Guess I'm not old enough to know what these old congo walls are. Please describe them. I envision an rental house in Africa or else someone put congoleum floor covering on the walls.
Any smooth or slick surface will benefit from a sanding to rough it up so the paint will bond and then use a couple coats of primer like Kilz before the paint. I don't know what the end result will be or how long it will stay on before peeling and chipping since I don't know what congo walls are. But some people(?) paint things like formica countertops, wood wall paneling, brick fireplaces(then cry when they can't get it back off), etc. even though conventional wisdom says it not the best thing to do. But who am I to argue with the cute and weird interior decorator on Trading Places who wears a blouse 2 sizes too small. She had this commercial for her show and said "who decorated this mess?" I believe it was her and her pink and purple rooms, etc.