Stain Blocker is General Finishes' revolutionary water-based stain-blocking primer for interior projects. Stain Blocker can be used to protect pigmented finishes from stain, dye and wood tannin bleed-through. Brush or spray over an existing finish, raw wood or MDF as a base coat for light-colored General Finishes Milk Paint and Pigmented Polys. See our spray tip size recommendations here. General Finishes Stain Blocker is designed for effectiveness, not price point. This primer has a sophisticated resin system and an atypical formulation. Use on pieces where you are concerned about bleed-through.