How to seal expansion joints in concrete

Written by kenneth crawford
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How to seal expansion joints in concrete
(Jupiterimages/ Images)

Concrete driveways seldom consist of one long piece of concrete. Rather, they are several slabs of concrete separated by gaps known as expansion joints. Expansion joints allow the concrete slabs to expand and contract with the temperature without causing stress cracks. These joints require sealing to prevent water from getting in the joint and under the slabs. Sealing expansion joints in concrete requires a sealant that combines a base sealing component with a curing ingredient. All materials necessary for sealing expansion joints are available at home improvement centres.

Skill level:

Things you need

  • Steel wire brush
  • Broom
  • Wet/dry shop vacuum
  • Tape measure
  • Backer rod
  • Utility knife
  • Concrete epoxy sealant
  • Paint stick
  • Plastic putty knife

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  1. 1

    Clean the inside of the expansion joint thoroughly. Briskly brush the joint with a steel wire brush to remove any loose concrete. Sweep the length of the joint with a stiff broom, ensuring that you get the loose debris from between the two slabs. If possible, vacuum the expansion joint with a wet/dry shop vacuum.

  2. 2

    Measure the length of the joint with a tape measure and transfer the measurement to your backer rod. A backer rod is made from flexible material that is water resistant. Cut the backer rod to the measurement with a utility knife.

  3. 3

    Insert the backer rod into the expansion joint. Press the rod down with your fingers to ensure the rod rests in the bottom of the joint.

  4. 4

    Open the concrete epoxy sealant and mix well with a paint stick. Pour the sealant into the expansion joint on top of the backer rod until it is 1/16-inch below the concrete surface. Smooth out the sealant with the plastic putty knife. Allow at least 30 minutes for the sealant to cure.

Tips and warnings

  • Concrete joint and crack sealant is available in cans and tube form. You can use the tube type in a caulking gun if the expansion joint is less than 1/4 inch wide.
  • Read the directions on the sealant product you purchase for specifics of that brand of sealer.

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