I am prepping a wall in my school's library for a mural. It is an interior wall with high gloss paint. I have sanded the wall and cleaned it with soap and water. I used 60 grit sand paper. Can I apply drywall mud directly to the wall to smooth it out for painting. I am planning on applying an acrylic filler primer before painting. Any help will be appreciated.

I took possession of a fixer upper cottage this weekend. After compiling a list of things that need to be done I think my # 1 (for safety reasons) is remediation of the makeshift ceiling that has been installed throughout most of the building. It appears that a previous owner has taken sheets of styrafoam (not proper ceiling pannels) and has attached them to the rafters with pieces of wood trim. I believe the styrafoam sheets are 2 ft X 3 ft. So the ceiling ends up being framed in 2X 3 ft rectangles. I am assuming the sytrafoam is highly flamable and want to fix as soon as I can. I am thinking options may be a) tear down all of the trim and foam and replace with either drywall or perhaps beadboard - this would create a huge mess that I am not particularly keen on and time to get done is another problem or b) put drywall or beadboard directly over the current ceiling so the styrafoam is no longer exposed. Thoughts??