How to Fill Existing Expansion Joints

Filling existing expansion joints assures a watertight seal.
Filling existing expansion joints assures a watertight seal. (Image: Jupiterimages/ Images)

Expansion joints reduce cracking in concrete walls, floors and driveways. Concrete expands and contracts with temperature fluctuations and water absorption. The expansion joints absorb the movement that causes cracking Expansion joints are commonly filled with caulking to avoid water penetration. However, this caulking breaks down over time with exposure to the weather.

Things You'll Need

  • Utility knife
  • Caulking gun
  • Long nail
  • Polyurethane caulking
  • Polyurethane foam rod

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Remove the old caulking from the expansion joint by cutting along the seam between the caulking and the concrete. Scrape out the old material and clean all remnants from the joint.

If the joint is more than 1/4 inch wide, push a polyurethane foam rod into the joint so that it provides a backing for the new caulk. If the joint is tighter than 1/4 inch, a rod is not necessary.

Insert a tube of caulk into the caulking gun. Cut the tip off of the cartridge with the utility knife so the hole is less than 1/4-inch wide. Poke a hole in the tube by pushing a long nail or thin rod down the applicator.

Apply caulking evenly into the joint, filling the space completely. Pull evenly on the trigger on the caulking gun.

When dry, cut away any excess with utility knife.

Tips & Warnings

  • To caulk a clean line along the joint, apply painter's tape on either side of the joint.
  • If original caulk is oil based, you should clean out the old material with alcohol.


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