How to Repair Bottom Split Cedar Siding on House

Strip the finish from the damaged cedar shakes or shingles. Use a pressure washer set to 1,500 to 2,000 psi, or sand the siding down with medium-grade sandpaper to strip the finish.

Fill in the splits with wood putty. If you are planning on painting the siding, you may also use waterproof Bondo putty. Scoop the putty out of its container with a putty knife, and spread it over the damaged part of the siding.

Work with the wood grain when spreading the putty. Check the bottoms of each shingle or shake to ensure that the putty completely fills every split. Allow the putty to dry.

Sand the putty down until it is flush with the rest of the wood. Use medium-grade sandpaper, around 100-grit. Wipe away the dust with a damp cloth.

Paint or stain the repaired shingles so they match the rest of the siding. Work with the grain. If you stain the siding, allow the stain to soak for about 30 seconds before wiping the excess off with a dry rag.

Apply a protective clear coat to the shingles when they are dry. Exterior polyurethane protects the wood from moisture and UV rays to help prevent further damage.

Spread the clear coat over the shingles or shakes with a soft-bristled paintbrush or a foam or lamb's wool applicator. Always work with the grain of the wood. Allow the first coat to dry.

Sand the clear coat down with 400-grit sandpaper. Sand just enough to roughen the surface. Wipe away the dust, and apply a second coat. Allow it to dry.