Perfect Trim (how to fill nail holes)

What's that you don't see? Nail holes! I went nuts trying to get perfectly smooth trim when we replaced all of it in our house mini-remodel. It seems so simple, so easy to putty and paint, but those darn nail holes are really hard to hide completely (really, look around at your and your friends' houses). In my mission to hide the holes, I scoured contractors' blogs, which have tons of passionate posts on various methods.

I figure I filled about 800 nail holes, caulked 850ft, and painted about 600ft of trim over 3 weeks--that's a ton of prepping holes, cutting perfect paint lines to the wall, not painting our newly finished floor, and painting door jams and window sills.

New trim before and after new trim

The Headache

The problem with common trim is that it's typically made out of MDF (medium-density fiberboard), so any bit of water will make it balloon out like pressed wood. You can't simply slap on pink putty and paint. My painstaking method took 3 days to complete a section of trim.

Step-by-Step Process

  • Spray or brush paint the 16ft boards. They're already pre-primed but a good coat now will make it easier on the baseboards since you won't need to cut perfectly to the floor. How to fill nail holes: spray paint

  • Cut the baseboard or trim piece to length How to fill nail holes: cut trim

  • Nail gun the baseboard or trim to the wall

  • Caulk the seams. From here on out, use a headlamp all the time--really helps see small imperfections. I found it best to caulk a length of board and getting an ample amount of caulk on there. Then quickly come through with a damp finger to smooth. You'll waste like 2x the caulk. How to fill nail holes: caulk

  • Sand the nail holes since they mushroom out a bit with the nail gun. I used 220grit sandpaper on a sanding block. How to fill nail holes: sand putty holes

  • Vacuum dust out of nail holes and wipe down with damp cloth. If you leave the dust from your sanding in the holes, it'll expand when you putty the hole and you're back to mushroom.

  • Put lightweight putty in nail holes and let dry overnight. Don't use the heavier pink putty--that works better in drywall. The lightweight putty will mushroom less. How to fill nail holes: putty How to fill nail holes: putty

  • Sand putty holes How to fill nail holes: sand nail holes

  • Repeat putting a coat of lightweight putty on the holes again--often the putty will collapse in and won't be perfectly flat. Let it dry (less time than overnight) and sand again.

  • Lightly wipe away dust with damp cloth.

  • Run your fingers over the trim with your eyes closed. If you can feel anything, you'll be able to see it when you're done. Re-putty if needed.

Here's what a ready-to-paint hole typically looks like. The edges of the mushroomed nail hole are sanded off, the putty is perfect with the wall, and your pre-painted board is pretty sanded.

How to fill nail holes: ready to paint hole

  • Put oil based paint over the puttied areas and exposed ends of MDF to seal it. Let dry. The oil seals the exposed pressed fiberboard, else the latex paint will mushroom it again. How to fill nail holes: oil base primer

  • From here, use your favorite method to get a perfectly straight wall-trim paint line. I did it with tape and a double-cut method since painter's tape doesn't block paint perfectly, especially on textured walls.

Ex: If your wall is red and trim white, paint over your trim like 1/2" where they meet the wall with red. Let it thoroughly dry overnight and put painter's tape on the wall at the seam. Paint the edge of the tape with the wall color to seal the tape (shown below on the lower right of the picture before the white's painted).

Paint the trim with 2 coats of white, being careful not to paint your newly refinished hardwood floor! Peel off the tape while the 2nd coat is still wet. I found it best to peel off the tape at a very sharp angle.

How to fill nail holes: paint technique

It was a ton of tedious work but the crisp lines were worth it!

If you're in the San Jose area, FMD Distributors (floor, moulding, doors) is a great place for material at contractors' prices, a fraction of the cost of Home Depot or Lowe's.
How to fill nail holes: finished product