The back of the flat keystone is crafted to accommodate the profile of moulding MLD215. This creates a perfect customized fit. The flat keystone is basic in form and it becomes a versatile addition to the homes, commercial buildings and structures. Decorative keystones and mouldings are crafted in durable urethane, which makes them exceptionally effective in both interior and exterior applications. The flat keystone is precision-molded. Urethane molds with the traditional detail that makes it a modern favorite. It also remains intact and offers low maintenance solutions. Urethane is non-porous, and this prevents the moisture absorption that can cause warping, cracking and decay. Flat decorative keystones are factory-primed.