I have a fully-covered first floor deck with floor about 3-4 feet above ground level. There is old steam heating pipe network extending to a radiator on the deck. The deck is made against a brick building facade, so the inner wall of the deck is all [painted] brick (up to foundation stones starting some short distance under the deck floor). While the deck is pretty well sealed on 3 other sides, the 4th side that's against the building itself has a gap of up to 3/4" between the brick wall and the floor of the deck. The floor has very old wooden boards which were a few years ago covered with carpeting.

While it's tempting to just use spray foam to cover that gap from drafts and any occasional insects, I'd like for it to be a more thorough seal, particularly if a rodent ever gets under the deck from outside. My current thought is to use copper mesh I already have on hand, stuffing it all along the gap, and use *some compound* to impregnate the mesh and go on top of it. The compound is what I am unsure of. Can it be any good caulking/sealing compound? Or should I go for something more heavy-duty like mortar? Or perhaps spray foam through the copper mesh is still a fine way to go?

What would you recommend in this case?