Fix a gap in a trim corner
A gap in a trim corner, where two pieces of baseboard or door casing meet at a miter, opens when the wood shrinks or the nails let go. Small seasonal gaps in painted trim just need caulk. Bigger ones can be glued and pulled closed with a couple of finish nails driven across the joint, which keeps them from opening again. Caulk hides a gap; glue and nails close it.
How trim corners are joined
Trim corners are joined with miters: each piece is cut at an angle so they meet in a clean line. Wood shrinks across its width in dry weather and swells in humid weather, so a miter that was tight when it was installed can open in winter, usually wider at the inside (short point) of the joint.
Corners also open when the nails holding each piece miss the framing, when the wall or floor settles, or when the joint was never glued. A gap that opens and closes with the seasons is wood movement; one that keeps growing means something has come loose.
Why trim corners open
Dry seasons open miters.
A piece pulls away.
The joint had nothing holding it.
Walls and floors move a little.
| You see | What it means | Start at |
|---|---|---|
| Hairline gap in winter | Seasonal movement | Step 6 |
| Gap growing over months | Joint came loose | Step 2 |
| One piece sticking out | Loose piece | Step 2 |
| Stained trim with a gap | Needs color fill | Step 6 |
Let's fix it
- Check if it's seasonalNote the time of year. A thin gap that shows up in winter and closes in summer is normal wood movement, and caulk or filler is the right fix. A gap that keeps getting wider or has one piece sticking out needs gluing and nailing.
- Clean out the gapScrape out old caulk, dust and loose paint with a utility knife so glue can reach bare wood. Check that both pieces are tight to the wall; if one is loose along its length, nail it to the framing first as in the loose door trim guide.
- Glue the jointWork wood glue into the open miter with a thin putty knife or a toothpick, getting it onto both faces of the joint.
- Close and cross-nail itPress the two pieces together. Predrill a small hole through the edge of one piece and across the joint into the other, then drive a 1 to 1 1/4 inch finish nail or brad, shorter for thin trim. Do the same from the other side, a little higher or lower, so the nails cross. Wipe off squeezed-out glue right away with a damp rag.
- Set and fill the nailsSink the nail heads just below the surface with a nail set. Fill the holes with wood filler, let it dry and sand it smooth.
- Caulk or color-fill and touch upOn painted trim, run a thin bead of painter's caulk into any hairline gap left, smooth it, and paint. On stained trim, use a colored wood filler or wax filler stick that matches, then buff it. Touch up the finish.
Watch it done
- The corner is closed and flush
- Nail holes are filled
- The finish matches
Opened again? Check that both pieces are nailed into framing.
If the whole piece is loose
If the whole piece of door trim is loose, see the guide for fixing loose door trim.
If baseboard is pulling off the wall, see the guide for reattaching a baseboard.
What a pro typically charges (a rough estimate; prices vary by area): A handyman or finish carpenter typically charges $75–$200 to close and touch up a few trim corners.
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Trim corner gap questions
How do I fix a gap in a trim corner?
Glue the miter, press it closed and drive finish nails across the joint from both sides, then set, fill and touch up.
Why do trim corners separate?
Wood shrinks in dry weather, and corners that weren't glued or are nailed into drywall only open up.
Can I just caulk a gap in trim?
On painted trim, yes, for small seasonal gaps. Larger or growing gaps should be glued and nailed first.
How do I fill a gap in stained trim?
Use a colored wood filler or wax filler stick that matches the stain, then buff it.
Should I glue trim miters?
Yes. Glued miters stay closed far better than nailed ones.