How to Fill Nail Holes in Trim

Using a filling knife to fill a hole in plank of wood
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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 truly professional appearance, you will want to fill in these holes before painting. What should you use: caulk, wood putty, wood filler? And how should you go about doing this?

Should You Fill Nail Holes or Not?

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, they will recede. This means that crown molding is a good candidate for unfilled nail holes. Arguably, it is a "distant" type of trim, since it is attached at ceiling level and not very visible.

Often, though, shallow depressions are left when you are done, especially if you manually pounded 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 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 pros 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.


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Use Water-Based Wood Filler Not Wood Putty

There is a huge 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 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/paint or stain/sealer, both of which provides some stability those water-based fillers.

Wear Vinyl or Nitrile Gloves

Are you in the habit of using latex, vinyl, or nitrile gloves when painting with latex paint? Perhaps not. This water-based paint is so easy to clean up, wearing gloves is practically useless.

But it is good practice to have gloves on hand for oil-based paints and stains and or for dealing with very dirty places like sewer or sink traps or toilet installation.

Using wood filler is another instance when they come in handy. You would certainly want them if you were dealing with solvent-based filler: easier to strip off those gloves than to be washing concrete-hard crud off your hands for the next week. They are useful, too, even for water-based fillers.

Use Your Finger

Should you use a putty knife? It would make sense to dip in a putty knife and use it to fill the nail holes. Not really.

For nail holes, the space to fill is so small that it's 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's preferable to have a slight, smooth ridge over the area.

Use Your Finger as Sandpaper

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 Real 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.