Basement walls withstand a lot of stress for a variety of reasons. Hydrostatic pressure is the force of the water in the soil surrounding the foundation constantly pushing against the structure. Freeze and thaw patterns in colder climates also cause outside pressure on the walls. As the ground freezes, it expands and presses against the foundation. As concrete cures, it shrinks, causing basement walls to crack. Vertical cracks generally are not a concern. Horizontal cracks can result in structural failure. If you have a horizontal crack, consult a structural engineer before attempting a repair.
Polyurethane Foam--Leaking Crack
Chip away loose pieces from the edges of the crack with a masonry cold chisel and a hammer. Use a wire brush to brush out small bits of debris. Vacuum the crack to remove masonry dust.
Insert the tip of the applicator bottle of polyurethane foam sealant into the crack and inject the foam into the crack, filling up the spaces inside the crack. Some brands of polyurethane foam sealant require the use of a plastic injector, which is usually part of a crack repair kit. When the polyurethane foam encounters the water or moisture, it will react and expand, filling the crack.
Apply a layer of an epoxy-based sealant over the crack with a putty knife or apply a bead from a caulking gun. Smooth the surface of the sealant with a putty knife from the crack out 2 to 3 inches. Make the edges of the sealant thinner and thinner as you move away from the crack. If you have a crack sealer kit, the epoxy-based sealant is part of the kit.
Hydraulic Cement--Wet Crack
Chip away loose concrete with a masonry cold chisel and hammer from the inside edges of the crack. Brush out small loose bits of concrete or mortar with a wire brush. Sweep out the crack with a small whisk broom or vacuum dust out of the crack.
Press hydraulic cement into the crack with a trowel or putty knife, forcing it in as far as possible. Continue to apply hydraulic cement to the crack, layering it on until you reach the surface height of the wall.
Apply a thin coat of hydraulic cement over the repair and 2 to 3 inches past the crack. Feather the edges of the hydraulic cement as you move away from the crack.
Elastomeric Joint Sealant--Wet or Dry Cracks
Place a tube of elastomeric joint sealant into a caulking gun.
Place the tip of the tube into the crack and squeeze the trigger to run a bead of sealant into the crack. If the crack is too narrow for the tip of the tube, run a bead over the crack.
Run a finger over the bead of sealant to press it into the crack and smooth the surface.