How to Fill Nail Holes in Trim

Using a filling knife to fill a hole in plank of wood
Steve Gorton / Getty Images

Installing door or window trim, baseboards, or crown molding always results in nail holes in trim that need filling. These might be large divots caused by finish nails or barely perceptible pinprick-sized holes caused by power brad or finish nailers.

For a clean appearance, you will want to 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.

How Do You Fill Nail Holes?

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 more than one room of trim and have other projects to attend to, not filling the holes in the trim may save some time. A medium-sized room of 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.

Wood filler is weaker than trim materials such as wood, PVC, or MDF. This means that, during sanding, the wood filler will sand down before its surrounding material will. Priming and painting over the wood filler subsequently strengthen the wood filler.

Project Metrics

  • Working Time: 15 minutes per 8 linear feet
  • Total Time: 15 minutes
  • Skill Level: Beginner
  • Material Cost: $5 to $20

What You Will Need

Tools/Materials

  • Latex or nitrile gloves
  • Water-based wood filler
  • Sandpaper
  • Putty knife
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Watch Now: How to Fill Nail Holes in Trim

Instructions

Begin With Water-Based 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 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 good part of solvent-based fillers is that they dry rock-hard, far stronger than their crumbly water-based counterparts.

With interior nail holes, you don't need the filler to be very strong at all. Also, the filled holes will be covered with primer or paint, both of which provide some stability for those water-based fillers.

Use Your Finger as a Tool

Use latex, vinyl, or nitrile gloves when applying wood filler. For most holes, the space to fill is so small that it is better to use your finger. Put a dab about the size of a quarter of a pea on your favored index finger. Press it in and give it a quick smear. One smear should be enough, two at the most.

In the end, only the hole itself should be filled. But at this point, it is often preferable to have a slight, smooth ridge over the area.

Use the Putty Knife as a Tool

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 saves on sanding later on.

To use, 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 back in the container.

Tip

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

Sand With Your Finger

One benefit of using that crumbly water-based filler is that your finger can act as a type of sandpaper.

After the filler has dried for about 15 minutes, you must sand off the crumbles and protrusions with your finger. A clean cotton glove works well as a sanding device, too. Latex, vinyl, and nitrile tend to tear, though, of the three, nitrile will last the longest.

Finish With Sandpaper

If you do a good enough job in previous steps, sanding down the filler with real sandpaper is almost unnecessary. But sandpaper will always give you a bit better finish.

With #180 to #100 (fine) sandpaper, lightly swipe each filled nail hole one or two times. Harder or more numerous swipes will only wear down your trim board. 

Clean the surface with a tack cloth. Do not rub the tack cloth in hard or you risk embedding the surface with wax. After that, the material is ready to prime, paint, stain, or seal.