Richard's HOLZTITE Alkyd Enamel Undercoat Primer/Sealer is our finest professional alkyd primer/sealer, specially formulated for application to a variety of both interior and exterior substrates. Easy to apply, it provides excellent coverage, penetrates and seals new substrates, provides excellent enamel holdout, excellent adhesion, and is mildew resistant. It resists bleeding of tannic acids, which are present in most new wood species, has excellent sanding properties, may be applied to previously painted surfaces, and is mildew resistant and meets MPI Standard #136 of the Master Painters Institute's approved products list. Great for both interior & exterior use.