Replace interior door casing
Fit new mitered trim around an existing sound doorway.
Home · 3–5 hr · Medium
Before you start
Resolve old-paint lead hazards before cutting or prying. Wear eye protection; clamp trim for cutting and keep hands out of the saw path. Do not place fasteners where hidden pipes or wiring may be present.
Tools and materials
- Matching casing, finish nails, wood glue, filler, paintable caulk, primer and paint
- Utility knife, pry bar, protective block, combination square, tape, miter box and hand saw, hammer and nail set
Check the problem
Check that the jamb is sound
Casing covers the joint; it does not fix a loose frame or a binding door. Correct those problems first.
Match profile and coverage
Measure casing width and thickness, wall gaps and adjoining baseboard. Choose trim wide enough to cover old edges without obstructing hinges.
Steps
Remove the old casing
Score caulk and paint seams after hazard checks. Pry in small stages against a wide protective block, then remove exposed nails.
Clean and mark the reveal
Remove ridges and loose caulk. Use a combination square to mark a consistent reveal on the jamb, commonly about 3/16 inch unless the existing detail differs.
Cut and dry-fit the head
Measure between reveal lines. Cut opposing miters on the head piece, leaving it slightly long for a test fit. Trim gradually until it meets both lines.
Fit the two legs
Measure each leg separately from floor to the short point of its top miter. Cut and test with the head; do not assume both sides are identical.
Fasten without twisting
Glue the mating miters and hold the reveal. Pilot near ends if needed. Nail the inner edge to the jamb and outer edge to sound framing with suitable lengths, avoiding the door’s operating clearance.
Fill, finish and inspect
Set heads below the surface, fill holes, caulk the wall edge and finish after drying. Check tight joints, secure trim and free door movement.
Set heads below the surface, fill holes, caulk the wall edge and finish after drying. Check tight joints, secure trim and free door movement.
Tips
Tune the actual corner
Walls and jambs may not be exactly square; dry-fit instead of trusting one saw setting.
Avoid end splits
Predrill close to ends and do not overdrive.
Use it at the wall edge
Do not use a thick caulk bead to hide a badly fitted miter.