Another method of foundation crack repair is crack injection. This can typically be done on all sizes and types of cracks, with different materials being used for structural versus solely leak repair.
When preparing for a foundation wall crack injection, a mastic/epoxy is used to adhere the ports to the wall as well as to seal off the interior side of the crack. Once the mastic sets, the crack repair material is pumped into the crack to fill the void. Two of the most common crack injection materials are polyurethane and epoxy.
Polyurethane is more flexible and can even allow for the repair of weeping cracks, in some circumstances. Polyurethane products dispense with a very low viscosity initially (like water), and typically foam and expand many of times over before hardening in the crack. However, polyurethane is not structural. If a structural repair is necessary, then an epoxy injection product must be used.
Epoxy is as strong as concrete and forms a structural seal. However, epoxy hardens much more slowly than polyurethane, making it prone to leakage out of the crack on the outside of the wall if a void is present. Epoxy is also difficult to work into a thinner crack because it is more viscous than polyurethane.
*It should be noted that these methods can only be used on poured concrete wall, not concrete block walls.
Also, a word of caution: one of the main reasons a crack cannot be injected is when a homeowner or novice tries to repair the crack him/herself by slathering on hydraulic cement or a similar product. This often makes it nearly impossible to locate and prep smaller cracks for the injection method. So again - leave it be and have a professional look at it first! You could very well be doing more harm than good and costing yourself money.