Zinsser Block Filler 2X is a high-build acrylic primer for interior and exterior residential, commercial, and industrial applications. It has twice the thickness of ordinary primers to fill pinholes and seal voids in concrete block and masonry, resulting in a smoother and more uniform topcoat. It may be applied to new masonry surfaces prior to full 30-day cure. Block Filler 2X seals semi-porous surfaces to provide better topcoat coverage and consistent sheen without pinholing.