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USG Durock™ Brand Surface™ and Surface™ FR Self-Leveling Underlayments are pre-sanded engineered cementitious underlayments designed by USG for interior use in commercial, institutional and rehab construction. USG Durock™ Surface™ and Surface™ FR Self-Leveling Underlayments provide a smooth, hard underlayment surface over concrete slabs, pre-stressed concrete and concrete planks at thicknesses up to 3 in. (76 mm). Suitable for a variety of floor coverings, USG Durock™ Surface™ and Surface™ FR engineered cementitious underlayments exceed commercial vinyl floor-covering requirements as a high-performance underlayment with compressive strengths ranging from 4,500 to 5,500 psi (31.0 to 37.9 MPa). USG Durock™ Surface™ FR Self-Leveling Underlayment is reinforced with fibers that improve impact strength. It is a cost-effective solution for interior use in commercial, institutional and rehab construction. USG Durock™ Brand Surface™ and Surface™ FR Self-Leveling Underlayments may assist in obtaining LEED credits 5.1 and 5.2.