Hello, I’m renovating an old Philadelphia rowhome that has no insulation on the exterior brick walls.

I bought a DIY spray foam kit (one of those two-tank deals) to add thermal insulation and moisture-proofing to our exterior walls. This is sort of an alternative to retrofitting weep holes, etc.

Underneath the pre-existing mdf paneling (fastened to furring strips), there is old plaster adhered directly to the brick.

My q: does it seem necessary to remove the plaster before installing the spray foam? That is, must the foam be applied directly to the brick? (I’d like to avoid the headache of removing all the plaster before building the stud wall, if possible.)

I think the foam would adhere to the plaster without a problem. The issue is more about the moisture. Would foam adhered directly to plaster trap moisture and possibly lead to mold between foam and brick? Or would the moisture still be able to exit on the brick side? Or does that require weep holes to work?

Any advice welcome.