How to Repair a Gap Between Your Sidewalk and Foundation

Assess the Gap

Measure the width and depth of the separation to determine whether it's a cosmetic joint or a structural issue caused by settlement, erosion, or improper installation.

Choose the Right Material

For small, dry gaps (<1/4 in) a flexible polyurethane sealant works well; larger or moisture‑prone gaps need a cement‑based backer rod topped with polymer‑modified concrete or mortar.

Prepare the Area

Clear debris, loose soil, and vegetation. Cut back any cracked concrete to sound material, and wet the substrate lightly to improve adhesion.

Install Backer Rod (if needed)

Insert a foam backer rod into the gap, pressing it in so it sits slightly below the surface. This provides a backing for the sealant and controls depth.

Apply Sealant or Mortar

Using a caulking gun, push polyurethane sealant into the joint, smoothing with a putty knife. For cement‑based repairs, mix mortar to a workable consistency, press it into the gap, and finish with a trowel to match the sidewalk profile.

Cure and Protect

Allow the sealant to cure per manufacturer instructions (typically 24 hours). Keep the area dry and avoid foot traffic until fully set.

Prevent Future Gaps

Maintain proper drainage away from the foundation, repair any grading issues, and seal expansion joints regularly to accommodate movement.