How to Repair a Water Leak on the Floor of a Sunken Concrete Wall

Clean the wall and floor with a pH-neutral cleanser and a nylon scrub brush. Remove any oil from the two surfaces with a concrete degreaser and the brush. Rinse off all cleaners with clean water.

Dry off the concrete with rags. Measure the width of the crack with a tape measure to determine the nature of the repair required. For narrow cracks of 1/4-inch width or less, a urethane caulk repair will be sufficient, while wider cracks require a foam backer rod and caulk repair.

Put on a pair of rubber gloves to protect your hands from the repair materials. Cut the tip off a tube of urethane caulk with a utility knife. Place the tube of caulk into a caulking gun and push the locking mechanism on the rear of the gun against the base of the tube to hold it in place.

Hold the tip of the caulk tube against the end of a crack in the concrete narrower than 1/4 inch. A sunken wall will leave a crack or gap where it has broken from the surface of the floor and water can seep in. Press the trigger of the caulking gun to dispense the caulk into the crack. Follow the length of the crack with the tip, filling the narrow crack with the urethane caulk. Draw your finger along the line of caulk to smooth it out along the surface of the crack.

Cut a strip of foam backer rod the length of the wall using a utility knife for a crack that is wider than 1/4 inch. Stuff the rod into the joint along the floor between the floor and the wall, leaving a 1/4-inch space above the rod clear. Use your fingers or a putty knife to push the rod into position.

Cut a tip of the tube of caulk with the utility knife at an angle to create an opening the same size as the large crack. Fill the 1/4 inch of space above the backer rod with the urethane caulk. Smooth the caulk with the rear of a metal spoon. Clear any caulk sticking to the rear of the spoon away with a piece of cloth dampened with mineral spirits. Allow the caulk to dry overnight.

Check the wall daily for the next three to five days for signs of leakage. If leakage occurs, examine the floor for the location of the leak. Repeat the repair process on the affected area.

Pour concrete sealer into a hand-held pump sprayer. Work the pump on the sprayer two or three times to prime the unit, and then point the nozzle of the sprayer at the floor from a distance of about 3-feet. Spray the floor with the sealant, covering it with enough of the sealant to create a slightly wet look.

Roll the sealant along the floor with a low-nap paint roller to spread it evenly in place. Allow the sealant 48 hours drying time before stepping onto the floor area.