Expert Advice: Paint Prep

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When doors aren't properly prepped before repainting, chips and dings are inevitable.

When doors aren't properly prepped before repainting, chips and dings are inevitable.

Paint is peeling off my interior doors where they meet the jamb. Why is this happening, and how can I stop it?

Q

Duffy Hoffman: Unfortunately, this is a sign of corners being cut during the paint job. A lot of people don’t understand that proper prep is critical on previously painted surfaces. Without it, new paint won’t adhere properly and will eventually begin to peel.

Q

Doors are one of the biggest challenges. Because they take a lot of abuse, they’re often the first place you’ll notice bad paint prep. When doors in houses from the 1830s to the 1950s were first coated, they were most likely primed with a lead-based oil primer, followed by two coats of lead-based oil paint. These hefty original coatings need to be sanded off in order for any new coats to properly adhere.

To check whether your paint has good adhesion, do a crosshatch test on one of the doors. (If one door has adhesion problems, they usually all do.) You’ll need a roll of masking tape and a sharp knife. Take the knife and make a tic-tac-toe design on the door, slicing down to the first coats of paint. Next, apply the tape over this mark. Leave it on for a day before yanking it off in a quick motion. If paint coatings come off with the tape, it means proper preparation was not done.

Painting over poorly adhered coatings will not cure the problem; the result will be that the new paint will start chipping after it’s bumped or the door is closed hard. Until the paint coatings are completely removed, the challenge of chipping paint will continue.

To paint a door with well-adhered previous coatings, first check the door for fit. (A poor fit can add to the problem, rubbing on the jamb and causing friction.) Using proper dust protection, sand all surfaces of the door with 100-grit sandpaper, including the edges, top and bottom—you can leave the door hanging for this. Vacuum all dust off the door, and wipe it down with a cloth dunked in warm water and a dab of dish soap to clean grease and get dust out of profiles, which is critical to good paint adhesion. Next, take a tack rag and lightly wipe the door down, unfolding the rag as you go so you’re always using a clean part to dust off door surfaces.

Once the door is completely dry, it’s time to prime it. Use a quality oil brush and the oil primer of your choice. Always mix penetrol (paint additive) into the primer for a smoother finish. If you want it to dry faster, add a little Japan drier (an accelerator) to your pot, and mix well. (If painting a color, tint the primer to match.) Apply a thin coat of primer to the door, and let it dry to manufacturer’s specifications—don’t rush it, as doing so invites paint failure.

Once the door is properly primed, you can use an oil or latex paint to finish it. Before applying the first finish coat, scuff the door down with 150-grit sandpaper, then clean it as you did above before applying a thin coat of finish paint.

When using oil paint, place 2" of paint from the can into a separate container, then add 2" of penetrol and mix thoroughly. (When finishing with latex, mix the paint with flowtrol.) This formula, if done correctly, will give you a great, clean sheen and an even finish. Always apply two coats, sanding and cleaning between them. After it dries, wipe the finish coat off with a wet rag only (no soap).

For doors where paint is not well-adhered after a crosshatch test, your only option is to take down the door, remove all of the previous coatings, and start over. You may be able to dry scrape if paint removes readily when a scraper is pulled across the door. If not, use an infrared heater (a safe and fast way to remove paint). After removing all the paint, sand the door with a palm sander until it’s smooth, then follow the same process as above to get a long-lasting, great-looking paint job.