Keep your deck guest-worthy by filling small cracks.

How to Repair Cracks in Composite Decks

by Eric Jonas

Composite decking is made by combining byproducts of wood with resins and plastic. While composite wood is a durable, rot-resistant and crack-resistant material, it is not indestructible. Cracks happen, sometimes due to normal wear and tear and other times because your foundation has been settling underneath. If you come across a crack in your composite deck, don’t despair. You can patch up the crack and have the board looking brand new in no time.

Crawl under the deck or unscrew the cracked board and flip it over to check the underside. Inspect the board to make sure it has not cracked all the way through. If the damage is severe, the board might need to be replaced. If the crack is shallow, you can repair the flaw.

Return the board and screw it back into place. Clean out the crack by blowing air into it with a can of compressed air or an air nozzle attached to an air compressor. Use a thin, but dull-edged, putty knife to remove any debris the air cannot dislodge. Avoid sharp-edged knives to prevent making the crack larger or deeper.

Moisten a lint-free cloth with mineral spirits, clean out the crack, and then let it dry thoroughly. Dirt and debris in the crack can prevent the composite filler from adhering properly.

Apply strips of wide painter's tape or masking tape around the crack, exposing just the crack and as little as the rest of the composite material as possible.

Hold the tube of composite filler on a slight downward angle against the far edge of the crack. Squeeze gently to fill the crack with the composite. Squeeze along the crack until you reach the other end. Move back to the far edge of the crack and press down firmly with a putty knife to push the filler into the crack. Scrape the putty knife along the crack to remove excess filler and create a smooth surface.

Squeeze a little more filler into the crack if it is not filled level with the rest of the composite and then smooth it out again with the putty knife. Let the filler dry according to the manufacturer's instructions.

Pull off the painter's tape and sand the filled area with medium-grit sandpaper parallel to the composite board to smooth the filler. Stain the filled section with a stain that matches the composite board and allow it to dry before walking on the board.

Items you will need

  • Can of compressed air (or air compressor with air nozzle)
  • Dull-edged putty knife
  • Lint-free cloth
  • Mineral spirits
  • Painter’s tape (or masking tape)
  • Composite filler
  • Medium-grit sandpaper
  • Composite deck stain


  • Composite filler is available at many home improvement stores.


  • Building a Deck: Expert Advice From Start to Finish; Scott Schuttner
  • Building Decks and Porches; John Derossett, et al.

About the Author

Eric Jonas has been writing in small-business advertising and local community newsletters since 1998. Prior to his writing career, he became a licensed level II gas technician and continues to work in the field, also authoring educational newsletters for others in the business. Jonas is currently a graduate student with a Bachelor of Arts in English and rhetoric from McMaster University.

Photo Credits

  • Digital Vision./Photodisc/Getty Images