. While proper flashing and weep holes should keep this from creating problems, those details are rarely done right.

In our case, the masonry contractor had failed to install the through-wall flashing and weep holes above our walkout bay window. The resulting problem is that water can soak through the brick and mortar and it’ll have no way to get out.

In our case, we ended up with water dripping down into the ceiling over the bay window following heavy, wind-driven rainstorms. Unfortunately, it’s nearly impossible to correct such shortcomings after the fact, as you have to tear out the brick veneer to get at the problem.

How to seal a brick wall

The good news is that, after a bit of research, we found a workable solution — sealing the brick. To seal the brick, we used a product called siloxane (a.k.a. silane), which is penetrating sealer that absorbs into the brick and mortar to produce a water-repellent barrier.

This sort of sealant is different from silicone-based masonry sealers that coat your masonry with a thin film. Instead, siloxane soaks in and partially plugs the gaps in the brick and mortar. The end result is an invisible, breathable, water-repellent barrier.

Siloxane can be applied with a brush, roller, or sprayer. In our case, we used a cheap tank sprayer from the lawn and garden section at Home Depot. If properly applied, the barrier should last 3-5 years. In our case, we moved away after three years and it was still going strong.

How to seal an outdoor fireplace

More recently, we had a new patio installed, complete with a brick outdoor fireplace. Following installation, the mason returned to seal the brick. Guess what he used? Yep, siloxane.

Once again, the siloxane is doing a great job, and not just on the brick… He also used it on the natural stone countertops on either side of the fireplace.

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