Hollow-core doors have a thin, outer skin of plywood or fiberboard glued to a narrow frame around the door's perimeter. Inside the frame, the door's thin panels are supported by cardboard or fiberboard strips. The assembled door is light, inexpensive and subject to accidental damage if hit by something hard or pointed. Small holes up to 5 inches wide are repairable, but larger holes make good-looking repairs difficult. Replacing the door is often the only option.
List of Items Needed
- Utility knife
- Low-expansion foam spray insulation
- Breakaway-blade utility knife
- Plaster mix
- 6-inch-wide putty knife
- Handheld oscillating tool
- 60-grit sandpaper
- Spackling paste
- 120-grit sandpaper
Cut the edges of the hole with the utility knife to remove broken bits of wood or fiberboard. Hole the knife at an angle to bevel the edges of the hole as you cut. Remove all broken or damaged pieces.
Crumple pieces of newspaper and fit them inside the door around the edges of the hole. The newspaper keeps the fillers at the repair site and prevents them from moving away from the hole.
Spray low-expansion foam into the hole and fill it about two-thirds full. Low-expansion foam does expand, but with less force than expanding foam. Wait for the foam to expand and begin to stiffen, then trim it off just below the surface of the door with the long blade on the breakaway utility knife. Wait for the foam to finish hardening.
Mix approximately 1/2 cup of plaster or enough to fill in over the hardened spray-foam insulation. Spread the plaster onto the repair area with the putty knife. Pull the edge of the putty knife over the hole to make the plaster flush with the surface of the door. Clean up plaster from the sides of the repair immediately.
Sand the plaster with the oscillating tool and 60-grit sandpaper to remove bumps and ridges. Avoid sanding beyond the edge of the repair more than necessary.
Apply a thin coat of spackling paste to the repair with the wide putty knife. Let the paste harden, then sand it smooth with 150-grit sandpaper. The repair is ready to prime and paint.
Tips and Warnings
- The repair process is easier if you lay the door flat.
- On small holes up to 1 1/2 inches in diameter, remove the broken pieces, then push some crumpled newspaper into the hole to serve as a backer. Fill in the hole with plaster filler, then a final coat of spackling paste, and sand it smooth.
- Prime the repair before you paint it. Primer allows the paint to adhere better.
- Wear safety glasses throughout the process and wear a dust mask while sanding.