What is an Isolation Joint?
An isolation joint is a separation of an existing concrete slab from a new concrete slab or wall. A piece of expansion joint (usually ½” wide and made of cork or recycled fiber material) is placed against the existing concrete slab and when the new concrete slab is poured, this expansion joint separates the two slabs.
Why is an Isolation Joint Necessary?
Concrete is known to expand and contract. When two concrete slabs are poured against one another, they will expand and contract separately and exert forces on one another. This differential movement can cause the concrete to crack. The expansion joint material between the two slabs allows this expansion and contraction to occur independently and reduces the chances of cracks forming. It is also worth noting that isolation joints are not just necessary for slab against slab pours. Isolation joints should be installed when pouring concrete up against structures such as walls and buildings.