Which surfaces require primer and why?

• A. Topcoat alone provides adequate adhesion on all surfaces.
• B. Porous or stained surfaces, new wood, metal, and repaired areas to improve adhesion and seal porosity.
• C. Only concrete surfaces require primer.
• D. Primer is unnecessary when the topcoat is water-based.

Answer: (B)

Surfaces vary in porosity, staining, and how well paint will cling, so using a primer helps the finish coat bond reliably and look even. Porous or stained surfaces, new wood, metal, and repaired areas need primer to seal the pores, block stains or tannins, and create a uniform adhesion plane for the topcoat. Primer on porous materials prevents rapid absorption that can cause uneven color and lap marks, and it also blocks resin or tannin bleed from knotty wood. Bare metal benefits from a primer to prevent corrosion and to provide a good bonding layer for paint, especially if the metal surface isn’t already prepared. Repaired or filled areas require primer to seal the patches so the topcoat applies smoothly and highlights are minimized.

Topcoat alone isn’t reliable on all surfaces, and primer isn’t reserved only for concrete. Surfaces with visible stains, new wood, metal, or patched areas all benefit from primer, and water-based topcoats don’t automatically eliminate the need for a primer in these cases.