How to Seal Brick and Mortar

by Michael on August 22, 2010 · 8 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.

{ 8 comments… read them below or add one }

Dan September 28, 2010 at 12:11 pm

Michael, we are having the same exact issue with our bay windows and have done everything else except this. It is comforting to hear of someone who found a workaround. Is the product that your talking about made by Proseco?


Michael September 28, 2010 at 12:46 pm

Dan: I’m not at home, so I can’t check. However, I just Googled it and the label on the Prosoco (not Proseco) brand looks just like the jug that we have at home, so I’m pretty sure that’s right. Good luck.

P.S. We moved a few years after we applied it to the wall above the bay window, so I’m not sure how long the protection lasts. You’ll probably have to re-apply at some point.


Dan September 28, 2010 at 11:46 pm

Michael, thanks for the response. We have been fighting this leak for over a year. This is our first home and we have done everything. We replaced the copper roof over the bay windows, we sealed the windows on the second floor with NP1 caulking, there are not any cracks in the bricks- and every contractor that has come out has no clue… Its like they cannot fathom the idea that water can get through the mortar joints. So this issue here is probably no flashing behind the brick right? When they built the home and did the brick work they probably did not put any kind of membrane system to direct the water away from the bay ceiling. That is where we are getting all our water (in the bay ceiling of the first floor.) The siloxane is really our last option now- unless we want to spend over $10,000 to rip off the bay roof and the brick to put the correct flashing. Do you think we probably are having the same issue you had at your previous home? If so we really feel confident about the siloxane! Thanks again. We are really at our wits end after fighting this nightmare for over a year now. Dan


Michael September 29, 2010 at 9:07 am

Dan: Let me preface this by saying that I’m far from an expert. Just a homeowner who’s dealt with similar problems in the past. In other words, take what I say with a grain of salt. 🙂

We didn’t have another window above our bay, so it seemed clear that the water intrusion was happening through the mortar joints. If you have another window up above, it’s always possible that water is getting in that way even if you think you’ve sealed it up tight. Or maybe it’s somehow getting in at the top of the wall and then working its way down? Roof leak? Since the siloxane isn’t all that expensive, it’s probably worth a shot before you do anything drastic. You can apply it with a tank sprayer like you’d use for lawn chemicals. Just be very careful if you have to go up a ladder to do it. We actually hired a handyman to do the job – in fact, the siloxane was his idea.

I’m curious, does this happen every time it rains, or only during major storms with heavy rain and wind form a specific direction? The other clue for us was that it only happened in major, wind-driven rainstorms with the wind coming from a specific direction.

As for the cause, yes, I believe that in our case it was due to a lack of flashing where the brick met the roof of the bay window. It’s impossible to know for certain without tearing the brick off, but it seems that brick flashing, along with other waterproofing details, are rarely done right nowadays.

Best of luck.


Dan December 10, 2010 at 6:55 pm

We are about to apply the siloxane! Hopefully this will solve our issue. To answer your question… Yes, this only happens during a wind driven rain blowing hard from the east. We get no leaks at all during a normal strait down rain. It sounds like your exact same situation.. I really hope. Thanks again for the advice and for creating this post.



richard January 11, 2012 at 11:20 am

Let’s say I had a brick structure where the brick and framing walls are sitting on the same foundation level and there is no weap holes. Would it be advisable to make some or would that allow water to get in from there as well. The building is an older commercial structure with the blacktop parking lot going right up next to the wall


William February 11, 2012 at 8:57 pm

Our neighborhood has a brick and mortar monument at our entrance whihc is 35 years old. Several years ago someone hit the monument and we had to have the front section rebuilt. The new mortar is glaringly bright compared to the old mortgar (I feel the mason should have foreseen this and colored the new mortar). Someone suggested appliying a sealer to the entire monument to achive a better matched mortar color. Any thoughts? Thank you.

Reply skins mod list June 5, 2016 at 4:51 am

On clicking on the down load button they may redirect that
you another site which is with your no make use of.


Cancel reply

Leave a Comment

Previous post:

Next post: