How do I repair cracks in concrete?

expert EXPERT April 26, 2007

Here are the basic steps for repairing a crack in a concrete surface:

• With a hammer and a chisel, knock off all loose concrete.
• Hold the chisel at an angle and undercut the crack, so that the crack is narrower at the surface than it is below the surface. In other words, the crack will be wider at its base than it will be at the surface.
• Clean all dirt and debris out of the crack.
• Purchase a bonding agent or create one, by mixing equal parts of cement and sand with water to get the consistency of paint. Dampen the crack, and apply the bonding agent using a paintbrush.
• Mix one part Portland cement with three parts sand and add enough water to form a stiff paste like substance. Alternatively, purchase patching compound from your hardware store.
• With a trowel, fill the crack and smooth out the surface.
• Keep the patch damp for several days to allow it to cure.

There are a number of patching compounds (often epoxy based) they can be purchased. While they cost more, many do not require a bonding agent, and do not have to be kept damp while curing.