Hi, I wonder if somebody could help me please. We have just removed the wallpaper from a room with the intention of painting it and found a bricked up hole above the door. It looks like somebody has just used cement but we need to get this smooth so that we can paint the room. Is there a product we might be able to use for this (stronger type of filler or something?) that could be sanded smooth, or is it something that requires a professional to plaster over it? Thank you very much for any advice.