Patching spalled brick instead of replacing it in Ottawa, okay?

Patching over a spalled face is not the same repair as replacing the brick, and whether it makes sense depends on how much of the face is gone and what caused the spalling in the first place.

A National Research Council building digest (CBD-30) notes that salt spalling "is very similar in appearance to that produced by frost action, and in many cases it is difficult to determine which mechanism has caused it." That matters here because a patch applied over a brick that is still absorbing water or cycling salts may not hold. The digest also cautions that a vapour-permeable but water-repellent coating on the outer face can cause salts to deposit behind the surface layer, where crystallisation pressure can cause the skin to spall. So the cause of the original damage shapes whether any surface treatment makes sense.

What to ask for in writing before any work starts: which bricks the mason proposes to patch versus replace and why, how the mason will assess whether the remaining brick face is sound enough to hold a patch, where matching replacement brick comes from if full replacement turns out to be needed, how mortar colour and joint profile will be matched on any replaced units, and how silica dust will be controlled during any cutting or grinding work.

Before committing to a patch approach, ask the mason to explain what they will do if the patch fails within a season, and get that answer in writing as part of the warranty.