How to Repair Brittle Concrete Cracks

If your house is more than a few years old, chances are the concrete has moved, settled or cracked. Here are answers to the most common problems:

Bricks of the Exterior

Concrete is very brittle, so the slightest movement of the underlying soil will create a crack. Control joints — the grooves intentionally furrowed into the surface — are meant to absorb this movement, so the cracks will follow those straight lines and look less random. As those cracks open, fill them with a good epoxy-based crack filler. Many come in a caulking tube, but the most convenient versions are a pour-in liquid. They are a little more expensive but incredibly convenient. For really deep cracks, fill the spaces with fine sand nearly to the top and then apply the filler.

One special case is that pesky gap between the garage floor and the driveway. It’s usually too wide and deep to caulk. You can insert a redwood board edgeways into the gap — although it probably will require some adjustment with a table saw or power sander. Once it is driven into the crack, you can use some conventional epoxy-based sealant along the edges.

Another product, Slab Gasket, is a gray, vinyl, weather stripping-like product that comes in various widths and heights. Measure the dimensions of your gap, then go toslabgasket.com to check out this clever, homeowner-friendly invention.

Surfaces such as stoops, patios and driveways, which actually sink and tip, are another matter. If they slant into the foundation — letting water run toward the structure — or, if they’ve broken apart causing a “toe stubber” effect, it’s time for more serious action.

They can be pushed back into place by a process called mud jacking. A high pressure grout (soupy concrete, dirt, sand and water) is pumped under high pressure through small holes drilled in the surface. It lifts the slab back to its original position, and the hardened grout underneath then becomes a stabilizing “footer” under the whole thing. It’s a little pricey but usually much cheaper than a complete tear-out and replacement.

Driveway surfaces that have deteriorated from freezing, poor drainage or the application of salt are really difficult. It’s called spalling, and the result is a surface that has a “cottage cheese” look. Skim coating with new material usually doesn’t work long-term. The best answer is to tear it out and replace it with new concrete — after re-stabilizing the soil base and fixing the drainage.

Bricks of the Interior

Settling around the perimeter of interior concrete slabs is quite common. Areas that are permanently exposed, such as your garage, also can be mud jacked. The next most common site is a carpeted family room or bedrooms on the ground level of, say, a tri-level home. Rather than suffer the disruption and mess of mud jacking, simply roll back the carpet and apply a skim coat of a floor-patching material or concrete mortar mix along the edges to level the area.

Finally, the big enemy of concrete slabs — whether inside or out — is surface water. Make sure that patios, walks and drives drain quickly and that water can’t seep under them from nearby downspouts. Also, keep the snow and ice off to avoid the winter freeze/thaw cycle.