How to Fix Damaged Expansion Joints in Concrete

✔ Step-by-Step: How to Fix Damaged Expansion Joints in Concrete

1. 1

   Inspect and Clear the Joint Line

   Examine the expansion joint for cracking, crumbling, open gaps, or edge damage. Use a joint rake, chisel, or pressure washer to remove loose material, old filler, sealant, and debris. This step is crucial — clean sides allow new filler or sealant to bond properly and prevent further movement damage.

2. 2

   Cut or Chase the Joint Cleanly (If Needed)

   If edges are chipped or uneven, use a concrete saw or crack chaser to re-cut the joint square and straight. This helps form a uniform repair channel. Ideal width is 10–20 mm, with depth of 25 mm or more depending on joint width and movement requirements. Use PPE and vacuum dust immediately after cutting.

3. 3

   Install Backer Rod for Correct Sealant Depth

   Backer rod is a compressible foam insert that controls sealant depth and gives it a firm base. Choose a rod 25–50% wider than the joint so it fits snugly. Press it down to the correct depth using a blunt tool. The sealant should be about 12 mm deep for most exterior slabs, and slightly domed on top.

4. 4

   Apply Bond Breaker Tape to Vertical Joints (Optional)

   For vertical joints or expansion joints between wall and slab, apply bond breaker tape on one surface to prevent three-sided adhesion. This lets the sealant stretch without tearing. While optional for horizontal joints, it’s essential in vertical applications or where movement is high.

5. 5

   Select and Prepare the Right Sealant

   Choose a flexible polyurethane, polysulphide, or hybrid joint sealant designed for concrete slabs. Avoid rigid or hard-setting fillers. Mix or prepare your product as per manufacturer instructions. Use a cartridge gun for small areas, or a bulk pump for longer runs. Sealant should be UV-stable and traffic-rated if outdoors or under vehicles.

6. 6

   Inject or Trowel the Sealant Into the Joint

   Slowly fill the joint in a continuous run, starting from one end. Overfill slightly, then tool it down into a smooth, slightly concave profile. This helps shed water and prevents trip edges. Work quickly before the product skins. Clean any overflows with solvent and rag as needed.

7. 7

   Allow Full Cure Time Before Traffic

   Most sealants require 24–72 hours to fully cure depending on product and temperature. Avoid foot or vehicle traffic during this time to prevent tearing or distortion. If weather is poor, cover with plastic sheeting but allow venting to avoid condensation. Do not coat or seal over flexible joints unless compatible.

8. 8

   Inspect and Re-Seal Every Few Years

   Joint sealants don’t last forever. Check every 2–4 years for signs of cracking, pull-out, or surface weathering. Re-seal as needed, especially in high-traffic areas or exposed outdoor slabs. Long-term maintenance avoids costly slab movement, water ingress, or spalling around the joint edges.