Greve suggests allowing the concrete to cure for at least a month or two. “Then if you find that this problem does occur, the joint may be fixed with dowels. This should be considered a permanent solution.”

Epoxy fillers

Semi-rigid joint fillers used for industrial applications are not elastomeric sealants, says Bill Phelan, senior vice president with Euclid Chemical Corporation. “A true sealant has elastomeric properties, meaning that it moves,” says Phelan. “It has no benefit to a joint in an industrial setting where you have small, hard-wheeled traffic. Cars and trucks with big pneumatic tires are fine with such sealants though.”

Phelan feels the biggest problem with joint filling is being sure that the semi-rigid joint filler—either an epoxy or a polyurea—is installed flush with the slab, not concave as a typical sealant would be. The reason for this is that the edges must not be left open. Often such sealants are not installed flush, and the small wheels damage the edges. “Most of the people install the semi-rigid joint fillers early,” says Phelan. “If a rigid material that bonds really well is used, such as a typical epoxy, then the joint is inactive, and the slab will subsequently crack. The joint is not working.”

Phelan identifies a number of different types of concrete slab cracks. Here are a few of the more common ones and how they may be dealt with.

A. Wide crack—offset

For this type of crack, the slab on one side is raised more than ¼ inch and the crack's width will be greater than ¼ inch. To repair:

  1. Plane the high side even with an abrader or terrazzo grinder.
  2. Remove the loose, cracked concrete down to solid concrete.
  3. Prime the side of the crack with epoxy adhesive.
  4. Fill with epoxy joint filler.
  5. Seal abraded concrete with epoxy sealer.