How to Prepare Wood Trim for a Smooth Paint Job

Here's how to wash, sand, scrap and fill woodwork for a smooth finish.

Do you want your old trim to look fresh, smooth and crisp after you've painted it? These tips show you how the pros do it. They're DIY friendly, so you can prep your trim yourself and still get professional-looking results.

By the DIY experts of The Family Handyman Magazine

TIME

One day

COMPLEXITY

Simple

COST

$20 - $100

A good paint job starts with good prep work

The old adage,“ A good paint job is 90 percent prep work and 10 percent painting, ” is absolutely 100 percent true. A quick coat of paint applied over existing paint or stain may look good—but it won't last.

The key to a long-lasting paint job is to prepare the woodwork so it's clean and gloss free. In this story, we'll show you how to achieve a mar-free surface that'll hold paint for 10 years or even longer. Best of all, the new paint job will look like you hired it done by a nitpicky pro. Whether you're repainting painted wood or painting wood that's been stained and varnished, the steps and tips we show here apply to any woodwork—door, window or trim.

Real pro painters know they can't rush a job. This story will show you key tips on how the pros remove a surface layer of paint to prepare interior woodwork for optimum adhesion of the new primer and paint. We don't show you how to strip layers of old paint down to bare wood using heat or chemical strippers.

CAUTION

If your home was built before 1979, check the paint for lead. Call your public health department for instructions on how to do it. Don't use the scraping or sanding techniques we show here on lead paint because doing so will release lead dust, the primary cause of lead poisoning. For more information on lead.

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Wash the woodwork

Have two buckets and two scrub sponges at hand (such as Scotch-Brite scrub sponges), one each for washing solution and clear water rinsing. Don't wash with a cloth rag, as it may shine a flat surface or dull a lustrous one. The goal is to remove the grime so you don't push it farther into the wood during sanding.

Use a non-soapy detergent (such as Dirtex, Spic & Span or TSP No-Rinse Substitute according to label directions. Regular TSP (tri-sodium phosphate) also works, but it leaves a white film that requires a lot of rinsing, and it can irritate your skin.

It's not available in some states. Dip a scrub sponge into the cleaning solution and wring it out enough to keep it from dripping. Wash wood from the bottom upward with slow, easy up-and-down strokes so the solution has time to soften the grime .If you start at the top, the cleaner can run down the wood and create hard-to-remove streaks.

Only clean one section at a time so the wood won't dry before you rinse off the cleaner (if directions call for rinsing). To rinse, dip the rinse sponge in clear water and wring it drip free, then wipe the surface clean in one pass. When you begin to wash a new area, start well within the clean area to avoid streaking.

Change both the cleaning solution and the rinse water often—whenever the water becomes cloudy. Spend twice as much time cleaning the wood in areas of high hand contact such as windows, door frames and around light switches and handles/knobs, and places that attract high airborne particles (all wood in kitchens, bathrooms and laundry rooms).

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Remove stains with special cleaners

If stains from markers, ink or the like resist initial cleaning, remove them with a specialty cleaner such as Goof Off. Otherwise, they'll bleed through the new paint. If all else fails, apply a stain-hiding primer such as Zinsser's B-I-N to cover it.

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Hand-sand all woodwork to remove all surface shine

Hand-sand all woodwork smooth with a fine, 180-grit paper until all shine disappears (right). A coarser-grit paper will remove more than necessary (use 80- to 120-grit to smooth imperfections such as heavy globs of old paint).

If the outside paint layer is gummy, use a “clog-resistant,” or “self-lubricating,” sandpaper (such as 3M's SandBlaster paper). It has an anti-load coating that keeps the paper from clogging.

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Buy a sanding block and sanding sponges

The right tool improves the sanding job:

  • A folded sheet and finger pressure work great for most areas.
  • A rubber sanding block is comfortable to grip, works well with feathering and lets you apply more even pressure in stubborn areas like windowsills.
  • A sanding sponge or pad conforms readily to curves and crevices.

