The 8-foot lengths of extruded polystyrene are topped with fiberglass and a thin coat of acrylic plaster. It's light and flexible as wood, as seamless as solid plaster, and DIY-friendly; joint compound holds it in place and fills seams. Like plaster, it has to be painted.
Stock profiles range from about $1.80 to $7.75 per linear foot.Shown:
6-inch-high CTR-813, about $4.10 per linear foot; Canamould Extrusions
(Go here to see how Canamould is installed