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Crack repairs

Cracks are the perpetual problem of concrete-everyone knows the jokes about cracked concrete: there are only two kinds, concrete that has cracked and concrete that will crack. Basically, though it's true and so we deal with the cracking.

There are a bunch of reasons concrete cracks, but that's a topic for another day. In this section we are talking about repairing cracks. Learn more about preventing concrete cracks.

Let's start with thin surface cracks, also called plastic shrinkage cracks. These really can't be repaired and the only reason to do anything is appearance, since they don't affect the concrete's performance. If the slabs owner really hates the appearance of the plastic shrinkage cracks, a thin overlay can be installed.

Overlays can also be used to cover other cracks in slabs-especially drying shrinkage cracks which typically don't move once the initial mixing water has dried out of the slab. Be sure to prepare the surface, which includes bridging over any cracks. But first, make sure the concrete is sound-an overlay on poor concrete will fail, especially if there is settlement due to poor subgrade compaction. That might be grounds for looking into slab jacking. Learn more about thin overlays or more information on installing thin overlays or microtoppings.

Another way of "fixing" nonstructural cracks-such as shrinkage cracks-is to route the crack out with a crack chaser (or a saw or angle grinder) and fill it with a sealant. The idea is to open the cracks up and create a vertical face to a depth of ¼ to 1 inch (3/4 inch is often specified as the minimum). This new joint is then filled with a sealant. For floors, it needs to be rigid enough to support any loads but still have some flexibility.

A great material for crack sealing is a polyurea. These relatively new materials behave much like epoxies in their ability to adhere to the concrete, but this material can be installed over a wider temperature range and cure very rapidly. Emecole is a great source of information on joint repair sealants. Note that this type of sealant is designed to have a lower bond strength to the edges of the crack or joint to prevent new cracks from forming adjacent to the repair. If the crack or joint moves, the sealant's bond fails first, not the concrete.

One way to disguise cracks in a slab is to incorporate them into a decorative design. See how one contractor uses cracks to achieve a rustic look.

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