Expansion Joint
A deliberate gap through a structure that allows adjacent parts to move independently under thermal and structural movement.
On an actual building
It only works if the sealing system can accommodate the design movement. Filling one with rigid mortar defeats its purpose and transfers movement into the concrete either side, cracking it.
What we most often have to correct
That a gap in a building is a defect to be filled. It is a designed feature, and filling it rigidly causes the damage it was designed to prevent.
Terms that come up alongside this one
- Construction Joint
The interface where one concrete pour meets a previous one that has already set..
- Backer Rod
A closed-cell foam rod pressed into a joint before sealant, setting the correct sealant depth and preventing it bonding to the joint base..
- Sealant Movement Capability
The percentage of a joint's width that a sealant can accommodate in extension and compression without failing, stated by the manufacturer..
Expansion Joint — questions we get asked
What does expansion joint mean in waterproofing?
A deliberate gap through a structure that allows adjacent parts to move independently under thermal and structural movement.
Why does expansion joint matter on a real project?
It only works if the sealing system can accommodate the design movement. Filling one with rigid mortar defeats its purpose and transfers movement into the concrete either side, cracking it.
What do people commonly get wrong about expansion joint?
That a gap in a building is a defect to be filled. It is a designed feature, and filling it rigidly causes the damage it was designed to prevent.
Have a building showing this?
If a term on this page describes something you are looking at, a site inspection will tell you how far it has gone and what it needs. It costs nothing.
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