How to Prepare Trim for Painting

Trim, baseboards, and moldings add architectural interest to any room, and a fresh coat of paint makes these features stand out even more. Our tutorial shows you several tips for properly preparing your trim for paint.

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Door and window trim, as well as baseboards, cornices, moldings, and chair rails, make a major design contribution to the style of a room. Whether finished with paint or stain, trim must be properly prepared. This normally means setting nailheads below the surface of the wood, filling and sanding holes, cleaning, and repairing or replacing damaged wood. It can also require the removal of old paint or varnish to provide a fresh surface for the finish.

Whether you finish your trim before or after painting the walls, it's best to have all the preparation work completed on both the trim and the walls before finishing either surface.

Be sure to wear protective glasses when stripping and a dust mask when sanding. Chemical strippers can contain toxic fumes, so ventilate the room adequately before applying the stripping solution. Rubber gloves are also a must to keep the chemicals from burning your hands.

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Before You Begin: Test for Lead

Lead is a hazardous material used as an ingredient in paints before the late 1970s. In 1978 legislation banned its use, but your house could still contain lead paint. There are prescribed precautionary steps you should employ in the removal of lead paint, but in some cases you'll need to call a professional to stabilize or remove these materials.

The best ways to abate lead-paint hazards in your house include:

Paint removal: Scrape paint from peeling walls and woodwork with a broad knife. Wear a respirator as you work. You can apply chemical paint strippers to soften the paint. If you dry-scrape the paint, mist the surface with a spray bottle to reduce hazardous dust. Clean up dust and particles with a wet mop—vacuuming it spreads lead dust. Sanding, sandblasting, and similar methods aren't recommended because of the dust hazard. And softening paint with a heat gun could create toxic fumes.

Encapsulation: Instead of removing the paint, isolate it or seal it off. Apply new drywall over an existing wall or float the wall with wallboard compound.

Surface replacement: Remove and replace woodwork and moldings that have been painted with lead paint.

How to Remove Gloss from Trim

Step 1: Scuff-Sand Surface

New paint or clear finish will not adhere well to gloss paints. Scuff-sand all glossy surfaces with 150-grit sandpaper. Use a sanding block or palm sander on flat surfaces or a contour sander on curved surfaces.

Step 2: Remove Particles

After scuff sanding, the surface will contain microscopic dust particles left in the grooves by the sandpaper. Pull these particles off the surface with a soft cloth dampened in mineral spirits or water. Don't use a tack cloth; it can leave a residue that will interfere with the paint bond.

How to Fill Nail Holes

Step 1: Push Nailheads

Use the right size nail set to push nailheads below the surface of the wood. Set the point of the nail set in the recess of the nail head and tap sharply with a hammer.

Step 2: Fill Nail Holes

If you will ultimately paint the surface, slightly overfill the nail holes with interior wood filler. Sand it smooth when dry.

Step 3: Add Putty

For clear finishes, buy different colors of putty and use the one that most closely matches the finished tone of the wood.

Bonus: Smooth Putty with a Spatula

The usual putty-application procedure involves rubbing your finger over the hole. But if you've installed several rooms full of trim, you can easily rub your fingertip raw before completing the job. Also your finger can dip into the hole, creating a slight depression. Use an ordinary kitchen spatula as a solution. It's firm enough to wipe away excess putty and leave a smooth surface. It also conforms to curved surfaces, speeding your work.

How to Patch Trim for Painting

Step 1: Wash Surface

Wash the surface of the trim with a TSP solution or a low-phosphate household cleaner. Rinse thoroughly with a vinegar/water solution and let the trim dry. Use a stiff putty knife to scrape loose paint to the bare wood.

Step 2: Apply Wood Patch

Apply high-quality latex wood patch in nail holes, dents, and other damaged areas. Overfill the area slightly to accommodate its tendency to shrink. Let the filler dry.

Step 3: Sand Smooth

Sand the repaired area smooth with 150-grit sandpaper. If the filler has shrunk below the surface of the wood, reapply another layer, and sand it after it's dry.

How to Prepare Stained and Varnished Trim

Step 1: Clean and Sand Surface

Clean varnished surfaces with a soft cloth and odorless mineral spirits. Scuff-sand the entire surface with 150-grit sandpaper.

Step 2: Apply Wood Patch

Apply stainable wood patch whose color matches the surface closely. Level the patch and sand it smooth when dry.

Step 3: Restain Patch

Restain the patched area to match the finished surface. Apply the finish coat.

How to Remove Paint with Chemical Strippers

Step 1: Apply Stripper

Apply a thick coat of stripper to the surface with an old natural-bristle paintbrush (many strippers will melt nylon bristles). Brush in only one direction to avoid lifting the stripper off the surface. Let the stripper work for about 20 minutes, then remove it and the paint with a scraper.

Step 2: Repeat Process

Reapply stripper where paint is still adhered and repeat the process. Remove small flecks of paint with a coarse abrasive pad, cleaning it with water or mineral spirits, depending on the stripper you've used. Finally, clean the surface with a fine abrasive pad dipped in denatured alcohol.

How to Use a Heat Gun to Remove Paint

Pull the trigger of the gun and let it come to its working temperature. Hold the gun with its tip at an angle and just close enough that it softens the paint without burning it (and the wood underneath). When the paint bubbles, back the gun away from the surface slightly and scrape the paint.

How to Sand a Flat Surface

For large or small flat surfaces, a palm sander or random orbit sander is a great timesaver when sanding walls or woodwork.

How to Sand a Contoured Surface

Contoured surfaces are difficult to sand with rectangular sanding blocks because they can gouge the wood. Use flexible sanding blocks or sanding sponges to smooth these curved surfaces.

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