Some 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 degradation, there will come a time when you need to paint them again.
There was 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.
But when you go to the paint store or home improvement store, you find that oil-based paint is difficult to purchase.
The reason: volatile organic content (or VOC). When it dries, oil-based paint emits a host of VOCs that are harmful to the environment. Due to regulations that began to go into effect in the 2000s, most states have limited oil-based paint to quart-sized only sales.
- Latex paint can be applied over oil-based paint.
- The surface must be properly prepared, though.
- Preparation includes deep clean, sanding, and dry cleaning with a tack cloth.
- Use a primer before putting down the latex.
- Oil-based paint cannot be applied over latex paint.
- If you have multiple layers (five or more) of oil-based paint, you cannot apply latex paint over it.
- When you can do this on exteriors, interior use is more forgiving than exterior use.
How To Prepare the Surface
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.