Hardboard siding is a blend of wood, resin, and wax pressed together in a manner similar to paper mache. Many homeowners prefer hardboard for siding replacement because it is inexpensive and it won't shrink or swell like real wood. However, you may learn hardboard is still susceptible to holes and cracks. It is easy to fix the damaged hardboard planks without replacing all of the siding by following this guide.
Prepare to Fix the Siding
To patch the hardboard siding, you need:
- work gloves
- tape measure
- wire brush
- fine-grit sandpaper
- paint scraper
- putty knife
- drill (optional)
- pry bar
- two-inch galvanized nails or screws
- reciprocating saw (optional)
- wood filler or auto body filler patching compound
- small trowel
- replacement boards (optional)
Use the paint scraper to clean loose paint. Inspect the siding for loose nails, and hammer them in place. To fix the boards that won't stay down, hammer in one or two more nails beside the original nail.
Patch Holes and Cracks
Add filler or compound on the trowel, and spread it on the crack or hole with a putty knife; working it in to fit the shape of the damage. Smooth the putty, so it makes a one-inch overlap on the adjacent boards. Use a damp rag to clean excess filler.
Keep applying compound until you no longer see a recess. Let the compound dry, and lightly sand until the filler or compound is flush with the surface, then clean sand dust. If the hole is large, you may need to spread on an additional layer of filler or compound.
Replace Damaged Boards
Detach the cap trim, and use a pry bar to remove nails from damaged boards, or remove screws with a drill; saving the good hardware. You may have to remove several planks before you get to the damaged board. Finish prying the boards off with the pry bar.
Mark the length of damaged boards, if possible, shaping for fit around windows and other obstructions. Cut the new board to the needed size with the saw.
Fasten the cut board into place with the screws or nails; placing nails every eight inches on vertical panels. Start nailing lap boards (panels that are thicker on bottom) at the top part and bottom part to secure adjacent panels. Replace panels within two panels of the replacement board, even if they don't appear damaged.
Reinstall the cap trim and non-damaged boards. If desired, prime the siding with bonding primer, and paint the siding. Consider replacing badly damaged siding.