Should I seal the brick on my Ottawa house?

Sealing brick is a decision worth pausing on, because a sealer can cause the very damage it seems to prevent. A National Research Council building digest (CBD-30) explains that with a vapour-permeable but water-repellent membrane on the outer face, salts are deposited behind the surface layer and the resulting force of crystallization can cause the skin to spall.

What that means in practice is that the condition of your brick and mortar matters before anything goes on the wall. So the question is not simply whether to seal, but what is actually happening with moisture in your wall.

A few things worth knowing before you decide:

• CBD-30 also notes that salt spalling is very similar in appearance to frost damage, and in many cases it is difficult to determine which mechanism caused it. A mason looking at the wall can say more.
• CBD-30 notes the risk specifically with vapour-permeable water-repellent coatings; the behaviour of other sealer types is not covered in the same digest.
• If the property is designated or in a heritage conservation district, the Centretown and Minto Park district plan says painting brick or stone is not appropriate, and the Wilbrod/Laurier plan says existing unpainted brick should not be painted. A sealer is not paint, but any treatment that affects heritage attributes can require approval; check your district's plan or contact the City's heritage staff.

Ask the mason before applying anything to the wall. A mason who has looked at your brick can tell you whether the joints are sound, what the moisture source is, and whether a coating makes sense for your situation. That conversation is the right starting point.