I just installed a new exterior door. I put the original, painted interior-side casing back on, but to make it line up properly I put some new, unpainted 1/4" trim strips (not sure what they're called exactly) between the door frame and the casing.

I need to repaint it all, but how do I prepare it? There are seams between the strips that I'd like to hide, and some small (less than 1/4") gaps in places between the casing and the door frame.

Do I caulk the gaps? Spackle them? What about the seams where two pieces meet?

2 Answers 2


The strips you made and installed are called extension jambs. We use them all the time to fit new windows and doors. I usually sand and prime them before I install them, but if you have already installed the jambs and old trim, here are a couple of ways to finish them off.

  1. Put a straight piece of blue painters tape down the wall adjacent to the door trims.
  2. Sand the edges carefully so the jambs and trim are flush.
  3. Clean off the dust and apply a bead of latex/acrylic painter's caulk.
  4. Using a 1" putty knife, smooth the caulk to a nice flat layer against the jamb/trim.
  5. Remove the tape immediately. Retouch the caulk gently if removing the tape leaves a ridge.
  6. Let the caulk cure for 24 hours. Minor imperfections can be smoothed out with a sharp utility knife and a damp cloth. If there is some shrinkage in the larger gaps, add a little more caulk, smooth off with your putty knife, let cure.
  7. Paint.

There are painter's caulk that will "fast dry" in an hour, that you may consider. If you are unhappy with the final leveling of the caulk, you can also use a super thin layer of lightweight spackle (not standard vinyl spackle) applied with a putty knife over the caulk. This product dries in about 20 mins and can be lightly sanded or shaped with a damp cloth.

  • nice edit. like the numbered list. guess that is why I pound nails for a living instead of write blogs! Feb 4, 2011 at 6:14
  • ha, and maybe why I write software instead of pounding nails... Feb 5, 2011 at 17:47

Without seeing the gaps it's difficult to give definitive advice, but caulk or paintable frame sealant would be my filler of choice for this sort of job.

It will work with both the gap between the trim and the frame and the gaps between the strips.

After applying a bead of filler smooth it down with a damp cloth or (which I find easier) a damp finger. This pushes the filler further into the gap as well as making it level with the surface.

Allow to dry and paint as normal.

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