How to Repair Clapboard

Repair the cracked ends of the clapboards by gently prying open the cracks with a putty knife of a flat pry bar. Spread construction adhesive or waterproof wood glue, like resorcinol, into the opening and press the wood back into place. To clamp the seam back into place, blunt the ends of several six-penny finishing nails by striking the points with a hammer. Blunting the nails will prevent them from splitting the undamaged clapboard pieces. Drive the nails into the clapboard in a row below the crack. Bend the nails slightly upward to apply pressure. Remove the nails once the glue is dry and fill in the holes with waterproof putty or paint.

Repair clapboards with warped ends that curve outward from the wall by refastening them to the studs behind them using either single 2 ¼-inch drywall screws of seven-penny (2 ¼- inch) galvanized siding nails. Drill a pilot hole 1/8th of an inch in diameter for each nail through the clapboard, but not into the stud. This will help avoid splitting the undamaged wood pieces. Hide the fastener by sinking it 1/8th of an inch below the surface and filling the hole with waterproof putty. Apply caulking compound to the seam and touch up the area with paint.

Replace any sections of clapboard that are too damaged to be repaired. Mark the section that you need to remove so that the end lies over the center of a stud, allowing you to nail the replacement piece directly into the stud. If you are replacing a section of clapboard with no stud behind it, cut the end of the adjacent piece back to the center of a stud and replace both sections with a single piece of clapboard.

Drive thick wedges of scrap wood under the ends of the section to protect the undamaged clapboard below. Cut across the exposed part of the section at each end using a back saw. Reposition the scrap wedges so they raise the clapboard overlapping one of the cuts. Use a keyhole saw to finish cutting the end. Insert the blade of the keyhole saw beneath the overlapping piece of clapboard.

Remove any visible nails with a flat pry bar. Use the pry bar to raise the section containing the nails by levering it upward. Place small scraps of wood under the pry bar to prevent scratching the undamaged clapboards. Remove the pry bar and strike the raised piece swiftly with your hands to force the clapboard back into its original position. Pry out the protruding nails, and the damaged section should slide out easily. Remove exposed portions of the damaged section with a hammer and wood chisel.

Cut new sections of clapboard to fit snugly in place. If you are cutting a piece more than 48 inches long, cut it 1/16th of an inch longer than you need. Coat the ends with primer and allow to dry. Slide the new piece under the overlapping clapboard until it's even on each side. If the piece is oversize, bend it slightly when setting it so that the center bows out and it will straighten when you release it.

Attach the new section with a seven-penny siding nail on each end and any place where a nail penetrates a stud. Prevent splitting by drilling pilot holes first. Recess the nails (if necessary), caulk the ends and apply the finish.