How to Repair Rotted Wood

Windowsill with rotten wood
bruceman / Getty Images
Project Overview
  • Working Time: 1 - 2 hrs
  • Total Time: 1 - 2 days
  • Skill Level: Intermediate
  • Estimated Cost: $10 to $50

If you catch rotted wood in time, you can successfully repair it with epoxy resin. Repairing rotted wood means you'll be able to stain or paint it again to blend in with the surrounding wood.

Rotted wood items that can be repaired partially include rotted wood moldings, trim, casing, siding, newel posts, fascia boards, balusters, and window frames and sills.

Before You Begin

Repairing rotted wood is a two-part process: preparation and patching. During the preparation phase, you'll need to remove as much of the rotted wood as possible. If the wood is wet or moldy, it must thoroughly dry out before the patching step.

During this phase, you can also evaluate whether the wood can be repaired or if it needs to be replaced.

Deep areas or areas that need moderate strengthening should be patched with two-part epoxy resin. First, a liquid epoxy wood consolidant is brushed onto the cleaned-up wood. Second, a moldable epoxy is applied to the missing wood area. After drying and sanding, the epoxy matches the level of the surrounding wood. It can then be stained or painted. 

Tip

Repairing rotted wood with epoxy is often more expensive than replacing it with wood. Calculate the size of the void by measuring length by width by depth to arrive at total cubic inches. An 8-ounce kit, which costs $30 to $35, can fill a little more than 14 cubic inches. On a volume basis, compare the cost of repairing the wood against the cost of replacing it with new wood.

Should You Replace or Repair Rotted Wood?

When considering whether to repair rotted wood, it's sometimes easier, less expensive, and safer to replace the wood. It's best to replace the wood if the item is structural and if the rot comprises about 15 percent or more of the item. For wood that's inexpensive and easy to find, you'll usually want to replace rather than repair it.

But if the item is personally or historically significant, you may want to try to repair it. You may even choose to repair some insignificant items simply due to the cost or complexity of replacing them. For example, it's usually best to repair rotted wood on a windowsill—it's difficult to remove and replace this piece, and repairs will not affect structural stability.

Repair Rotted Wood
  • Less than 15 percent of the wood needs to be repaired

  • Patched item is so significant that it's worth keeping

  • Replacing item is too difficult due to size or complexity

Replace Rotted Wood
  • Item is structural and repairing it will compromise its strength

  • Item cannot be painted, stained, or left as-is (repair patches are visible)

  • Wood is inexpensive and easily obtainable

What You'll Need

Equipment / Tools

  • Putty knife
  • Screwdriver
  • Five-in-one tool
  • Heat gun
  • Latex gloves
  • Sandpaper
  • Sanding block
  • Oscillating sander
  • Tack cloth
  • Chip brush

Materials

  • Two-part epoxy resin kit
  • Clean disposable plastic containers

Instructions

  1. Dry Wood Out

    Let the wood completely dry out. Exterior wood can sometimes take weeks during the dry season to dry out. It helps to cover the wood with clear sheet plastic, elevating the plastic from the rotten section to promote airflow.

  2. Remove Rot

    Removing the rot will help accelerate the drying process. Use a screwdriver, paint scraper, or five-in-one tool to carve out the rotted wood. All loose and unstable wood must be removed. If the wood still needs to dry out, let it dry naturally or carefully use a heat gun to dry out damp areas.

  3. Mix Consolidant

    In a plastic container, mix the two liquids with a wooden stick. Use a chip brush to brush the consolidant onto the wood. Apply heavily. The consolidant has about 30 minutes of working time.

    If the wood is heavily cracked or pitted, you can pour the consolidant into those deep voids.

  4. Let Consolidant Harden

    Let the consolidant cure for about two or three hours. In colder temperatures, it may take longer for the consolidant to harden.

  5. Mix Filler

    Epoxy filler consists of two parts (often called Part A and Part B) that harden when mixed. Wearing latex gloves, mix the two parts in a clean plastic container.

  6. Apply Filler

    Using the putty knife, generously apply the mixed filler to the missing wood area. Push the filler in firmly. Roughly sculpt the filler to the shape of the missing windowsill section. Make the shape slightly larger than the original.

  7. Sand Down Filler

    Let the filler harden for at least four hours. With rough, #100 sandpaper on the sander or sanding block, sand down the filler to the size of the original windowsill.

  8. Smooth Filler

    Switch to #220 sandpaper. Continue to sand down the filler until it is smooth.

  9. Paint or Stain Filler

    Clean dust off of the filled section with tack cloth. Paint or stain as desired.