How to Attach a New Concrete Foundation Wall to an Existing Concrete Foundation Wall


To attach a new concrete wall to an existing wall, you'll need to secure rebar dowels inside the existing wall. Dowels are lengths of rebar that you'll place inside drilled holes and secure with a concrete epoxy product. There are several types of epoxy products that you can use for this purpose but they should be rated for concrete use to ensure proper installation. To complete the task, you'll need to tie the new foundation wall's rebar into the existing wall's rebar dowels.

Things You'll Need

  • Blueprints of new foundation wall
  • Tape measure
  • Chalk box
  • Level
  • Hammer drill
  • Masonry bit
  • Compressor or wire pipe brush
  • Masonry epoxy
  • Rebar dowels
  • Use a chalk box to snap vertical layout lines on the existing wall outlining where you'll attach the new foundation wall. Check that the layout lines are plumb using a level.

  • Read the plans for the new foundation wall to determine where you'll place horizontal rebar inside the new foundation wall. Use these measurements to place a pair of marks matching each horizontal course of rebar within the snapped layout lines; this will allow you to splice the new wall rebar with the dowels that will be protruding from the existing wall.

  • Attach a masonry bit that is a 1/4 inch larger than the rebar that you're using into the hammer drill. Drill holes using the marks you made for reference. Drill each hole one-half to three-quarters the thickness of the existing wall.

  • Slide the rotating bit in and out of the hole to clean out any debris. Clean the concrete dust out of the hole using compressed air or a wire pipe brush.

  • Fill each hole with concrete epoxy by placing the tip of the epoxy tube as deep inside each hole as possible. Place the rebar's butt end inside each epoxied hole and push it all the way inside. Allow the epoxy to set according to the manufacturer's recommendations before continuing to the new foundation wall.

Tips & Warnings

  • You can cut rebar dowels to length using a power saw outfitted with an abrasive cutting blade rated for metal cutting.
  • When using power tools on concrete, wear safety glasses and a dust mask to prevent injury.

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