I’m painting the interior walls of a building w/ latex. There is about 4 ft. of block walls then channeled steel siding above that. There is foam in between the “channels” and the block. The foam is damp and the steel siding is rusted. Can I caulk w/ paintable silicone then paint w/ metal primer before finishing w/ the latex?
If moisture exists on interior surfaces, I would urge you to find and cure the cause of the moisture prior to any coatings or caulk application. My experience in moisture problems is that they must be solved from the outside in.
After you have resolved the moisture concern I would proceed as follows…
Brush off the loose rust. Go to your local paint dealer and ask for a "rust converter." This product goes on with a brush and then is allowed to dry typically for 24 hours. Prime the steel and paint with appropriate finish as recommended by your paint dealer.