How to Repair Exterior Window Molding


Window molding is not just decorative, it also blocks the gap between the window's frame and the window opening. The exposed exterior molding around your windows can become rotted and damaged over time. Exposure to moisture and harmful ultraviolet (UV) rays can break down the wood fibers. Exterior window molding can be repaired by removing any damaged wood fiber and then filling the void created with an epoxy-based filling compound. In cases where the window molding is badly damaged, it may be necessary to remove the window molding and replace it with new material.

Things You'll Need

  • Claw hammer
  • Paint scraper
  • Die grinder
  • Core box router bit
  • Moisture meter
  • Drill
  • Assorted bits
  • Borate wood preservative
  • Injector
  • Paintbrush
  • Epoxy primer
  • Paper towels
  • Plastic board
  • Plastic putty knife
  • 2-part epoxy filling compound
  • 80- and 100-grit sandpaper
  • Acrylic primer
  • Acrylic exterior paint
  • Utility knife
  • Pry bar
  • Slater's ripper
  • Tape measure
  • Miter box saw
  • Finish nails
  • Wood putty
  • Caulking
  • Caulking gun
  • Window trim
  • Pencil

Repairing Damaged Molding with Epoxy Filler

  • Remove the rotted or damaged material. Use the claw end of your hammer to pull away loose material. Use a die grinder fitted with a core box router bit to grind away all of the damaged material and expose fresh, integrated wood fibers.

  • Measure the moisture content of the wood with a moisture meter. The moisture content must be below 18 percent for the two-part epoxy molding compound to work properly.

  • Drill several holes about 1 inch deep into the exposed, healthy wood and use a plastic injector to inject borate wood preservative into the holes. The preservative will help prevent the wood from continuing to rot after the epoxy has been applied.

  • Apply a coat of two-part epoxy primer, using a paintbrush. Cover the surfaces of the wood onto which the two-part epoxy filling compound will be applied. Let the primer dry according to the manufacturer's instructions before applying the filler.

  • Mix the two-part epoxy filler on a plastic board. Use a plastic putty knife to mix the filling compound.

  • Apply the epoxy filler to the window molding. Use the plastic putty knife to roughly shape the filler. Let the filler dry according to the manufacturer's instructions.

  • Sand the dried filler first with a piece of 80-grit sandpaper and then with 100-grit sandpaper. Work the repair until the filler is smooth and flush with the surface of the window molding.

  • Apply a single coat of acrylic primer with a paintbrush, followed by two coats of exterior acrylic paint in the color of your choice.

Replacing Badly Damaged Window Trim

  • Cut away any caulking or sealant from around the outside edges of the window molding with a utility knife.

  • Lift the badly damaged window molding carefully from the side of the house, using a pry bar. Lift the piece until the nails are exposed, then use a slater's ripper to pull the nails and the molding free. A slater's ripper is a hooked tool that can be slid underneath the trim to grab and pull the exposed nail shafts free.

  • Measure the length of the window trim with a tape measure and mark the replacement trim with a pencil. Cut the new window molding to size with a miter box saw. Nail the trim in place with a hammer and finish nails driven about 12 inches apart.

  • Set the nails and fill the holes with wood filler. Use a putty knife to spread wood filler over the exposed nail holes. Let the filler dry completely.

  • Sand the filled holes smooth with a piece of 100-grit sandpaper.

  • Apply a single coat of acrylic primer with a paintbrush, followed by two coats of exterior acrylic house paint in the color of your choice.

  • Run a bead of caulking along the outside edges of the new window molding.

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