▽ +09.00Problem · Joints
The expansion joint is leaking
Water or damp along the joint line on a soffit or wall, or a sealant that has cracked or pulled away.
What you see
- A wet line along the joint, seen from below
- Sealant cracked, hardened or detached from one side
- Broken joint edges
- Loose or noisy cover plates in car parks
- Tiles or screed cracked along the joint line
Possible causes
Sealant beyond its life or movement capability
Sealants harden, crack and lose adhesion with time and movement.
Three-sided adhesion or wrong geometry
Without a backer rod and the right width-to-depth ratio, the sealant tears.
A joint covered by rigid finishes
Tiles or screed laid over the joint crack and open a path for water.
Traffic damage
Wheels break the edges and loosen the covers.
A discontinuous waterproofing tape
At intersections and upstands, where installation is hardest.
How it is diagnosed
The diagnosis confirms the cause before any repair is chosen.
Trace the joint
Follow it through the roof, walls and floors; leaks often come from an intersection.
Check the sealant
Adhesion, cracks and hardness along its length.
Measure the gap
Compare the joint width with the design and the seasonal movement.
Water test
A controlled test on a section of the joint locates the entry point.
- Elastomeric sealant
- Backer rod
- Joint waterproofing tape
Possible solutions
The fix follows the diagnosis; these are the common options and their systems.
Renewing the joint system
Edge repair, backer rod, sealant, tape and cover.
Systems
Edge repair
Broken edges rebuilt with repair mortar.
Systems
Re-detailing the waterproofing at the joint
Continuity of the roof or deck system across the joint.
Systems
What not to do
- Filling the joint with mortar, epoxy or a rigid sealant
- Injecting the joint with a rigid resin
- Fixing cover plates on both sides
- Tiling straight over the joint
General educational content; final values and requirements follow the manufacturer’s TDS and the approved project specification.
Common questions
Can the joint be sealed with silicone?
Only with a sealant rated for the joint’s movement and exposure; the joint geometry and backer rod matter as much as the product.
Why does joint sealant crack or come away?
Because of a wrong width-to-depth ratio, a missing backer rod so the sealant bonds on three sides, no primer, UV ageing, or movement beyond what the material can take.
Technical inspection
Need a diagnosis for your case?
Send photos, a description and the location; our engineers identify the cause and the fix after an inspection.