Expansion Joints 101: Why They Fail and How to Fix Them

Expansion joints are designed to accommodate the natural movement of buildings — thermal expansion, settling, and structural deflection. When they fail, water ingress, cracking, and cosmetic damage follow quickly. Here's what causes failure and how to address it properly.

Why Expansion Joints Fail

The most common causes of expansion joint failure are: using the wrong sealant (rigid products can't handle movement), poor substrate preparation (sealant won't bond to dirty or dusty surfaces), incorrect joint design (too narrow or too deep for the movement expected), and UV degradation over time — especially in Queensland's harsh climate.

The Importance of Backer Rod

A properly installed backer rod is essential for expansion joint performance. It controls sealant depth, creates the correct hour-glass profile for maximum flexibility, and prevents three-sided adhesion which is the leading cause of cohesive failure. We see many failed joints where backer rod was either missing or the wrong size.

Choosing the Right Sealant

External expansion joints typically require polyurethane (PU) or hybrid sealants rated for the expected movement class. A joint expected to move +/- 25% needs a sealant rated for that movement accommodation factor (MAF). Silicone is generally not suitable for external expansion joints due to dirt pick-up and limited paintability.

The Remediation Process

Proper expansion joint repair involves: complete strip-out of the failed sealant, cleaning and preparation of both faces, installation of correctly sized backer rod to the right depth, priming if required by the sealant manufacturer, and tooling the new sealant to a slightly concave profile for optimal stress distribution.

CaulkTech has extensive experience remediating expansion joints on buildings of all sizes across SEQ. We assess, specify, and install — with a focus on getting the joint design right so the repair lasts. Get in touch for a site assessment.