How to Fill Nail Holes in Trim

Using a filling knife to fill a hole in plank of wood
Steve Gorton / Getty Images
Overview
  • Working Time: 5 mins
  • Total Time: 20 mins
  • Yield: Per 8 linear feet
  • Skill Level: Beginner
  • Estimated Cost: $5 to $20

Installing door or window trim, baseboards, or crown molding always results in nail holes in trim that need filling. These might be pencil-lead-size holes caused by finish nails or tiny pinprick holes caused by power brad or finish nailers. For a clean appearance, you can quickly fill in these holes before painting. This is a simple project involving only a few tools, yet the results will help your project look truly professional.

Choosing a Wood Filler

There is a major difference between water-based and solvent-based wood fillers. Water-based fillers, such as Elmer's Carpenter's Wood Filler Max are creamy to smooth on and easy to clean up, but they are weak when spread out over wide areas. Solvent-based fillers are sticky and oily and difficult to clean up if you wait until they dry. The advantage of solvent-based fillers is that they dry rock-hard, far stronger than their crumbly water-based counterparts. With interior nail holes, however, you don't need the filler to be very strong at all. Also, in many cases the filled holes will be covered with primer or paint, both of which provide some stability for water-based fillers.

For wood trim that will be painted, you can use any color of wood filler, since it will be covered with paint. If the trim is pre-finished or you will finish it with stain and/or clear sealer, carefully select a color-matched filler that blends with the natural coloring of the wood. Fillers come in a few different colors to match common wood species. You can also purchase kits that include a filler base and colorants that you mix together to create custom colors.

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Watch Now: How to Fill Nail Holes in Trim

What You'll Need

Equipment / Tools

  • Putty knife

Materials

  • Water-based wood filler
  • 180- or 220-grit sandpaper

Instructions

  1. Apply the Filler With Your Finger

    For most nail holes, the space to fill is so small that it is best to use your finger. Put a small dab of filler onto your index finger. Press the filler into the hole, and give it a quick smear. Repeat, if necessary, to fill the hole completely. It's best to overfill the hole slightly, leaving a slight, smooth ridge over the area.

  2. Apply Filler With a Putty Knife (optional)

    Deeper or larger holes may require the assistance of a putty knife. The putty knife allows you to scoop up wood filler from the container and to firmly press it into the hole while keeping your fingers clean. The main value, though, is that you can use the putty knife to scrape across the trim to remove excess wet putty. This minimizes the amount of sanding your have to do later on.

    To use a putty knife, take up a small amount of filler from the container, about the size of a dime. Transfer the filler to the trim. Force the filler into the hole. In the same motion, scrape the putty knife down the trim to remove the excess. Deposit the excess putty back into the container.

    Close the lid on the wood filler between applications, as filler hardens quickly. Even a minute or two is enough for the filler to begin to develop a dry shell on top.

  3. Sand With Your Finger

    One benefit of using crumbly water-based filler is that your finger can act as a type of sandpaper. After the filler has dried for about 15 minutes, sand off the crumbles and protrusions with your finger. A clean cotton glove works well as a sanding device, too.

  4. Finish With Sandpaper

    If you do a good enough job sanding with your finger, sanding down the filler with real sandpaper is almost unnecessary. But sandpaper will always give you a bit better finish. Using, 180- or 220-grit (extra-fine) sandpaper, gently sand the filler with only a few passes. Harder or more numerous swipes will only wear down your trim board. 

  5. Remove the Sanding Dust

    Clean the surface with a tack cloth. Do not rub hard with the tack cloth hard or you risk embedding the surface with wax. Once the surface is dust-free, it's ready to prime, paint, stain, or sealer.

Is Filling Holes Necessary?

If you used an electric brad nailer to install the trim and it was perfectly calibrated, you should have nail holes that are nearly invisible. In this case, it is your choice whether you want to fill them. From a distance, these holes will recede. This means that crown molding is a good candidate for unfilled nail holes. Arguably, crown molding is a distant type of trim since it is attached at the ceiling level and minor details are not visible.

Often, though, shallow depressions are left when you are done, especially if you manually hammered in finish nails with a hammer and recessed them with a simple metal punch-like device called a nail set. Even those tiny holes produced by a power nailer may show up when the light hits the surface at a low angle.

If you are installing trim in more than one room and have other projects to attend to, not filling the holes in the trim may save some time. A medium-sized room with trim, such as one with crown molding, baseboards, two windows, and one door, may take about one hour to complete. Many homeowners and even some professionals paint right over the holes because the paint will somewhat fill in small holes. But if you want a smooth, hole-free trim surface, you can obtain that level of perfection with little work by filling in the holes before painting.