Isolation Joint

An isolation joint (sometimes called an expansion joint) separates a concrete slab from a fixed element — a column, wall, footing, or another slab — so the two can move independently as they expand, contract, or settle. Without one, differential movement can crack the slab at that connection point.

Isolation joints are typically formed with a compressible filler material placed before the pour, rather than saw-cut afterward like a control joint.