Archive for Thursday, October 3, 2013

Fix-it Chick: Repair or install concrete expansion joints

October 3, 2013


Expansion joints are created through the installation of a soft material, such as wood or foam, along the edges of concrete slabs.

The flexibility of these soft materials prevents damage that would otherwise occur as a result of weather-related expansion and contraction. Over time, the soft material deteriorates or becomes compressed and concrete is once again at risk of damage.

Driveways located at the base of a hill or on the downside of a sloping street are especially vulnerable to damage from compressed expansion joints.

Repairing existing or installing new expansion joints is a simple process that can save concrete from serious damage.

Step 1: Check existing expansion joints where structures or adjacent flatwork meet with the concrete slab. Large sections of concrete should have joints running across the full width of the slab, as well as down the center of particularly wide slabs. Joints should be at least 1/2-inch to 3/4-inch wide. Expansion joints should extend beyond the full depth of the concrete slab. Use a screwdriver to confirm that each joint at least 4-inches deep. Four inches is the minimum depth required for concrete driveways.

Step 2: Concrete contracts in cold weather. Choose a cool day to work on the concrete. Use a putty knife, chisel and/or vacuum to remove deteriorated materials from inside the existing joints and to clear away any accumulated dirt and debris.

Step 3: If necessary, use a concrete saw or chisel to increase the depth or width of existing expansion joints. Cut additional expansion joints into slabs with a cut-off saw equipped with a diamond blade. Use a chalk line to snap a straight guideline across the width of the slab. Follow the line with the concrete saw, keeping the blade wet to control the dust.

Step 4: Fill the new or existing expansion joints with pre-formed expansion joint strips or foam backer rod. Push the material firmly into the joint with a putty knife. A thin strip of western cedar or redwood may also be used to fill the void. Tap the wood into place with a hammer and sand or plane away any excess material. Do not force the wood into the joint.

Step 5: Seal the filled joint with a self-leveling urethane-based caulk specifically designed for use with concrete. Allow the sealer to cure completely before driving vehicles over the concrete slab.

— Linda Cottin can be reached at


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