How to Prep Oil-Based Paint for Latex Paint

Many older homes, and some upscale new homes, have been painted with oil-based (alkyd) paint--particularly on trim and cabinets. Proper prep is critical when you're repainting over the oil-based paint with latex. Failing to properly prepare the surface, and either not priming or using the wrong type of primer, almost guarantees you catastrophic paint failure because latex paint will not adhere to oil-based paint. It's not a difficult process; follow the steps and have a paint that will stick for life.

Difficulty: Moderate

Instructions

Things You'll Need:

• Rubbing alcohol
• Rags
• Power sander
• Sanding pole
• Sandpaper or sanding sponge
• Liquid de-glosser
• Mineral spirits
• Oil-based primer
• Roller
• Roller cover
• Brush
• Paint tray or 5-gallon bucket and grid

1. Test the existing paint if you're not sure whether it's water- or oil-based. Clean a small section, then rub it with rubbing alcohol. Oil-based paint is impervious to rubbing alcohol but latex will start to rub off and will get a little sticky.

2. Clean the surface with mild detergent and water if it's very grimy, otherwise the grime will clog up your sandpaper. Let it dry.

3. Repair cracks, dents and gaps with the appropriate filler: joint compound, spackle, wood filler or paintable silicone caulking.

4. Sand the entire surface until it is dull. Use a flexible sanding sponge for intricate areas on trim. Use 80-grit sandpaper and a power sander to make fast work of flat areas. A drywaller's pole sander will make it easy to sand walls and ceilings.

5. Clean the sanding dust off with mineral spirits or liquid de-glosser.

6. Prime with an oil- or shellac-based primer. Use either type of primer on interior surfaces; only use an exterior oil-based primer on exteriors. Use an oil primer formulated to resist rust for exterior metal surfaces. The primer can be brushed, rolled or sprayed.

7. Paint at least one coat of latex (two on exterior surfaces) after the primer is dry.

Tips & Warnings

• It's OK to paint latex over oil-based primers; they are very flat and porous and designed to be painted with either oil- or water-based paint.
• Don't sand oil-based paint applied before 1980. It probably contains lead, and sanding it will release lead dust into the surroundings. Either use liquid de-glosser before priming, or take appropriate cautions for working with lead paint. (See Resources.)

References

• House-Painting-Info: Can you paint latex over oil base on walls?
• "Seattle Post-Intelligencer;" A Simple Test for Oil-Based Paint; James and Morris Carrey; October 2006

Resources

• Environmental Protection Agency: Lead Information
• Painting With Acrylic Water Based Paint On Top Of Oil Based Alkyd Paint