The Crescent-DIY Cast Stone Fireplace Mantel Modern Cast Stone Fireplace Surrounds made out of lightweight (GFRC) Glass Fiber Reinforced Concrete. Our mantels can be installed indoor or outdoor. Offered in 2 different colors Builders, interior designers, masons, architects, and homeowners are looking for ways to beautify homes in their spare time as a hobby or to save on cost. DeVinci Cast Stone has met DIY-ers halfway by designing and manufacturing cast stone mantels with superior aesthetics, that can be easily installed at home with minimal experience, and at an affordable cost.