Expansion joint sealing is one of those things that nobody thinks about until it’s failing. The joint is designed to accommodate the movement that happens in every building and every concrete structure as materials expand and contract with temperature changes, settle over time, and respond to load. When the sealant in that joint fails – cracks, pulls away, or deteriorates – the joint stops doing its job and water, debris, and load transfer problems follow. Here’s what you need to know.
What Are Expansion Joints and Why Do They Need Sealing?
Expansion joints are purpose-designed gaps built into concrete slabs, walls, facades, and large structures to allow controlled movement. Without them, the stresses that build up from thermal expansion and contraction, structural settlement, and load variation would cause cracking in unpredictable locations. Essentially, then, the joint is simply the planned location for that movement to happen.
The sealant in an expansion joint has to flex repeatedly over the life of the building without failing. It needs to accommodate movement in both directions – compression as the structure expands and extension as it contracts – while also keeping water, dirt, and other materials out of the joint. That combination of demands rules out rigid fillers and requires a purpose-designed, high-movement elastomeric sealant.
Why Expansion Joint Sealant Fails
Expansion joint sealant failure is common, and it happens for a few predictable reasons. The most frequent is wrong product specification – a sealant with insufficient movement accommodation for the joint. For example, if the joint moves ±15mm and the sealant is only rated for ±25% of the joint width, the maths might not add up. Consequently, over thousands of movement cycles, the sealant fatigues at the edges where it bonds to the substrate.
Other common failure causes include:
- Poor substrate preparation before application – sealant applied to dusty, damp, or contaminated surfaces won’t bond properly
- Wrong joint geometry – a joint that’s too deep for its width forces the sealant into three-sided adhesion, which prevents it from flexing correctly
- Age and UV degradation – external expansion joints take continuous UV and weathering exposure; sealants that aren’t formulated for this break down
- Physical damage – impact, foot traffic over joints, or debris compaction in open joints accelerates deterioration
- Wrong backer rod or no backer rod – the foam backing that sets the correct joint depth is critical to correct performance
Reference: Standards Australia – Sealant performance standards for construction joints
| 🔧 Seal’em Solutions – External Joint Sealing
Facade joints, expansion joints, external cladding, glazing perimeters, and weatherproofing. Rope access available for high-rise buildings where ground access isn’t possible. |
Types of Expansion Joints That Need Sealing
Overall, expansion joint sealing comes up across a wide range of building types and applications in Australia:
- Concrete slab expansion joints – in car parks, podium decks, ground-level slabs, and industrial floors; often subject to vehicle loading and water exposure
- Facade expansion joints – in precast concrete panels, masonry facades, and cladding systems; must accommodate thermal movement across the full face of the building
- Roof expansion joints – where roof sections meet or where roof meets parapet; critical waterproofing joints
- Bridge and civil expansion joints – in road bridges, pedestrian bridges, and infrastructure; high movement and heavy load requirements
- Structural movement joints in commercial buildings – at building perimeter joints, between different structural sections, or where old and new construction meet
How Expansion Joint Remediation Works
When expansion joint sealant has failed, the remediation process follows a consistent sequence. First, full removal of the existing sealant – partial removal over the top of failed sealant doesn’t work, because the new sealant bonds to the old material rather than the substrate. Second, substrate preparation – cleaning, priming where required, and installing or replacing backer rod to the correct specification. Third, application of the correct sealant product for the joint dimensions and movement requirements. Fourth, tooling and curing.
On commercial and infrastructure projects, the product selection and installation must be documented. This is particularly important for car park and podium deck joints where the sealant is part of the waterproofing system
| 🔧 Seal’em Solutions – Remedial Joint Sealing
We assess, remove, and replace failing sealant across all building types. Full condition report provided. Workmanship documented for strata and body corporate records. Working in QLD, NSW, and VIC. |
What Product Is Used for Expansion Joint Sealing?
The right product depends on the movement requirement, the substrate, and whether the joint needs to be painted or is in a fire-rated assembly. For most commercial and civil expansion joints, a high-movement polyurethane or MS polymer sealant is the correct specification – both offer the movement accommodation, durability, and substrate adhesion required for structural expansion joints. For fire-rated expansion joints, the product must be certified under AS 1530.4 for the specific joint configuration.
Seal’em Solutions specifies products based on the joint – not based on what’s easiest or cheapest. Getting the product right at the start is what determines whether the repair lasts 10 years or 10 months.
Does Your Building Have Failing Expansion Joints?
Common signs include water ingress at or below joint locations, visible cracking or separation at joint edges, debris and dirt compacted into joints, or sealant that’s become hard and brittle rather than flexible. If you’re seeing any of these, a professional assessment is the first step.
Book an expansion joint assessment →