Preparing Wood Trim for Painting

painted wood trim molding

If you need to paint wood trim molding around walls and ceilings, taking time to prepare the surface properly will reward you with a beautiful, durable finish for years to come. Whether your trim is bare wood, or it has been painted before, you will need to be sure the surface is smooth and all holes and gaps are filled, before the finish enamel is applied. This page contains steps and techniques for preparing bare, and previously painted interior wood trim molding for painting.

Choosing Your Materials

There are only a few items required to prep wood trim for painting:

  1. a putty knife to scrape peeling paint and apply fillers
  2. a paint scraper for rough oil-based paint
  3. sandpaper or a sanding sponge to smooth out rough spots and spackled patches
  4. acrylic latex caulk and a caulk gun to fill gaps
  5. painter's putty to fill small nail holes
  6. spackle or wood putty to fill large holes and gouges
  7. oil-based under coat primer

Scrape and Sand

peeling paint on wood

Previously painted trim may require scraping to remove loose, peeling paint. This is often the case with old, oil-based paint when it pops off in random spots, leaving rough edges between sound areas and bare spots. Use a flexible putty knife on these spots to force off all the loose paint that will come free. Work pushing out from the center in all directions to encourage paint with a weak bond to come off. Sand these spots with 80 grit sandpaper, followed by 120 grit, to blend a smooth transition with the sound paint that remains. Remove the sanding dust with a vacuum cleaner or tack cloth and "spot prime" these areas with oil-based under coater.

If you have newer painted trim that is in good condition, it will only require a light sanding to be ready for the finish paint. Use 220 grit sandpaper or a sanding sponge to gently scuff it up a bit giving the surface "tooth" to aid in bonding with the new paint coat.

Prime Bare Wood

If you have bare wood trim, you will need to prime it with a good quality oil-based under coater to give the finish paint a solid foundation. This will insure your trim looks its best, and stays that way for a long time to come.

First, be sure you're starting with a smooth surface by going over all the wood with 120 sandpaper or sanding sponge to give it a light sanding. Most new wood trim will be smooth to start with, but there may be some rough spots that need attention like scarf joints, or at corners where two pieces of wood trim meet.

Vacuum or wipe the sanding dust away with a tack cloth and apply the primer. Let the under coat dry at least overnight before proceeding with the finish coat. Don't wait longer than the label recommends before applying the finish paint so the primer is fresh and at its best.

caulking a baseboard

Fill Holes and Gaps

When the primer is dry, make any repairs to gouges and large holes using wood putty or trim spackle, and fill small nail hole with painter's putty. Use acrylic latex caulk to fill gaps where wallboard meets molding, and seams where molding pieces come together. Use plenty of caulk to completely fill the gaps and wipe off all the excess before it sets up.

stripping paint with heatgun

Stripping Old Paint

When it comes to old, oil-based paint on woodwork there will often be patches where some of the old paint has come off and the rest is still intact, leaving a patchwork of paint chips. If you want to restore a finish like this to a consistently smooth surface, you will need to remove the areas where the original coating still remains, bringing everything down to the same level. The best way to achieve this is with a paint heat gun.

Stripping this old paint, which most likely contains lead, present a problem with lead fumes released into the air. This may be prohibited in some areas by state or local regulations. It can also be a health hazard for the person using the heat gun to melt the old paint. If you choose to use this method to strip paint, the heat gun you use must not exceed 700 degrees Fahrenheit, according to EPA rules, to keep fumes out of the air. Even at this temperature it's a good idea to wear an appropriate respirator to avoid breathing the fumes while using the heat gun.