How to Cut a Trench in a Concrete Garage Floor

Written by jim wildman
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How to Cut a Trench in a Concrete Garage Floor
(sledgehammer breaking the concrete image by timur1970 from

Home repair and maintenance is an ongoing process when you own a home. One item in home repair is site drainage. If the builder did not supervise the concrete subcontractor, your garage and driveway may not drain properly. This is just one scenario that may require the property owner to trench the garage in order to add a drain along the door. The average do-it-yourself handyman can trench the garage's concrete with just a few tools.

Skill level:

Things you need

  • Tape measure
  • Pencil
  • Chalk line
  • Cut-off concrete saw with diamond blade (available at a tool rental store)
  • 4-inch grinder with diamond blade (available at a tool rental store)
  • Sledge hammer
  • Safety glasses
  • Dust mask
  • Hearing protection

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  1. 1

    Verify that the garage is not a post-tension slab. A post-tension slab has steel cables within the concrete. After the concrete pour, when the concrete has dried awhile, a machine pulls the steel cables extremely tight. This keeps the concrete under constant tension. If you cut through one of these cables and release the tension, the cable can snap through the concrete and amputate limbs. Check with the builder if possible. Look, if you can, at the outside edge of the concrete on two adjacent sides. If you see a row of black circles about 16 inches apart along one of the edges at the level of the interior slab, this would indicate a post-tension slab.

  2. 2

    Mark the garage floor at both ends where you need to trench the concrete. If adding a continuous drain, verify the width required so that the drain will be a perfect fit.

  3. 3

    Snap a chalk line between the two marks to indicate one side of the trench. Repeat for the other side of the trench.

  4. 4

    Put on your safety gear, to include safety glasses, hearing protection, dust mask and trousers.

  5. 5

    Score the concrete using a cut-off concrete saw. Place a 1x6 straight piece of wood against the snapped line. This will act as a guide to score the concrete about 1/4-inch deep. The concrete in a garage is between three and four inches thick in most cases. Cut all the way through the concrete following the 1/4-inch scribe line. This will make it easy to make a straight cut. You will have to over-cut the edges to cut all the way through the concrete. You can use a 4-inch grinder with a diamond blade to cut in confined spaces.

  6. 6

    Strike the concrete between the cut lines with a sledge hammer. This will break the concrete so you can remove it.

Tips and warnings

  • Wear safety equipment when cutting concrete.

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