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Test the paint adhesion

Perhaps you've moved into a house where the previous owners threw on a quick coat of paint—and now you're stuck redoing it (haven't we all been there!). To determine if the new paint will hold, scribe an “X” lightly into the surface paint layer with a razor blade. Firmly stick duct tape over the mark and yank it away quickly. If any paint adheres to the tape, it's unsound and should be removed.

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Scrape loose paint

Use a 2-in. carbide-blade scraper (the Maxx Grip Tungsten Talon by Hyde Tools is one) to eliminate areas of hardened grime, flaking or chipped paint, and thick paint globs.

Buy one that fits your hand and features a replaceable carbide blade. Pull the scraper in the direction of the wood grain, and use finesse and elbow grease to “rake” the paint away but not gouge the wood. Scrape until the remaining paint won't budge and you have nice, crisp (but not sharp) edges in the details of the wood.

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Dust and vacuum thoroughly

When the first sanding and scraping step is complete, dust off all areas with an old paintbrush and vacuum woodwork with a brush attachment.

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Clean out crevices with a putty knife

For small, tight areas, scrape with a 1-1/2-in. flexible putty knife. Use a pushing motion to go under the paint—working from an area of loose paint to an area where paint is firmly adhered. This bevels the remaining paint layers to make a smooth transition between damaged and undamaged areas, and it renews the details in the wood.

Consider Liquid Sandpaper, Especially on Lead Paint

After final sanding and vacuuming, some pros go the extra step of wiping woodwork down with a liquid sandpaper/deglosser (such as Wil-Bond by Wilson-Imperial or ESP by Flood). This step will ensure a good bond. And if you have to deal with lead paint, this step can replace sanding.

Wipe down woodwork with a paint deglosser or
liquid sandpaper.
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Check for flaws with a trouble light

Position a hand-held bulb (at least 60 watts) so it shines across (rakes) the wood surface to detect loose paint, rough edges and other blemishes in the surface to determine what needs to be filled. Take a pencil and lightly circle spots that need work.

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Fills holes with lightweight spackling compound

Cracks, depressions and other surface defects before painting. Holes filled with a heavy coat or several layers of paint may look good initially, but the result won't last. When the paint dries, these filled areas will often reopen. Fill all chips, holes and cracks with spackling compound. Use a lightweight compound that dries fast and doesn't shrink. If you use a type that shrinks, fill anything 1/16 in. or deeper twice.

Apply more filler than is needed to each hole with a flexible putty knife, then smooth it by pressing down and pulling toward you. Then use the widest putty knife you have to feather out the filler—and keep sanding to a minimum.

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Rebuild damaged corners with a two-part filler

For damaged corners, use a two-part wood filler (like Minwax's High Performance wood filler) or an automotive body filler like Bondo. Both are tough, won't shrink and stick like glue.

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Caulk between woodwork and walls

Apply a thin bead of paintable acrylic latex caulk only inside the crack where wood meets a wall for a smooth, professional appearance. Remove extra caulk with a putty knife. And buy a dripless caulk gun to save time and frustration. Cut the tip smaller than you think you need.

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Feather out filled areas with fine-grit sandpaper

Use 320-grit sandpaper over all filled areas to flatten and feather them out. Dust off the sanded areas with an old paint brush, and vacuum with a brush attachment.

Finish by wiping down the wood with a damp cloth if using water-based paint or a tack cloth if using oil-based paint. Spot-prime filled areas, especially if you're using gloss or semi-gloss paint, or else the paint will be dull in filled areas.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Caulk gun
  • Bucket
  • Drywall sander
  • Dust mask
  • Paint scraper
  • Putty knife
  • Shop vacuum
  • Paintbrush

You'll also need a trouble light.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • Sandpaper (course, medium and fine grit)
  • Sanding sponge
  • Rubber gloves
  • Sanding block
  • Spackling compound
  • Detergent
  • Cleaning sponges
  • Liquid sandpaper
  • Two-part wood filler
  • Duct tape
  • Acrylic latex caulk