Epoxy Injection for Cracked Concrete

1) Start by assuring that epoxy injection of the crack is appropriate — it is for structural repairs not sealing. You need to know the cause of the crack. If the reason the concrete cracked hasn’t been corrected, then it will crack again. Epoxy injection will not repair corrosion-induced cracks —they will come back.

2) Clean the crack and the surface adjacent to the crack. Remove all unsound concrete with a handheld wire brush. Power grinders or brushes create dust that can make it hard for the epoxy to bond inside the crack and for the cap to bond to the surface. Clean inside the crack using compressed air or vacuums.

3) Install the injection and venting ports. Some ports require drilling into the crack and some are surface-mounted, which are adequate for most cracks. Spacing of the ports is typically 8 inches, but can be farther with a wider crack. Ports can be installed on just one side of a concrete member or on both sides.

4) Failing to properly cap or seal a crack leads to a leak that will waste costly epoxy resin. Use a fast-curing gel-type epoxy. Where a crack goes through the concrete element, seal the crack on both sides. Be sure the surface is dust-free; brush with a 2-inch paint brush. Apply the cap 1/8 inch thick and 1 inch wide. Avoid skips and thin spots.

5) Make sure the epoxy is well mixed. Start at the crack’s widest part. Use injection equipment that can achieve high pressures (200 psi) with the low-viscosity material but control the pressure to prevent blowouts. Inject epoxy until refusal or an adjacent port begins to bleed epoxy. Cap the port and move to the next.

6) Continue the injection until no more epoxy can be forced into the concrete. If it’s still flowing, it’s still penetrating the cracks. After curing, remove the cap by grinding, or leave it if the owner doesn’t mind or it will be covered. The cap is only formwork, not part of the repair. To assure penetration, take 2-inch diameter cores — every 100 feet for floor cracks.

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