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Expansion joints

Typically there here are two types of joints in concrete slabs, Expansion Joints and Controlled Crack Joints. Concrete slabs inside or outside above eight feet by eight feet generally have joints.

Expansion Joints provides space between concrete slabs. The space serves as abuffer for expansion on hot days and compression in cold days. Usually these Control Joints are installed during the initial installation of the concrete. Most control Joints are made of wood or some soft material so they can move with the expansion andcompression of the concrete. However the wood and expansion joint material quickly deteriorates and allows water under the slab which causes more cracks in the main slab. Usually Control Joints vary in size from half-inch to an inch in width (sometime a full 2x4 width) and three to four inches in depth. A slab without control joints will crack and reduce the life of the concrete slab. Control joints also serve as Controlled Crack Joints as the slab settles with time. Note water leakage causes more severe settling of the slab.


Controlled Crack Joints control cracking as the slab settles with time. Usually these Joints are cut into the slab after the concrete hardens. Control Joints vary insize from one-eighth inch to one-quarter inch in width and half inch in depth. A slab without Crack Joints will crack in random patterns and will reduce the life of the concrete slab. However the control joints are usually not installed deep enough to insure cracking along the joint and cracks occur randomly.

Both type of joints with time will accumulate dirt, salt, allow grass or weeds to grow,and allow water to filter under the slab, etc. Water under the slab accelerates thesettling of the concrete slab creating uneven concrete surfaces and cracks


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