Caulking Concrete Cracks

How to make long-lasting caulk joints and keep water out

Seal cracks in concrete with durable urethane caulk. It'll keep water out and protect your foundation and walks from further cracking and eroding. You can do it in less than a half hour.

By the DIY experts of The Family Handyman Magazine

TIME

Instant!

COMPLEXITY

Moderate

COST

Under $20

How to caulk wide gaps

Cracks and gaps in concrete are more than just an eyesore. Water can get into the joints, freeze and then expand, making the cracks even larger. Gaps against a house can direct water against the foundation, leading to more problems. Once a year, go around your home and fill these gaps and joints with urethane caulk to prevent problems. The caulk is available at contractor supply stores, well-stocked home centers and hardware stores. For gaps and joints more than 1/4 in. wide, install foam backer rod to support the caulk. You want the rod to fit tight in the joint, so buy it one size larger than the gap.

A word of advice: Keep the urethane caulk off your bare hands and clothes; it's the stickiest stuff you'll ever touch. Wear disposable gloves when you're tooling the joints. If you get some on your skin, quickly wipe it off with a paint thinner–dampened cloth.

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How to caulk narrow gaps

Skip the backer rod and apply caulk directly to cracks narrower than 1/4-in.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Caulk gun

Spoon

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • Urethane caulk
  • Foam backer rod
  • Mineral spirits