How to Prepare Wood Trim for a Smooth Paint Job

Updated: Dec. 21, 2023

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

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Do you want your old trim to look fresh, smooth and crisp after its painted? 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.

Tools Required

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

Materials Required

  • Acrylic caulk
  • Cleaning sponges
  • Detergent
  • Duct tape
  • Liquid sandpaper
  • Rubber gloves
  • Sanding block
  • Sanding sponge
  • Sandpaper
  • Spackling compound
  • Two-part wood filler

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 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. We’ll show you how to achieve a mar-free surface that’ll hold paint for 10 years or longer. Whether you’re repainting wood or painting wood that’s been stained and varnished, the steps here apply to doors, windows or trim painting.

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.

Project step-by-step (13)

Step 1

Wash the Woodwork

  • You’ll need buckets, sponges and detergent;
    • Pro Tip: 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.

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Step 2

Wash the Trim

  • Clean and rinse one section before moving onto the next section;
  • Wash wood from the bottom upward with slow, easy up-and-down strokes so the solution has time to soften the grime.
    • Pro Tip: If you start at the top, the cleaner can run down the wood and create hard-to-remove streaks.
  • Change both the cleaning solution and the rinse water often — whenever the water becomes cloudy.
    • Pro Tip: Spend extra time cleaning areas that have a lot of hand contact, like around door handles 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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Step 3

Use Special Cleaners to Remove Stains

  • Use a heavy-duty cleaner on stains, or cover them with a stain-blocking primer.
  • If stains from markers, ink or crayons resist initial cleaning, remove them with a specialty cleaner. Otherwise, they’ll bleed through the new paint. If all else fails, apply a stain-hiding primer.

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Step 4

Sand All Surfaces to Remove the Shine

  • Hand-sand all woodwork smooth with fine, 180-grit sandpaper until all shine disappears.
    • Note: 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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Step 5

Test Paint Adhesion

  • Pull duct tape off the paint to see if the paint sticks;
  • 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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Step 6

Scrape Loose Paint

  • Use a 2-in. carbide-blade scraper to eliminate areas of hardened grime, flaking or chipped paint, and thick paint globs;
    • Note: 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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Step 7

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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Step 8

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 has firmly adhered.
    • Pro Tip: This bevels the remaining paint layers to make a smooth transition between damaged and undamaged areas, and it renews the details in the wood.

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Step 9

Check for Flaws With a Trouble Light

  • Position a hand-held work light so it shines across the wood surface to detect loose paint, rough edges and other blemishes in the surface to determine what needs to be filled;
  • Use a pencil and lightly circle spots that need work.

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Step 10

Fill Holes With Compound

  • Use a flexible putty knife to fill all chips, holes and cracks with spackling compound.
    • Note: 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.
  • Use a lightweight compound that dries fast and doesn’t shrink.
    • Pro Tip: Apply more filler than is needed to each hole with a 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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Step 11

Rebuild Damaged Corners

  • For damaged corners, use a two-part wood filler or an automotive body filler like Bondo. Both are tough, won’t shrink and stick like glue.

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Step 12

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.
    • Pro Tip: Buy a dripless caulk gun to save time and frustration. Cut the tip smaller than you think you need.

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Step 13

Feather out Filled Areas With Fine-Grit Sandpaper

  • Prime areas that are filled with a compound;
    • Pro Tip: If you don’t do this, the dull spot will show through the finished coat of paint.
  • Use 320-grit sandpaper over all filled areas to flatten and feather them out.
  • Dust off the sanded areas with an old paintbrush, 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.

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