Crown molding requires special attention to fix gaps at corners.
Several factors cause gaps in crown molding. The first is poor craftsmanship. Incorrect installation leaves uneven corners and space behind or above the molding. A home also shifts over time. In old houses, it's possible for the walls and ceiling to change shape sufficiently that they pull away from the molding in places. The final common culprit is seasonal change. Changes in humidity can have drastic effects on wood construction. All of these problems can be addressed with guidance and attention to detail.
Instructions
Shifting Structures
1. Examine the molding thoroughly. Note any gaps that are present. Pay close attention to potential causes. Check for uneven corner joints and consistent gaps between molding sections. Look for locations where the molding does not make contact with the wall or ceiling.
2. Insert shims into gaps along the walls or ceiling. Drive the shims into the gap as far as possible without putting outward pressure on the molding. Break off any exposed ends. Tack the gaping section in place with a finish nail.
3. Cover the gap with drywall mud. Use a knife to push the mud into the gap. Smooth the mud away from the molding so that the wall appears to be a single continuous plane. Do not allow the mud to clump at sections you have filled.
Poor Installation
4. Sand away minor inconsistencies between molding angles. Add wood putty to any minor cracks or blemishes.
5. Remove pieces of molding that were cut short, or smaller pieces that were used to cover an extended section of wall. Measure the unfinished length of wall. Note any angled cuts required to fit a new piece.
6. Do not assume that the corners of the room are exactly 45 degrees. Use a bevel gauge to check the angle instead. Loosen the bolt on the joint of the bevel gauge. Set the gauge into the inside corner --- or around an outside corner. Tighten the bolt while holding the two ends of the gauge tight to the wall.
7. Take the bevel gauge to the miter saw and set the handle against the back rail. Adjust the angle of the saw so that the slot on the saw base matches the slot on the bevel gauge. Look at the reading on the saw base. Divide this number by two. This is the angle of your first cut.
Pick a piece of molding more than long enough to fill the space you've uncovered. Cut the angle you measured at one end.
8. Measure the molding to the length of the wall and mark the location for the second cut. Find the angle of the second corner and set the saw to the new angle. Cut the second angle at the far end of the molding from the first. Cut the piece a little long and try to fit it into the space. If it remains too long, shave off incremental amounts until it fits snugly with no gaps. Attach it with finish nails.
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