Fixing Gouges, Cracks, and Splintering on a Composite Deck

Composite decking was supposed to be maintenance-free, but it isn't. A dropped tool, a winter freeze-thaw cycle, or just years of foot traffic leave marks. The good news: composite damage is almost always repairable without replacing the whole deck. The catch is knowing which tool fixes what. A surface splinter needs different treatment than a structural crack running through a board's thickness. Small gouges and surface splintering can be cosmetically restored in a few hours. Deeper cracks and structural damage require either filler injection or board replacement. This guide walks you through each damage type and the repair that actually works.

1. Know what you're fixing first. Walk the entire damaged area in daylight. For surface splinters and gouges, run your hand over the spot—if it's roughness only, surface repair applies. For cracks, press on both sides of the crack with your fingers; if the crack widens or the board flexes, it's structural. Measure crack length, width (use a feeler gauge if it's tight), and depth. Splinters that lift the surface need removal before filling. If more than 20 percent of a single board is damaged across its width, or if a crack runs the full length, replacement is cheaper than repair.
2. Dry wins repairs. Use a pressure washer set to 1,500 PSI or lower, angling the nozzle 45 degrees away from the damage to avoid forcing debris deeper. For splinters, brush the area with a stiff deck brush while still damp to raise and loosen fibers. Dry the entire repair zone with towels or let it sit in direct sun for 2 to 4 hours—composite fillers bond poorly to damp surfaces. For structural cracks, use a shop vacuum fitted with a brush attachment to clear out any dirt, mold, or loose composite particles from inside the crack.
3. Smooth the splinters away. For raised or rough splinters, use 80-grit sandpaper wrapped around a sanding block. Sand in the direction of the deck boards, not across them, using medium pressure to feather the splintered area into the surrounding surface. Check your progress with your hand every few passes. Stop when the area feels smooth and the fibers are no longer raised. Wipe away dust with a damp cloth and let dry again.
4. Pack gouges tight. For surface gouges or minor pitting less than 1/4 inch deep, use a two-part composite filler rated for exterior use (not generic wood filler—composite decks need specialized products). Mix according to package instructions, usually a 2:1 or 3:1 ratio of filler to hardener. Use a plastic putty knife to pack the filler into the gouge, overfilling slightly. Smooth with a wet putty knife, working in one direction. Allow the filler to cure per instructions, usually 24 hours, before sanding flush with 150-grit paper.
5. Seal cracks from inside. For cracks deeper than 1/4 inch or running along the board's length, use an epoxy injection system. First, clean the crack with a thin wire brush or compressed air to remove all loose material. Widen the crack slightly with a utility knife or diamond-blade crack chaser if it's narrower than 1/8 inch—epoxy needs material to grip. Mix two-part epoxy per instructions and load it into an injection gun or syringe applicator. Work slowly along the crack, filling from the deepest point upward, applying even pressure. Overfill the surface slightly. Once cured (usually 24 to 48 hours), sand flush with 150-grit paper.
6. Blend repairs invisibly. After fillers and epoxy are fully cured, use 150-grit sandpaper to feather the repair area into the surrounding composite deck. Sand in long strokes along the board grain, checking frequently that you're not sanding away surrounding material. Switch to 220-grit for a final pass to match the original texture. Wipe clean with a damp cloth. The repair should be invisible by touch; minor color variation is normal and will fade over time.
7. Match the original finish. If your composite deck was originally sealed or has a protective coating, the repair area needs matching treatment. Clean away all dust with a tack cloth. Apply a composite deck sealer or manufacturer-recommended clear coat to the filled or repaired area using a small brush, feathering outward to blend with surrounding sealed areas. Allow full cure time per sealer instructions before allowing foot traffic. Sealed repairs may require annual touch-ups.
8. Swap out broken boards. If a single board has multiple cracks, splinters covering more than 20 percent of its surface, or a structural crack running its full length, replacement is more reliable than repair. Turn off power to any deck lighting in the affected board. Remove fasteners using a power drill with a screwdriver bit or a fastener extraction tool. Lift out the damaged board. Install a replacement composite board of matching color and brand using stainless steel fasteners rated for composite decking (standard deck screws corrode). Space fasteners per manufacturer spec, usually 12 inches apart along joists, and countersink screw heads 1/8 inch below the surface if your deck system uses hidden fasteners.
9. Fix the source below. Cracks and splinters often signal moisture problems underneath. After repairs, inspect the underside of the deck from below, looking for rot in the framing, pooled water, or poor drainage. Clear debris from under the deck and ensure water can flow freely away from joists and support posts. If you see soft or discolored wood in the substructure, address that before the repaired composite boards fail again. Add or improve drainage, trim overhanging vegetation, or install additional under-deck ventilation if needed.
10. Seal against future damage. Once repairs are complete and fully cured, a preventative sealer or deck stain can protect against future damage and UV fading. Choose a product specifically rated for composite decking—not traditional wood stain. Clean the entire deck surface first with a composite deck cleaner, pressure wash, and allow to dry fully. Apply sealer per product instructions, usually with a roller or pump sprayer, in even coats. Cure time varies by product but typically ranges from 24 to 72 hours before use. Reapply every 2 to 3 years depending on climate and foot traffic.
11. Track repairs seasonally. Composite expands and contracts with temperature and humidity, especially at repair seams. Walk the deck quarterly and check filled or repaired areas for new cracks, shrinkage, or separation from surrounding material. In freeze-thaw climates, inspect after winter. If a repair has failed, the underlying cause—usually moisture or inadequate surface prep—needs correction before you repair again. Keep notes on which repairs required touch-ups and where; patterns reveal systemic problems like poor drainage or structural settling.