Joints in concrete flatwork help to minimize uncontrolled cracking. But if joints aren't properly planned cracks may still occur and mar the appearance of an otherwise good quality concrete job. When an area is irregularly shaped it is particularly important to carefully plan joint configurations that will avoid the common causes of cracking.


Thin slabs will usually crack at closer intervals than thick slabs. Longer joint spacings can be used if the slab is reinforced. Long narrow slabs tend to crack more than square ones. When it isn't practical to plan nearly square panels, the long dimension shouldn't be more than 1.5 times the short dimension. Re-entrant (inside) corners almost always cause cracking. Control joints and isolation joints should terminate at the edge of the slab or at an isolation joint, not at an intersecting control joint. Sharp acute angles should be avoided.