A gypsum board comprises a set gypsum layer having a first face and a second face. A fibrous mat is affixed to at least one of the faces. The mat comprises a non-woven web bonded together with a resinous binder. The web is composed of chopped continuous glass fibers having an average fiber diameter ranging from about 9.5 to 12.5 .mu.m. The board is exceedingly durable. It has a smooth surface that is readily finished in an aesthetically pleasing way, using paint or other wall covering systems.