How to Repair Rotten Window Sills

Inspect your windows every spring for damage.

When a window sill gets wet, water may collect and damage the sill. Do a visual inspection every spring of your outside window sills to see if any have started to rot. Look for paint that is starting to bubble or flake. If your window sill has started to rot, you will need to repair it because the damage will worsen. This is not a big project and the repair kit you need typically is big enough to do more than one window, allowing you to use your new expertise again if needed.

Things You'll Need

• Hook style paint scraper
• Chisel
• Hammer
• Screw driver
• Epoxy wood filler repair kit
• Wood consolidant
• Putty knife
• Fine sandpaper
• Scrap wood or sanding block 4" x 6"
• Drill
• Drill bit 3/8-inch
• Coarse file or rasp
• Paint brush
• Exterior paint
• Exterior primer

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Instructions

1. Expose the area with rot by removing paint from both the window jamb and the sill. Use a hook-type scraper to clean off as much of the wood as you can. Since you have already found rotten wood on the window sill, be sure to check other parts of the window for wood rot. Rotted areas will look and feel damp and also feel soft.

2. 

   Use a chisel to remove rotten wood.

   Chisel away the rotten wood. Take a screwdriver and try to put it into the wood. If the screwdriver goes into the wood easily without trying hard, the wood is rotten and needs to be removed. Chisel out all of the soft wood. It is important to get out as much of the rotten wood as possible for a long-term repair.

3. Check to see if you have been able to remove all of the rotted wood. If you find there is some rot that cannot be removed, drill several 3/8-inch holes into the remaining wood. In your repair kit you might find wood consolidant. If your kit does not have any, you can purchase wood consolidant where you bought the epoxy kit. Apply the consolidant to the wood and allow it to dry. This will strengthen the remaining wood.

4. Mix the epoxy following the instructions on the repair kit. Fill the empty areas you have chiseled out, using the epoxy and a putty knife. Overfill the holes. Let dry completely. Check the instructions on the package of epoxy for the suggested length of drying time, usually at least four hours but could be overnight.

5. 

   Sand and shape the repaired area until smooth.

   Shape the repaired area of the sill, using the file or rasp, so that it matches the rest of the sill. Sand the flat areas with the sandpaper wrapped in a wood scrap or sanding block. Make sure you sand the area smooth.

6. 

   Use a good quality primer and exterior paint.

   Paint the repaired window, starting with an exterior primer. Use a primer of good quality because it has to protect an area of wood that already has been damaged. After the primer is thoroughly dry, apply several coats of a quality exterior paint to help protect the area from additional damage.

References

• Repair a Rotten Window Sill
• How to Repair a Rotten Window Sill