How to Fill Gaps in Sidewalk Slabs


Gaps can form in a sidewalk slab when underground pressure is not adequately absorbed by the foundation, or if the surface is exposed to a heavier weight load than it was built for. Unrepaired gaps and cracks are an eyesore, and a trip hazard. It only takes a few hours and basic materials to fill sidewalk gaps and make the surface safe and attractive.

Things You'll Need

  • Chisel
  • Hammer
  • Wire brush
  • Measuring stick
  • Paint brush
  • Bonding adhesive
  • Putty knife
  • Vinyl reinforced patch compound or fortified sand mix concrete
  • Wooden stirrer
  • Trowel
  • Burlap
  • Widen the bottom of the gap with a chisel and hammer. Place the tip of the chisel at an angle against the inner wall of the gap and hit the flat end with a hammer. Chip down the length of the gap.

  • Scoop chunks and debris from inside of the gap with a wire brush.

  • Measure the surface width and depth of the gap with a measuring stick. If it is deeper than 1/2 inch, fill the bottom until it is 1/2 inch from the sidewalk surface.

  • Add a light coat of bonding adhesive inside and around the surface of the gap with a paint brush. The adhesive helps strengthen the bond between the fill and the sidewalk.

  • Stir a container of vinyl-reinforced concrete patching compound with a wooden stirrer. If the surface of the gap is less than 1/2 inch wide, use a putty knife to fill the remaining 1/2 inch expanse of the gap.

  • Smooth the compound around the surface of the gap with a trowel to make the filled gap even with the sidewalk.

  • Stir pre-made sand mix concrete with concrete fortifier if the surface of the gap is wider than 1/2 inch. Fill the remaining 1/2-inch gap with the fortified sand concrete instead of the vinyl patching compound. Smooth the concrete over the sidewalk so the surface is even.

  • Cover the patched gap with moist burlap to dry it slowly. The added moisture prevents the fill from absorbing moisture from the old concrete.

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