Zinsser 1 gal. Block Filler Primer is a high-build acrylic primer designed for interior and exterior residential, commercial and industrial use. With twice the thickness of other primers, it fills pinholes and seal voids in surfaces providing a smoother and more uniform topcoat. Block Filler 2X high hiding formula seals semi-porous surfaces to provide better topcoat coverage and consistent sheen without pinholing. Use on interior and exterior surfaces like concrete, cinderblock, brick, stucco, fiber cement siding, plaster, mortar, concrete masonry units and more to fill and smooth surfaces prior to applying topcoats units. Covers up to 100 sq, ft. depending on application method and surface porosity. Allows for quick project completion: dries to touch in 30 minutes, recoat in 1 hour and apply to new masonry surfaces before 30-day cure of concrete