Last year I set up my NC-30 in the basement and used leftover mortar to make a Venetian plaster look behind the stove. However, the prep work was extremely tedious as I had to remove paint from cinder block. It was OK for that area directly behind the stove, but I really should continue the job around the rest of the room. Mortar won't stick to the painted cinder block. I don't want to spend the jing on covering the wall with metal lath. I'm wondering if I can just rough up the paint with coarse sandpaper then cover it with drywall mud. Would that work?