There are three rules when it comes to concrete: it won't catch on fire, no one is going to steal it, and it's going to CRACK! When pouring concrete slabs contractors use control joints and saw cuts to help control where the cracks occur, but they are not always a guarantee. A general rule of thumb when placing control joints is not to exceed 8-12 feet in any direction. When it comes to foundations, there are generally no control joints, expansion joints, or saw cuts. During construction, Continuous forms are placed, rebar is stationed inside the forms, concrete is poured, and J-Bolts for anchoring the walls to the foundation are placed while the concrete is still wet. With this lack of control joints, concrete will tend to crack wherever there are weak points such as: J-Bolt locations, wall abutments, corners, and locations where vertical rebar or conduit exist. Some other factors that can increase cracking are too much water in mixture, earthquakes, or improper batching at plant.
If concrete cracking is a guarantee, then how do we decide whether or not the cracks in our foundation are a structural threat? Not all cracking is a sign of trouble. Hairline cracks are usually hard to spot, but when they start to get larger then it is time to call a structural engineer or a foundation specialist. The engineer might recommend that the foundation have underpinning, a French drain installed, or have the crack injected with an epoxy. The information below is a summary of the injection process. Always consult a professional engineer if you are concerned about the structural integrity of your foundation and do not attempt to make the repair without the help of a professional.
Hairline cracks are generally not considered a structural threat by the engineer, but they should be sealed to prevent moisture from reaching the rebar. In general, larger Cracks 1/64" or greater usually require a structural epoxy injection.
In this picture you can see that the crack width is larger on top and gradually decreases towards the bottom. This is usually an indication of foundation settlement. This is a great example of when you need to call an engineer or a foundation specialist.
Cleaning the surface.
In order for the process to begin, the surface must be clean and smooth. this is achieved with a grinding wheel or a wire brush.
Surface is cleaned on both sides of the foundation wall and the full length of the crack.
Applying injection ports and surface epoxy
Once the crack has been cleaned, anchoring epoxy is used to mount the injection ports and seal the surface of the crack.
Anchoring epoxy is placed on both sides of the stem wall to prevent injection epoxy from leaking out. In this case, injection ports are placed on the exterior face of the foundation.
Injecting the crack with structural epoxy
Epoxy comes in two parts, when mixed a chemical reaction occurs causing the epoxy to cure and harden. Structural epoxy can be injected using a mechanical pump system or a dual cartridge caulk gun. With a mechanical system the epoxy is pumped at the proper ratio for both A and B parts to mix and activate. With a cartridge setup the epoxy is pumped through a mixer nozzle which starts the curing process. There are many different epoxies used for injections, but they all tend to be much stronger than the surrounding concrete. For most residential repairs I like to use Simpson Strong-Tie's "Crack-Pac" kit Crack-Pac® Injection Epoxy | Simpson Strong-Tie (strongtie.com)
With all injection ports in the open position, injection begins at the lowest port (Port #1). Once the crack is filled to where epoxy spills out Port #2, the bottom port is closed, we then begin pumping from Port #2. This process is repeated until the epoxy has filled the full length of the crack and begins to spill out the top of the wall.
In this photo you can see the black injection epoxy has filled the wall and begun to spill over. This is an indication that the crack has been completely filled with epoxy. After the curing process is complete, the injection ports and anchoring epoxy can be ground off for aesthetics if desired.
Epoxy can help bring back the integrity of the foundation. However, it is not a "fix all" for every situation. There are a number of reasons for foundation problems, and repairs should not be attempted without consulting a structural engineer or a foundation repair specialist. If you want to learn more about the injection process or types of epoxies than I recommend checking out Simpson Stong-Tie's website for more specific education content Search injection kits | Simpson Strong-Tie (strongtie.com)