Exterior trim is a natural target for dry rot. Precipitation, such as rain, sleet and snow, is often the culprit, but other factors can lead to dry rot in exterior trim pieces. Lawn sprinklers that continually spray water on windows and doors on the outside can lead to dry rot, as can runoff or leaks from overhead rain gutters. All of these factors should be corrected to prevent future problems, but the existing dry rot must be repaired in order to salvage the exterior trim.

Instructions.Things You'll Need:
•Safety glasses or goggles
•Probing tool (pocket knife, screwdriver, awl, ice pick)
•Wood chisel and hammer
•Wood preservative or fungicide and rubber gloves
•Wood filler (wood putty, epoxy; polyester wood filler)
•Putty knife (metal or plastic)
•Sandpaper (medium- and fine-grit)
•Paintbrush
•Primer
•Exterior paint to match original trim color
Step
1Wear safety glasses or goggles. Use probing tool to identify all dry rot in the exterior trim. The wood will be soft and spongy. Use wood chisel and hammer to dig out dry rot, making sure to remove all affected wood.

Step
2Put on rubber gloves and apply wood preservatives or fungicide to the area where dry rot has been removed. Allow to dry per the manufacturer instructions.

Step
3Fill void with wood filler, pressing firmly with a putty knife to bond putty to the solid wood. Use enough filler to bring its top surface to a level slightly above surrounding exterior trim, up to 1/4 inch. Allow to dry per manufacturer instructions.

Step
4Use medium-grit sandpaper to sand down dried wood filler flush with surrounding exterior trim. Use fine-grit sandpaper to feather together edges of wood filler and exterior trim.

Step
5Apply primer to the repaired area of exterior trim with paint brush. Allow to dry per the manufacturer instructions. Paint repaired trim with exterior paint, blending new paint in with surrounding trim.