Context: My house is made of factory built panels made of i-joists filled with dense packed cellulose, sitting on a raft slab. The walls were supposed to sit flush to the edge of the edge of the EPS raft, but a slight change was made midstream in how the panels were made, and they ended up overhanging the raft by a few inches. The bottom of the wall panels are i-joists, with the cavity filled by two layers of fiberboard.

I’ve mulled over and even attempted different ways of covering this exposed bottom part of the wall, and I’ve decided the least annoying way is to put a metal lath (1/4″ hardware cloth) over it and parge it, connecting to the existing parging on the raft. I’m wondering if I have to paint the fibreboard first. If I don’t, the fibreboard will certainly absorb a lot of water, and eventually dry through the vapor semi-permeable OSB into the cellulose. What I’m worried about is whether it’s going to turn the fiberboard to mush in the mean time. Does it even matter if it does? Even if it’s just pulp, the parging should hold it place. There’s not a lot of room to operate down there, and painting it is just another level of crap I’d rather not have to do if it’s not necessary.