Q.: We do everything possible to prevent cracking of the concrete driveways and patios that we place. We promptly cut joints to the correct depth and space them no more than 12 feet apart. We also use medium-slump concrete and start curing it as soon as we can without marring the surface. However, we still get an occasional crack, and the homeowner often wants us to repair the crack or remove and replace the cracked panel. Is there any information we can give homeowners to reassure them that a crack won't affect the structural function of their driveway or patio?

A.: Let's start with the most common remedial requests from homeowners. Trying to repair a driveway crack by injection or patching usually makes the crack look worse than it did before the repair. And if you replace a panel, you'll almost never match the color of the surrounding concrete. So both of those fixes are likely to be objectionable from a cosmetic standpoint.

The effect of cracking on the structural performance of a driveway depends on crack width. Load transfer by aggregate interlock becomes ineffective when crack widths exceed about 0.04 inch. Thus, if the crack width is less than 0.04 inch (about the diameter of a standard paper-clip wire) the driveway can still provide adequate load transfer across the crack. An easily used clear-plastic crack-width gauge enables you to measure width at several locations along the crack so you can calculate an average crack width. You can get this free gauge by calling Construction Technology Laboratories Inc., Skokie, Ill., at 847-965-7500 and leaving your name and address.

We suggest showing owners photos of driveways with repaired cracks or replaced panels to illustrate the cosmetic problems associated with both of these approaches. Then, if you can demonstrate that the crack isn't wide enough to affect driveway performance, you can make a strong case for the use-as-is solution.