How can I tell if my trim has oil-based paint on it?

Dampen a cotton pad with rubbing alcohol and rub a hidden spot on the trim for half a minute or so. If paint comes off on the pad or the surface goes soft and tacky, it is water-based. If nothing happens, it is very likely oil-based. Old oil paint is also often yellowed, hard and glassy.

Why did my new trim paint peel off in strips?

Almost always because water-based paint was put directly over oil-based or glossy paint without the surface being dulled and primed. The new coat dries on top rather than gripping in, and any knock, tape or scratch lifts it away. The fix is to strip the loose coat, sand, prime with a bonding primer and repaint.

Can trim be painted with oil-based paint again?

California's limits on solvents in paint have pushed most trim enamels toward waterborne formulas, and traditional oil-based options are harder to find. Modern waterborne alkyd and urethane enamels from Dunn-Edwards and Sherwin-Williams level out and harden much like the old oils did, without the yellowing, and they are the usual choice over properly primed old trim.

Is a deglosser enough instead of sanding?

A liquid deglosser helps clean and dull the surface, and it is useful on detailed profiles that are hard to sand. It is not a replacement for a scuff-sand and a bonding primer on trim that takes regular knocks, such as baseboards and door frames. Most good jobs use cleaning, sanding and priming together.

Painting Over Oil-Based or Glossy Trim

Water-based paint will not grip old oil-based or high-gloss trim on its own; it sits on top and peels or scratches off in sheets. The trim has to be tested, degreased, scuff-sanded to a dull surface and coated with a bonding primer made for glossy surfaces before the new enamel goes on. In a pre-1978 home, test for lead before sanding.

Older San Diego homes very often have the same problem hiding on their baseboards, door frames and window casings: decades of oil-based enamel, hard and glossy, with a yellow cast in the rooms that get little sun. It looks like a surface that is ready for paint. It is not. A coat of ordinary water-based paint rolled or brushed straight onto it will look fine for a week and then come off in strips the first time a vacuum cleaner bumps the baseboard or a strip of tape is pulled off.

It is one of the most common failures on interior trim, and one of the most avoidable.

Why new paint will not stick to old gloss

Paint grips a surface in two ways: chemically, by bonding to what is beneath it, and mechanically, by keying into a slightly rough surface. Cured oil-based enamel is hard and non-porous, and gloss is smooth. Water-based paint applied over it can do neither. It dries as a skin lying on top of the old finish, held there by little more than contact. That is why it can sometimes be peeled away from a corner in one long piece.

Heavy glossy latex enamel, common in kitchens and bathrooms, behaves in much the same way, and so does trim that has been waxed or polished over the years.

First, find out what is on your trim

The rubbing alcohol test works on most trim:

Pick a hidden spot, such as the back edge of a door casing or inside a closet.
Wipe it clean, then rub it with a cotton pad dampened with rubbing alcohol for about half a minute.
If color comes off on the pad or the paint turns soft, it is water-based.
If nothing changes, it is most likely oil-based.

Other clues: oil paint tends to be very hard, glassy and yellowed, especially on the trim of north-facing rooms and inside closets where daylight never reaches it.

If the home was built before 1978

Many homes from that era in National City, La Mesa and the older neighborhoods of San Diego have trim that was first painted when lead paint was still sold. The bottom layers of that trim may contain lead. Sanding is the step that turns intact old paint into dust, so the trim should be tested before any sanding begins. Ebenezer is EPA lead-safe (RRP) certified, so if the test finds lead, the sanding is contained and cleaned up the way those rules require.

The preparation, in order

Clean and degrease. Trim collects years of hand oil, cooking film and cleaning products. A degreasing cleaner, then a clean water rinse, comes before anything else, because sanding a greasy surface only spreads the grease into the scratches.
Repair. Dents, gouges and split miters are filled now, along with nail holes. Loose or failed caulk is cut out.
Scuff-sand. The goal is not to remove the old paint but to take the shine off every part of it, so the surface is uniformly dull. Profiled trim is sanded with flexible sanding pads that follow the shape.
Remove the dust completely. Vacuum, then wipe with a tack cloth or a damp cloth. Sanding dust left in a corner is a weak layer of its own.
Prime with a bonding primer. A primer formulated to adhere to glossy and hard surfaces is the bridge between the old oil and the new waterborne enamel. Both Dunn-Edwards and Sherwin-Williams make primers for exactly this.
Caulk. Joints between trim and wall are caulked after priming, which gives the caulk a better surface.
Two finish coats of enamel, with the time between them that the label calls for.

Which finish paint goes on top?

California’s limits on solvents (VOCs) in paint, enforced in this county by the San Diego air district, have made traditional oil-based enamels harder to find, and in most cases they are no longer the best choice anyway. Waterborne alkyd and urethane-modified enamels, such as Sherwin-Williams Emerald Urethane Trim Enamel, flow out to a smooth, hard finish that resembles oil, without its long drying times, strong smell or yellowing. In a semi-gloss or satin sheen, they are the usual answer for trim.

Patience while it cures

Enamel feels dry within hours, but it keeps hardening for days to weeks, depending on the product, the temperature and the humidity. Near the coast, on damp marine-layer mornings, that takes longer. During that time the finish is softer than it looks. Doors can stick to their stops, furniture pushed back against a baseboard can leave a mark, and tape should not go anywhere near it. A little care in the first weeks is what lets the finish reach its full hardness.

Why the estimate takes trim seriously

On many homes, the trim can take more hours than the walls. There is more edge for the area, more detail, more preparation, and every step above has to happen on every piece. An estimate that treats old oil trim as one more coat has missed what is on it. The trim should be tested when the home is looked at, and the plan built around what is found, not around what it looks like from the doorway.

If your trim is yellowed, chipped or peeling from an earlier repaint that did not hold, it can be made right. Read more about interior painting, see how a job runs, or ask for a free estimate and have it looked at properly.