With the nearly total phase-out of oil-based paint, the question of whether you can paint over oil-based paint with latex is as important as it is rare. If a house is old enough, it's inevitable that it will have oil-based paint at least somewhere. But houses like this are becoming rarer as more homeowners paint over oil-based paint surfaces.
- Latex paint can be applied over oil-based paint. There is nothing inherent in the oiled-based paint material that precludes an additional latex layer.
- The surface must be properly prepared. Glossy surfaces will not take a second layer of paint well.
- Preparation includes deep clean, sanding, and dry cleaning with a tack cloth.
- Use a primer before putting down the latex. While advisable for most painting projects, it is a requirement for this one.
- Oil-based paint cannot be applied over latex paint.
- If you have multiple layers (five or more) of oil-based paint, consider scraping off the paint first.
- When you can do this on exteriors, interior use is more forgiving than exterior use.
Where's the Oil?
Key surfaces such as door casing, window trim, baseboards, and kitchen cabinets were commonly coated with oil-based (alkyd) paint. Since these are high-impact surfaces subject to wear and degradation, there will come a time when you need to paint them again.
There is a very good reason for using oil-based paint. It levels flat, leaving zero brush marks, gaps, bubbles, or holes. Door casing or a window sills painted in white oil-based paint is a beauty to behold, a museum piece: glass-smooth and rock-hard.
As a side note, oil-based paint isn't entirely banned; technically you can still purchase it in smaller, one-quart quantities. But when you go to the paint store or home improvement store, you find that oil-based paint is difficult to purchase. For many stores, it isn't worth it to carry a one-quart product-only product that many homeowners balk at using.
One reason: volatile organic content (or VOC). When it dries, oil-based paint emits a host of VOCs that are harmful to the environment. On an individual level, homeowners mostly don't like oil-based paint's difficult clean up procedures (a spirit must be used, not water).
How To Prepare the Surface for Your Latex-Over-Oil Project
1. Scuff the Surface to Remove Gloss
With fine grit sandpaper, scuff down the surface of the oil paint layer for improved stickability.
This has less to do with the initial coat being oil-based than the fact that this is a paint-over-paint project. Even when using similar types of paint, you will never get as good adhesion as you would by laying down paint upon primed wood.
Aim for eliminating surface sheen, or gloss. Gloss is as much an enemy of paint adhesion as is dirt.
2. Damp Clean to Remove Dirt, Mold, Mildew
Untold layers of dust and dirt may compromise the paint's ability to stick. While you can sometimes "cheat" on cleaning latex-over-latex projects, this project is different and requires deep cleaning.
You will need to build drying time into the project. Use a damp cloth (not wet) to clean the surface after you do the sanding. Add TSP (trisodium phosphate) to the water to improve cleanability. TSP is a cheap white, non-toxic powder available in most hardware and home improvement stores.
3. Dry Clean to Remove Last Specks of Dust
Use tack cloth to lightly wipe down the surface. Tack cloth is an inexpensive, simple product made of cheesecloth impregnated with beeswax. Its sticky surface is perfect for vacuuming up those last stray motes of dust. Do not rub too hard. Applying hard pressure will result in leaving wax on the surface--difficult to remove.