How to Repair Cracks in Cement Block Walls

Put on a pair of safety glasses and a dust mask. Avoid getting the dust from the cement blocks in your eyes or lungs.

Clean out the edges and inside of the crack. Scrape along the inner edges and inside the crack with a small wire brush. Remove any jagged edges or irregularities.

Remove any of the dust by blowing into the crack. If you have access to an air compressor, use it to blast the dust out of the crack. Vacuum around the edges of the crack to remove any dust stuck to the wall.

Use a small masonry chisel to undercut the crack. Place the edge of the chisel along the bottom edges of the crack and tap them gently with a hammer until you break through the cement. Carefully expand the bottom of the crack so that it is wider than the top, much like a dovetail joint. This will provide the cement epoxy with a place to drain and expand, so it does not push itself out of the crack as it dries.

Place the nozzle of a tube of cement/concrete epoxy at the top of the crack. Squeeze the tube of epoxy as you guide it down the length of the crack. You do not need to completely fill in the crack you chiseled earlier; some of the epoxy will drain down into it on its own.

Spread the epoxy evenly with the edge of a putty knife. Wipe any excess away from the cement block with a clean rag. Allow to dry.

Check the cement epoxy after it dries. Squirt small drops of epoxy into any gaps or spots that are not flush with the surface of the cement block. Allow to dry.