Hey Gary no offense meant, I appreciate any and all suggestions.....LATICRETE 50 Lb. Multi-Purpose White Thin Set was what I was looking at, I'll read the sheets on your recommendation thanks! Ace I'll read up on that "flex-bond" too....thanks! The only thing i actually used different was the .020" stainless sheet over the rear wheels and engine area, up to and including the area above the batterys and fuel tank compartment! Prevost did the same to protect the floor material from road and weather moisture! It is the bottom layer of my built up floor! This sheet completely seals the back of the bus from wall to wall!