What Filler Can I Use for Gaps in Clapboard Siding?

Seal large gaps between the horizontal edges of clapboards. Insert a tube of construction adhesive, approved for exterior applications, into a caulking gun. Cut the tip of the adhesive tube off with a pair of scissors. Place the tip against the space where the bottom of the upper clapboard overlaps the lower plank. Pull the trigger on the caulking gun until adhesive begins filling the space between the boards. Move the calking gun along the length of the boards until the gap is filled with adhesive.

Drill a pilot hole near the bottom edge of the upper clapboard, adjacent to the adhesive-filled gap, with a one-eighth-inch drill bit. Install a one-fourth-inch diameter wood screw with a screwdriver through the edge of the upper clapboard and into the edge of the lower board, drawing the boards together. Wipe excessive adhesive from the clapboards with a damp cloth.

Insert a tube of paintable silicone-based caulking into the caulking gun and cut the tube tip to a one-fourth-inch bead. Fill the vertical gaps between the ends of clapboards with a caulking. Wipe excessive caulking from the top of the clapboards with a damp cloth.

Trowel wood filler over nail and screw holes with a putty knife. Allow the filler to cure according to the product instructions. Sand the cured filler with 220-grit sandpaper before painting or staining.