Concrete crack repair with Epoxy Injection

So which material is better for repairing concrete cracks: epoxy or polyurethane foam? The answer isn't always clear-cut. In many cases, either material can accomplish the task, and applicators may simply choose the material they have the most experience with. But here are some general guidelines: If the crack needs to be structurally repaired and the area needs to be as strong or stronger than the concrete around it, use an epoxy. If the crack needs to be repaired only to prevent water leakage or the crack is actively leaking, a polyurethane is usually the best choice. Here's a look at the advantages and limitations of each material.

Epoxies

Epoxies for crack injection are available in a range of viscosities, from ultra-thin to paste-like (such as the Emecole Epoxy Crack Repair Products), to accommodate cracks of different widths. Coles advice is to use whatever viscosity is needed to inject a given crack at pressures less than 40 psi. The wider the crack, the thicker the material required.

The main advantage of epoxies is their amazing compressive strength, which at 12,000 psi or greater exceeds that of most concrete. That's why epoxies are the only choice for cracks requiring structural repair. However, epoxies cure very slowly, generally taking hours to harden. This can be an advantage because it allows time for the epoxy to flow into even the smallest crevices. On the other hand, its also possible for the epoxy to flow out of the backside of the crack before it has hardened if the backfill outside the wall has separated from the foundation.

"Often there are voids behind cracks due to soil erosion or poor compaction," explains Cole. That's why the crack is leaking in the first place; its easy for water to enter.

Polyurethanes

If there is concern about material leaking out the back of a crack, polyurethane foams (such as Emecole Polyurethane) should be used. These elastomeric, fast-setting foams are effective alternatives for applications involving only crack sealing (waterproofing) and not structural repair. Because of their elastomeric nature, they are able to accommodate slight concrete movement so the seal stays intact. They also begin to harden and foam within minutes of injection. This reduces the chances of the material flowing out of an injected crack while still in liquid form, and even if some does leak out, the foam will fill the void.

"Urethanes are great for basic crack filling. They add practically zero compressive strength, but in most residential applications, you don't need it," says Cole.

Here are the basic steps for successful low-pressure crack injection. 

Keep in mind, however, that the type of epoxy or polyurethane used and the time required for injection will vary with each job depending on the crack width, wall thickness, and other conditions. These can also be bought as as crack repair kits that some with all the tools and supplies needed for the project.

Install injection ports: Surface Ports (short rigid-plastic tubes with a flat base) serve as handy entryways for getting the repair material into the crack. They eliminate the need to drill into the concrete, reducing labor time and cleanup. The base of the port is placed directly over the crack and bonded to the surface with an epoxy paste. A general rule-of-thumb is to space the ports an inch apart for each inch of wall thickness.

Seal the surface: Use an epoxy adhesive (such as Emecole Emecole 901 or Emecole 322) to seal over the surface ports and exposed cracks. The paste cures in about 20 to 45 minutes to provide a surface seal with excellent bond characteristics that holds up under injection pressures. The entire exposed crack is covered with the paste, leaving only the port holes uncovered.

Inject the crack: Begin injecting at the lowest port on the wall and continue until the epoxy or urethane begins to ooze out of the port above it. That's the visual sign that the crack has been filled to that level. Plug the first port with the cap provided and move up to the next port, repeating this procedure until the entire crack has been filled with epoxy or urethane. Let the compression spring on the dispensing tool push the material into the crack using slow, constant pressure. This will reduce the possibility of leaks or blow-outs and allow time for the repair material to fully penetrate the crack.

Remove the ports: Allow 24 to 48 hours at room temperature for the epoxy or polyurethane to cure and penetrate into the cracks. The injection ports can then be removed by striking them with a trowel or hammer. If appearance is an issue, the epoxy surface seal can be chipped away or ground off with a sanding disk. Another option is to use a surface seal that can simply be peeled off the wall after the repair is fully cured. Emecole manufactures a polyurea-based seal, Emecole 322 Seal-N-Peel, that develops a strong enough bond to allow the injector to do the work, but is flexible and can be peeled away when the job is done. Both Emecole 901, and 322 Seal-N-Peel are available in the crack repair kits.