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.