What preparation is needed for painting over a gloss oil-based finish on my interior doors in Vancouver?

Painting over gloss oil-based finish requires thorough surface preparation to ensure proper adhesion — the key is either sanding to create tooth for the new paint to grip, or using a specialized bonding primer designed for glossy surfaces.

The challenge with gloss oil-based finishes is that they create an extremely smooth, non-porous surface that new paint simply cannot grip. Without proper preparation, your new paint will peel, chip, or scratch off easily, especially on high-touch surfaces like doors. This is one of the most common paint failure scenarios in Metro Vancouver homes, particularly in character houses and older properties where oil-based trim paint was standard.

Surface preparation has two main approaches. The traditional method involves light sanding with 220-grit sandpaper to "scuff" the glossy surface, creating microscopic scratches that give the new paint something to grip. Sand just enough to dull the shine — you're not trying to remove the old paint, just roughen it. After sanding, clean thoroughly with TSP (trisodium phosphate) or a degreasing cleaner to remove all dust and residue. This method works well but is labour-intensive, especially on paneled doors with detailed profiles.

The modern approach uses a bonding primer specifically designed to adhere to glossy surfaces without sanding. Products like Benjamin Moore Fresh Start Multi-Surface Primer, Sherwin-Williams Extreme Bond Primer, or Zinsser Bulls Eye 1-2-3 are formulated to chemically bond to slick surfaces. These primers cost $40–$65 per gallon in Metro Vancouver but can save hours of sanding time. Clean the surface thoroughly with degreaser, apply the bonding primer, then topcoat with your chosen paint.

For interior doors in Metro Vancouver's humid climate, proper preparation is even more critical because doors expand and contract with seasonal humidity changes, putting stress on the paint film. A poorly adhered topcoat will crack and peel at the stress points. Use a high-quality acrylic-alkyd hybrid paint like Benjamin Moore Advance or Sherwin-Williams Emerald Urethane Trim Enamel for the topcoat — these provide the hardness and durability of oil paint with the flexibility and low odour of latex.

Practical steps for your project: Remove the door and hardware if possible for easier access and better results. Clean with TSP or degreaser, then either sand lightly with 220-grit and tack cloth, or apply bonding primer directly to the clean surface. Prime any bare wood areas with a quality primer. Apply your topcoat in thin, even coats — two thin coats perform better than one thick coat. Allow full cure time between coats (typically 6–12 hours for acrylic-alkyd hybrids in Vancouver's humidity).

When to hire a professional: Door painting requires patience and technique to avoid brush marks, drips, and uneven coverage. If you have multiple doors or detailed panel doors, a professional with spray equipment can achieve a factory-smooth finish that's difficult to match with brush application. Professional door refinishing typically costs $150–$300 per door including removal, prep, priming, and two topcoats.