How To Cover Nail Holes in Trim

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His name was Callachan.  The “ch” distinguished it from the Irish version, and he was proud of his Scottish heritage.  He was the fastest trim carpenter within a hundred miles.

“Custom Cal, the Contractor’s Pal” was his business slogan, and he charged $10 an opening – windows, doors, sliders, the opening didn’t matter.  He could trim out a one-floor house in a day.  He was a whiz, and he never ran out of work in the construction business.  This was in the ‘70s and ‘80s.

Today, we do our best to live up to the standard he set working on our own house.  We use a finish nailer for its speed and convenience, and the finish nails leave little nail holes you sometimes have to search for to find.  

But they’re there, and they need to be filled before the wood trim gets painted. We want the wooden surface to be completely smooth and with a professional touch.  After all, it’s our own home, and we take pride in our work.  

What to fill them with and how to fill those nail holes are the questions for today.

What Are The Two Main Types of Wood Filler?

Wood Filler

The door and window trim, the crown molding, and the baseboard have been installed, and the installation went well.  Everything is square, corners mitered, the nail holes small from the finish nailer (sometimes we use a power brad nailer) barely showing.  But we know they are there, so our attention then turns to filling them so we can add a couple of coats of paint.

Our choices at the hardware store or one of the large DIY stores include both a water-based wood filler and a solvent-based wood filler.

Water-Based Wood Fillers

 Just as the name implies, this type of wood filler is water-based.  It’s creamy in texture and is easy to smear in and on the wood.  It’s also easy to smooth with your finger and to clean both off your finger and off the wood.  Just keep a damp cloth handy for both purposes.  It does not require much force to push into the hole because of its consistency, and your finger will do just fine.

The advantages of a water-based wood filler are its drying time – around 15 – 20 minutes, easy cleanup, and the ability to sand it smooth with fine-grit sandpaper.  It takes paint well, and if smoothed properly, a primer and cover coats will hide the nail holes completely.

A product like Aqua Coat Water-Based Wood Putty dries quickly and is sandable when dry, as well as stainable and paintable.  It’s a beige putty as is, although it can be colored to custom match the wood/stain you intend to use.  If the trim will be painted, be sure to use a primer first, maybe even a product like Kilz.

Solvent-Based Wood Fillers

These fillers are oily in texture and will get sticky during use.  You’ll find them difficult to clean up after if you wait until they dry.  Whereas water or a damp cloth cleans water-based wood fillers easily, you’ll need something a bit stronger to clean a solvent-based wood filler – a nail varnish remover works well on a clean tack cloth, or some other solvent will do this for you.  

A solvent-based wood filler may well include vinyl or epoxy, as well as a higher VOC content, and as a consequence, will have an odor to them.  VOCs (volatile organic compounds) are emitted as gas at room temperature and are present in many products we use to build our homes.  They can irritate your eyes, nose, and throat, so you do not want to breathe them.  When using a product with a high VOC content, a respirator or mask is recommended.  

It takes longer to dry than a water-based wood filler and more work to clean up after when you’re done.  But, a solvent-based wood filler product like DAP will harden well and look and act like real wood – sandable to smooth, can be cut, drilled, and planed when necessary, and is much stronger than the water-cased cousin. It, too, takes paint and stain well. 

Is a Water-Based Wood Filler Sufficient?

Since the project is inside the house, where the climate is fairly evenly controlled, the wood filler you choose doesn’t have to be that strong.  In that sense, a water-based wood filler will be sufficient.

We’re going to cover the trim, and thus the nail holes, with a good primer and a couple of coats of paint.  These will provide additional stability to the water-based wood filler, too.   So, since the filled nail holes will be covered and stabilized by the primer and paint, a water-based wood filler is certainly sufficient for interior use.  

If the trim is going to be painted, the color of the wood filler won’t matter.  However, you can customize the color of the filler to match the wood or stain you are using, and kits are even available for this purpose.

Do You Need To Fill The Nail Holes In Your Interior Trim?

Of course, you do.  Custom Cal was a finish carpenter.  He installed the trim expertly and well.  You’ve taken the time to do the same in your own home.  You want to finish the job with that same degree of professionalism and take pride in your work. 

If you take the easy way out and decide to simply cover the nail holes with primer and paint, yes, it will look good at first.  But as the paint dries, little dimples will form, and the holes become even more prominent.  If you are staining the trim or using a clear seal, it becomes even more important to fill those nail holes.  You’ll also want to match the color of the filler with the stain, so the nail holes simply blend in with their surroundings.

Don’t cheap it out.  Go the extra step and fill the nail holes.

Filling Nail Holes in Interior Trim

The process is an easy project, and the tools required are few.  Gather your water-based wood filler, a putty knife, a clean, damp cloth, and fine-grit sandpaper, 180 or 220 grit.  

Fill The Nail Hole With Your Finger

The nail hole is so small no tool is really needed.  Use your index finger to press the filler into the hole and give it a swipe; then repeat this to overflowing.  Overfilling the hole is recommended just to be sure; you’ll sand it after it dries, so you don’t need to have it flush with the wood surface at this point.

Fill The Nail Hole With a Putty Knife

If the hole is larger or deeper, you might need or want to use a putty knife.  They are like a spatula but made for this particular purpose.  If you used screws to install the trim, the hole will be larger, and the knife will make the job of filling it easier.  Or you might have dinged the trim with your hammer, and there is a dent needing to be filled and smoothed flush with the wood surface.  Push the filler into the hole or ding, and use the blade to wipe away the excess filler.

Use Your Finger as Sandpaper

Using a water-based wood filler allows finger play.  Wipe off excess filler with your fingers, or use a clean glove for the purpose.  It works well, and if you miss anything, that fine-grit sandpaper can take care of the rest.

Let It Dry and Then Sand

Give the filler 20 minutes to dry unless the hole or ding you filled was larger than a finish nail hole.  That fine-grit sandpaper will bring it home to a smoothness that is ready to paint or stain.  

Clean It and Paint/Stain

This is where the clean cloth or the tack cloth comes in handy.  Remove any dust particles from the wood surface, and the trim is ready for whatever finish you have chosen.

Other Nail Hole Filler Options

Guardsman Wood Repair Filler Sticks - 5 Colors Plus Sharpener, Repair and Restore Scratched Furniture

We do prefer to work with a water-based wood filler for all of the reasons we’ve enumerated – easy to apply, easy to clean up, quick to dry, suitable for interior trim work, can be painted over or stained, and the holes disappear.  

However, there are other options beyond a water-based and a solvent-based wood filler.  

  • Glue and sawdust.  We’ve written about making your own wood filler in a past piece, which you will find here.  A little wood glue and sawdust from the wood with the nail hole being filled can be mixed together right on the wood surface and pressed into the hole.  This method will take stains and paints well.
  • Stainable fillers.  If you have decided to stain the trim, there are fillers that are made specifically to take that stain.  They will be marked as “Stainable,” and there are some good products to choose from on the market.
  • Crayons.  Yes, crayons, although not Crayola.  There are wood finish crayons that come in a variety of colors to match the stain you’ve chosen, and rubbing them over the nail hole with some pressure will force the material into the hole.

We turn to our most reliable source for backup on these additional options – The Old House.  It’s only 4 minutes long, but it contains a wealth of information to supplement what we have provided here.

Notwithstanding these other options, we still like the “hands-on” approach to filling our nail holes in the trim we’ve installed around the new windows and door.  Getting a little dirty, but cleaning up easily, makes the project a little more real and enjoyable for us.

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