Gaps in crown molding
easy 1–2 h
Tools: caulk gun, utility knife, damp rag, ladder, brad nailer or hammer and nail set · Materials: paintable elastomeric acrylic caulk, brad nails, touch-up paint
Steps
- Photograph the widest gap against a ruler in winter and again in summer; a gap that opens in winter and closes in summer is seasonal movement, and the fix is flexible caulk, not more nails.
- Cut out the old cracked caulk with a utility knife and wipe the joint clean and dry.
- Run a bead of elastomeric caulk along the gap, tool it with a damp finger, and paint once cured; it will stretch with the seasons instead of cracking.
- For a section that has pulled away from the wall, push it back and nail through the moulding into the wall stud or the ceiling joist, not just the drywall.
- At corners, caulk the joint or, if a piece has shrunk, glue and pin a thin filler strip painted to match.
- If a gap opens along the ceiling in winter everywhere in the room, it may be truss uplift — nail the moulding to the wall only and let it float against the ceiling.
Stop and call a pro if
- gaps wider than 6 mm (¼ inch) that keep growing, or cracks spreading into the drywall — the structure is moving
- the moulding is plaster or the ceiling is lath and plaster with loose sections
- the room has a cathedral ceiling or the moulding is more than 4 m (13 feet) up
What a pro does that you can't
A finish carpenter re-cuts and re-fits moulding that has shrunk or shifted, adds backing where there is nothing to nail to, and a builder checks for truss uplift when the gaps appear every winter.
DIY cost: $10–25 in caulk and nails