Larsen Pwg04 Plaster-weld Interior Plaster Bonding Agent, 1 Gal (Pack of 4) Bonds new plaster to any clean, structurally sound, interior surface High performance bonding of one-coat finish plaster and/or two and three coat work to concrete ceilings, walls, columns, beams, and other structurally sound surfaces Prepares the surface to allow you to plaster directly to concrete over electric radiant heat cable, and to bond cement mortar beds to smooth concrete for installation of rigid foam insulation Can be used over paints having oil, rubber or vinyl bases and over silicone-treated surfaces as well as latex paints Covers approximately 300 to 400 sq. ft. per gallon depending on method of application, temperatures, porosity and texture of the substrate