There are four basic ways to fix a gap in trim molding. You have the choice of filling in the gap with a shim, applying a self-hardening filler such as carpenter’s putty, removing and reinstalling the trim, or replacing it with newly cut pieces.
1. Using a Shim
If you don’t want to go through the trouble of reinstalling or replacing the trim molding and the gap is wide enough, consider cutting a small wedge of wood and using it as a shim. With a little precision, it may fit perfectly in the gap. This works especially well if the trim is painted, for the repair work is easily hidden.
2. Using a Filler
If the gap is small enough, you might be able to get away with simply filling it in with putty or another filler and painting over it. This method is not advisable, though, if the trim has a natural finish.
3. Reinstallation or Replacement
The two other options are reinstalling the existing trim or replacing it. Remove the trim gently and attempt to reinstall it so the angled cuts match perfectly. If this does not work, your only choice may be replacement. Take special care to make accurate cuts to ensure the pieces fit flush and are the correct length.
A gap in trim molding can be unsightly. One of these four methods can, however, resolve the issue relatively easily.