Q: We bought our house in 1980, and it was built in 1939. I don’t know how old our concrete driveway is, but it has many cracks that weeds are growing from. Over the years the cracks have gradually gotten bigger. Money is tight and we would rather not have to replace the entire driveway. Is there a way to repair those cracks? I’m not looking for a perfect solution. Any advice you can give will be most appreciated.
A: No need to replace the driveway. Patching the cracks will slow down the deterioration and give your driveway many more years of useful life.
The main reason for fixing concrete cracks, aside from looks, is to help keep moisture from leaching into the soil causing expansion and contraction that further damages the concrete.
Before you begin the repair, scope out the general area and try to get a feel for what caused the crack. Tree roots and standing water are two common causes. Before you begin fixing the actual crack, try to identify and eliminate the source. That could mean cutting out an offending tree root or filling a depression in the concrete.
Regardless of the size of the crack, job one is preparation. It’s critical to clean and perhaps widen the crack to create clean surfaces that are ready to bond with the repair material you choose. You’ve got weeds, so first use a herbicide to kill them — "roots and all" as one popular brand says. Spray the weeds and give them a week or so to die.
Begin preparing the crack by breaking off any loose pieces of concrete with a cold chisel. The goal is to get a solid surface to bind to the patching material.
After the chiseling is done, use a wire brush to loosen any remaining debris.
Remove as much loose debris from the crack as possible. The gold standard is to use an air compressor, but if you don’t have one available, use a shop vac to vacuum out the crack. Your goal is to clean out all of the dust and chips.
Fixing cracks less than 1/2 inch
Textured caulk, concrete sealer or pourable concrete grout are options for repairing small cracks. Choose a product that is flexible. It should give a little with earth movement. Read the labels and ask the salesperson at the home center for recommendations.
Whichever product you choose, be sure to follow the manufacturer’s instructions. Completely fill the crack and use a pointing trowel or your thumb to push the grout or sealer into the crack.
Fixing larger concrete cracks
For cracks wider than 1/2 inch, use a cold chisel to undercut the crack to make sure that the crack is wider below the surface than at the surface. This will keep the patching material from popping out of the crack as the concrete expands and contracts.
If using pourable concrete grout, apply it in 1/4-inch increments. Another alternative is to partially fill the crack with damp sand leaving 1/2 inch to the surface of the crack to be filled with the grout. Either way, multiple applications are required to allow for proper drying and shrinkage. Overfill the final coat to compensate for the slight shrinkage the grout will experience as it dries.
If using vinyl concrete patch, mix only as much as you can use within the pot life of the product, usually less than 20 minutes. Begin by wetting the crack with a spray bottle or hose. Spread the patch material into the crack forcing it into the crack with a pointing trowel or your finger. Again, fill the crack in layers no thicker than 1/4 inch to account for shrinkage. Again, damp sand can be used to raise the depth of the crack to 1/2 inch.
If using textured caulk, it has to be applied to a dry surface. If the crack you’re repairing is deeper than 3/8 inch, fill the crack with sand or foam backer board. Cut off the tip of the applicator to a size that matches your crack, not exceeding 1/4 inch (refer to the caulk manufacturer’s guidelines). In addition to completely filling the crack, apply some overfill to account for shrinkage as the caulk dries.
When finishing each of these options blend the final patch material with the surrounding concrete to form a good seal of the crack. A small brush, a broom or even a block of wood rubbed across the patch will do the trick.