Oil-based paint once ruled the world of interior paint for high-impact areas such as trim work, doors, and cabinets. When it dries, oil-based paint emits a host of VOCs (volatile organic content) that are harmful to the environment. The paint is often messy and smelly since mineral spirits or paint thinner must be used for clean up, not water.
If a house is old enough, it is inevitable that it will have oil-based paint somewhere since water-based latex paint wasn't introduced until the 1940s. And newer houses might have some areas of oil-based paint since it is not entirely banned: Oil-based paint is still available in quart sizes or smaller. Many professional painters even favor oil over latex for a smoother, rock-hard finish that leaves no brush marks, gaps, or bubbles. You'll typically find oil-based paint used on door casings, trims and moldings, mantels, cabinetry, and shelving.
Can You Paint Over Oil-Based Paint?
Latex paint (and even other oil-based paint) can be successfully applied over older oil-based paint as long as the surface is fully cured and there is nothing inherent in the coating that prevents another layer of paint to be added. Preparation is important. Glossy surfaces will not take a second layer of paint well, so they need proper cleaning and priming achievable by following these steps. Before you begin painting, make sure to get enough paint to finish the project with the help of The Spruce's Paint Calculator.
Equipment / Tools
- High-quality paintbrush
- Fine 180-grit to 220-grit sandpaper
- Medium 100-grit to 150-grit sandpaper (optional)
- Putty knife or five-in-one tool
- Tack cloth
- Wood putty or wood filler
- TSP (trisodium phosphate)
- Paint primer
- Soft sponge (for TSP)
- Protective glasses
- Protective gloves
De-Gloss the Surface
With sandpaper, manually scuff down the surface of the oil-based paint layer for improved stickability. Aim for eliminating surface sheen or gloss; the goal isn't to remove all the paint, just scuff up the surface so new primer and paint can adhere well. If fine-grit sandpaper isn't working well, switch to gentle scuffing with medium-grit sandpaper.
If you are scuffing up cabinetry or trim with details, you may prefer to sand by hand instead of using a power sander which may offer too much pressure on the surfaces.
Pry off any loose paint from the walls with a five-in-one tool or putty knife.
Fill small gaps and holes with wood putty or wood filler. Let filler dry completely. After holes are dry, lightly sand gaps with fine-grit sandpaper.
Dry Clean With Tack Cloth
After the surface is completely dry, gently use a tack cloth to lightly wipe down the surface to catch any more dust, dirt, or sandpaper granules.
Tack cloth is an inexpensive, simple product made of cheesecloth impregnated with beeswax. Its sticky surface takes up stray dust particles. Use gently; applying hard pressure will result in a waxy surface which can be hard to remove.
Deep Clean the Surface
If the surface is exceptionally dirty and greasy even after using a tack cloth, your best bet is to use TSP to do a deep cleaning before priming.
Mix 1/4 cup to 1/2 cup (for extra dirty surfaces) TSP with a gallon of hot water. Use a sponge that's damp with the TSP solution to wash the surfaces. Wash surfaces from bottom up to reduce streaking.
After cleaning with TSP, sponge the surface with fresh water to rinse (there are no-rinse TSP formulas). Let the surface thoroughly air-dry.
TSP, known as trisodium phosphate, is a harsh but effective cleaning chemical used to prepare walls and other surfaces for paint. It also acts as a de-glosser. When using it make sure you have adequate ventilation, skin, and eye protection.
With the surface completely dry and clean of dirt, you can now prime the surface to prevent the peeling of latex paint over oil paint.
After the primer is dry, you're ready to paint. Let the paint dry for at least two hours. Paint the surface a second time.
For the best painting technique, do not load up the brush with too much paint; only dip the tip of the bristles into the paint. Draw the paint in slow, even strokes, always maintaining a wet edge.