Professional painters tend to go with paints that make their work stand out. Quality of finish rather than odor or clean up conveniences guide their selection process.
Most homeowners and do-it-yourself-ers, on the other hand, like to use latex paints for the many user-friendly advantages of latex. This preference works out fine except when it comes to enameling, which is where they can run into problems.
All is fine and well until it comes time to paint the woodwork, for example, in a new house that a painter originally enameled with oil-based paint when the house was first built.
The painter may have used his favorite oil enamel because it leveled out so well and made his work look good, leaving the homeowner in a difficult situation, when the time comes to re-paint. So, how does one go about painting latex paint over oil based enamel?
Give the cleaner some "dwell" time to penetrate into any grime before wiping it off. If it has been awhile since the last painting, clean it twice, and/or use a scouring pad in conjunction with the cleaner. Don’t scour if you are unsure about the age of the paint on the surface or if the trim is old (“old” as in pre-1978, since it’s important not to disturb lead-based paint).
Dull
(Note: do not sand or scour a pre-1978 painted surface as it may contain lead. See EPA lead page before proceeding.
I highly recommend dulling the previous enamel before painting it. The only exception to this rule is when one is attempting to paint over lead based paint. (In this case, simply clean the surface thoroughly and use one of the recommended primers listed below.)
Sanding resurfaces the substrate and provides a fresh, clean, anchor for the primer. You are always better off if you sand. You can accomplish both cleaning and dulling in one step by using the scour pad during cleaning. (You can do this in lieu of sanding.)
One of the nice qualities of oil-based enamel is that it sands easily. Latex paints are gummy and sticky and will gum up the sand paper when you sand them. Oil-based paints do not gum up the paper, making a light pre-paint sanding possible. It’s better to prepare surfaces that are covered with latex paint during cleaning instead, by using the scour pad along with the pre-paint cleaner.
Use fine sanding paper (220 grit) or sanding sponges. You want to de-gloss and level out any old brush marks, knocking any debris off of the old paint. Once sanded, remove the sanding dust with a shop vac and follow that up with a wipe-down using a micro fiber tack rag. Don’t use a regular tack rag before applying a latex paint since the oil in the tack rag will repel latex paint.
Dry
I will skip any lengthy dissertation on this other than to say the surface needs to be dry, thus allow the pre-paint cleaner to dry, etc.
Priming
This is the most critical step when converting over from oil to latex. You must prime. Use either an oil primer or shellac-based primer.
There are some latex primers that may work, but you may get a crackle finish with some of them. I don’t take the chance. Oil and shellac primers have been used for years for converting oil to latex, so I stick with the sure thing.
Recommended Bonding Primers
- Xim 400 white (oil)
- Zinsser’s Coverstain (oil)
- B-I-N (shellac)
Use good ventilation with these primers during and after priming, as each have a strong odor.
Once the woodwork is primed, you have successfully converted your surface over to latex and may paint with latex enamel.
Clean - Dull - Dry
Let’s start with the universal rule for re-painting: clean, dull and dry. It’s possible to paint over any painted surface that fits this description. Let’s look at these three points before we begin thinking about applying any finish paint.
Clean
First and foremost, if you want your paint to stick, the surface you are painting must be clean. Dirty and contaminated surfaces will repel coatings applied over them. A good cleaner for re-painting woodwork is Krud Kutter‘s "Prepaint Cleaner." Spray it on and wipe it off. (No need to rinse.)
Please read lead paint warning if your house was built before 1978,
Painting and Decorating Concourse Home > Interior Painting Tips > Painting Latex over Oil Based Paint
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How to Paint Latex Over Oil Enamel
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