If the other side of the wall is accessible, see if the crack goes clean through. If it does, seal it up with crack sealer, too. Allow the sealer to cure for 6 to 10 hours before injecting the epoxy. Thoroughly mix the LCR epoxy using the plunger rod that comes with the kit. Place the LCR cartridge into a caulk gun. Starting at the lowest injection port, dispense the epoxy into the crack. Continue squeezing the trigger until epoxy begins to ooze out of the port directly above.