I have a l980's house with an add on sun room. The ceiling is a white sprayed on acoustical ceiling (popcorn). The walls are knock down plaster. The ceiling surface and the wall surface meet and no trough was made on the acoustical ceiling to allow painting at the edge. To make a finished look I would like to put molding at ceiling height on the walls which I could paint. What type of molding would work? Is there a better solution than molding? I'd appreciate some ideas to solve this problem.