F4 Calcium carbonate Omya Extenders / Fillers >> Calcium Carbonate, ground Extenders / Fillers >> Limestone Silyl-modified polymers PU - Prepolymers SEALANT Novel developed functional and economical fillers, based on natural calcium carbonate (GCC), were studied in silylated polyurethane (SPU) sealants. All fillers are surface treated with stearic acid. F4 GCC Limestone Limestone. Possesses surface treatment with stearic acid. Used as a filler in silylated polyurethane (SPU) sealants.