Cracks in concrete exposed to moisture should be repaired as quickly as possible to avoid more extensive and expensive damage. These cracks can be caused by drying shrinkage; improper control, construction, and/or isolation joints; foundation settlement; or other structural changes. Determining if the crack is dormant or if it is moving and growing also impacts the method of repair. Finally, aesthetics plays a part in the repair procedure.

Sound concrete that is dormant or can be prevented from moving can be repaired through EPOXY INJECTION. Cracks as narrow as .002 can be effectively injected. This is a permanent form of repair the restores structural integrity and protects the concrete from damaging water intrusion.

Routing and sealing is the most common method of crack repair. In this procedure the crack is enlarged to permit the complete penetration of the repair compound. This method is most effective when a structural epoxy is gravity fed into the crack to return the slab to its original monolithic state, with all the structural properties unaltered. When this type of cracking is caused by improper joint placement, new joints should be cut and sealed to ensure a long-term repair. This method is excellent for secondary containment systems, warehouses, and distribution centers.

Flexible sealing using an elastomeric sealant will allow for movement in a crack that is still moving. The advantage to using a flexible sealant is that new joints do not have to be cut. The disadvantage is that elastomeric joint sealants are often not durable enough to handle heavy traffic. More expensive two-component urethane sealants can be used, but joints must meet depth and width criteria specific to the sealant.

With the development of high-molecular-weight-methacrylate monomers cracking in large slabs can be sealed and "healed" in one application. HMWM is a very low viscosity liquid that has flow properties similar to diesel fuel. It is applied over the surface and easily penetrates and fills thin cracks. When cured it forms a rigid polymer that structurally repairs cracks and also provides a sealer that protects the concrete against water intrusion. This is an excellent solution for parking structures, bridges, and traffic decks.

The above methods of crack repair fix the problem, but the cracks remain visible. To prepare cracks prior to resurfacing, the crack must be bridged to provide a bonding surface. In order to do this the crack is filled with structural epoxy, coated with an elastomeric, a fiber "bridge" is imbedded in the elastomeric coating and then recoated. Once this crack system is cured it is overlaid with quad-polymer-modified concrete 1/64"–1/32" thick. These cracks will then eventually blend into the existing concrete or a broom finish or decorative overlay can be applied—cracks are no longer visible and will not break through the overlay. This repair is so durable it can be used in high traffic areas, as well as, driveways, patios, lobbies, warehouses, office buildings, to name a few.

WE DO recommend that exterior cracking be addressed as soon as possible, but interior cracks not subject to high traffic, moisture, or excessive weight can often just be monitored to determine their structural impact, if any.

See also:
EPOXY INJECTION for a discussion of the benefits of this crack repair procedure. SPALL REPAIR for cracks with edges broken away. EXPANSION/CONTROL JOINTS for cracks caused by improper placement of joints. FOUNDATION SUPPORT SYSTEMS for cracks caused by settling foundations.

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