Block Out is a modified synthetic primer sealer carried in a special solvent that dries quickly and is effective over many different stains, including water, tannin, smoke, rust, pencil, ink, nicotine, and coffee. Block Out primes, seals, protects, and can be used on bare or previously painted surfaces; interior drywall, plaster, wood, or masonry; and exterior masonry surfaces. Can be used as a spot primer for exterior wood shingles/composition siding.