Concrete Crack Repair

Summary: If you need to do concrete crack repair for your driveway, sidewalk, or concrete garage floor, injecting the crack with a two-component polymer is often the easiest way to repair cracks in concrete, plus cleanup is minimal.

Proper concrete crack repair methods vary according to what the concrete is used for.

The answer to whether a crack in concrete is problematic may also be in the eye of the beholder. The owner or engineer may think it's fine, but the architect may find it unacceptable.

It will also depend on what the crack is typically exposed to.

For reinforced concrete in a dry environment, a crack greater than 0.016 inches in width needs repair.

If the crack is in a moist, humid environment, the maximum tolerable crack width is less: 0.012 inches in width.

If de-icing chemicals are used on the concrete, then cracks larger than 0.007 inches in width should be repaired.

Cracks in the presence of seawater or seawater spray should be fixed if they are greater than 0.004 inches in width.

With regular, non-reinforced concrete, the guidelines are more preferential in nature.

These guidelines shouldn't be used to judge the widths of cracks in lightly reinforced slabs or unreinforced basement walls.

Even in reinforced concrete, the occasional, isolated crack width greater than the guidelines may not be cause for an emergency repair.

Keep in mind that the crack width you can observe is not necessarily an indicator of the structure's durability, or lack thereof. Here are the tools and materials you will need for polymer injection repair:

A dual-cartridge dispenser that uses cartridges is a budget friendly and simple tool for injecting repair polymers into concrete cracks.

This dispenser also requires minimal maintenance and virtually no cleanup.

You can discard used up dispenser cartridges or reseal partially full ones still ready for your next job.

A spring-loaded dispenser gives you total control of the injection pressure to keep it in the 30 psi range, which is best for filling in cracks.

If you're fixing a fairly large crack, consider inserting hardened nails into it. Or, you could drill a half-inch diameter hole and pound in a small piece of reinforcing steel into the hole to help hold the repair in place.

Make sure that any nails or pieces of steel are sunk at least half an inch below the top of the patch.

For fairly large cracks, you need a chisel and hammer to undercut the crack before filling it in.

You'll also need a finishing tool, such as a steel trowel or a magnesium or wood float. Like many repair jobs, the prep work is at least half the battle when making concrete crack repairs.

Sweep or brush away any loose concrete and dirt from the crack.

The main thing you can do that will help this repair last is to undercut the crack. This involves using a chisel to enlarge the deepest part of the crack along the entire length of the crack.

You tap the chisel in at an angle with your hammer until you make the crack wider at the bottom than at the top.

Undercut the crack to at least a 1-inch depth. You don't want a V-shaped crack because the repair compound will expand its way right out of the crack. The actual concrete crack repair process is pretty straightforward.

Using your low pressure injection dispenser, slowly fill in the crack at low pressure between any nails or reinforcing steel you've installed.

Use your trowel to finish and smooth the repaired area.

It is sometimes best to wait a few minutes for the compound to stiffen a bit before smoothing.

When you're done, cover your repair with a piece of plastic weighted down at the edges so it won't blow away and so air won't get underneath the plastic.

Leave the plastic in place for three to four days before removing it.

If you have the right tools and do solid prep work, you can make many concrete crack repairs on your own.

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