Repair a Deck Board

Deck boards fail from rot, splits, or UV damage long before the structure underneath gives out. One compromised board threatens nothing but your foot if you step through it, but ignore it and water finds its way into the joists. The fix is straightforward: cut out the bad section, reinforce if necessary, and drop in new lumber. You are not rebuilding the deck. You are performing targeted surgery on a single plank. The key is matching what is already there. If your deck is twenty years old and built with pressure-treated southern yellow pine, a brand-new board in the same species will look glaringly different for about a year until the sun evens things out. Live with it or stain to match. If your deck uses hidden fasteners, you will need to buy a few clips. If it uses screws, use screws. The board does not care about aesthetics, but you probably do.

1. Mark joist centers first. Find solid joists on either side of the damaged section. The new board needs to land on the center of a joist at each end, so measure from the edge of the damaged area to the nearest joist center and mark your cut line there. Use a speed square to draw a perpendicular line across the board. Repeat on the other end.
2. Extract the rot cleanly. Set your circular saw to the depth of the deck board and plunge-cut along each line. Stop the cut about an inch from the edge to avoid overrunning into good wood. Finish the corners with a jigsaw or oscillating tool. Pry out the bad section with a flat bar.
3. Probe for hidden rot. Check the exposed joists for rot or softness by probing with a screwdriver. Solid wood resists; punky wood caves. If the joist is compromised, sister a new joist alongside it by bolting or screwing a matching-sized board to the existing joist with 3-inch structural screws every 12 inches.
4. Support unsupported ends. If your cut line does not land on a joist, install a perpendicular block between the nearest joists to support the board end. Cut a piece of 2x lumber to fit snugly between joists, then toe-screw it in place. The block should sit flush with the top of the joists.
5. Measure twice, cut once. Measure the gap precisely and cut your replacement board to length. Test-fit it in place. The board should drop in with about 1/8-inch clearance on each end. If it binds, trim it down. If it is too short, you cut wrong and need a longer piece.
6. Secure with matching fasteners. Position the board with proper spacing gaps on each side to match the rest of the deck. Drive two fasteners at each joist, positioned about three-quarters of an inch from each edge. Predrill if using screws in hardwood or near board ends. Countersink the heads flush with the surface.
7. Seal all exposed wood. Smooth any rough cut edges with 80-grit sandpaper. Apply a wood preservative or deck sealant to all freshly cut ends and surfaces. This step is non-negotiable for pressure-treated wood, where the factory treatment does not penetrate cut surfaces.
8. Catch problems before they spread. While you have tools out, walk the deck and check for any popped nails or loose screws. Tighten or replace as needed. One failing board often means others are close behind.