Cold Joint

A cold joint is an unintended, weakened plane that forms when a layer of concrete hardens (or stiffens past the point of monolithic re-vibration) before the next layer is placed against it, so the two layers do not knit into a continuous mass. It typically results from supply interruptions, plant breakdown, slow placing, or delays exceeding the concrete's initial set, and shows as a visible line with reduced bond, shear capacity and watertightness across the plane — a serious concern in water-retaining and exposed structures.

Unlike a planned construction joint (located, prepared and reinforced per IS 456 Cl. 13.4 at a point of low shear), a cold joint occurs at a random, often unfavourable location. Prevention is logistical: continuous supply, adequate placing rate, retarders in hot weather, and placing/re-vibrating successive layers before the underlying layer takes initial set. If one occurs, it must be assessed and treated as a construction joint after the fact — cutting back to sound concrete, roughening, cleaning and bonding — and may require structural review or repair where shear/water-tightness is critical.