How To Prepare the Garage Floor

How To Prepare the Garage Floor

How To Prepare the Garage Floor

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Garage walls are either framed directly on the slab or on a 6- to 10-inch curb around the perimeter. If your walls sit on a curb, you need to extend that curb through the opening. The curb helps keep water out and it also protects the wood framing from moisture damage. You should be able to determine whether or not you have a curb by examining the sides of the garage opening after removing the jambs.

Difficulty: Hard

Time Required: Several days

Here’s How:

  1. Before you begin, inspect the condition of the concrete slab in the garage. If it is badly damaged, make the the necessary repairs before proceeding. If you aren’t sure how to make that determination, seek the advice of a construction professional.
  2. The first step in extending a concrete curb is to insert some reinforcing bars (rebar) into the sides of the existing curb. This will help tie the new and old sections together. With a hammer drill, which you should be able to rent (if not borrow) and a 1/2-inch masonry bit, drill two holes about 6 inches deep into each curb. The holes should be centered, one on top of the other. Tap 12-inch pieces of rebar into each hole with a small sledgehammer or large hammer.
  3. Build a form for the concrete with two pieces of lumber cut to match the height of the curb. Use 2x lumber that is about 3 or 4 feet longer than the opening. Prop the boards in the opening, using concrete blocks or other heavy objects to hold them in place. For added security, you can temporarily bolt the boards to the existing curb or nail several small boards across the tops. You will be pouring concrete between these big boards and you want to make sure they don’t move when you do.
  4. Make sure that you have enough concrete on hand before you begin. Calculate the cubic feet you will need, then buy as many bags as necessary.

Mix bags of ready-mix concrete with water in a wheelbarrow or large tub. Shovel concrete into the form. Add small amounts at a time and try to avoid hitting the boards. Once the form is filled, use a mortar trowel to smooth the tops.

  • While the concrete is still wet, insert 1/2-inch anchor bolts in the center spaced no more than 6 feet apart and 12 inches from each end. Plan ahead so that you don’t set anchor bolts where wall studs will be located. Let the concrete cure for three or four days before removing the form boards.
  • Most garage floors slope toward the door or a drain. You can level the floor if necessary using a self-leveling concrete or gypsum-concrete mixture. Check with your supplier or the manufacturer to make sure you choose a product suitable for the depth you require. If you are not extending the curb, check with a construction professional before trying to level the floor.

    Follow the manufacturer’s instructions carefully. These compounds seek their own level, so you only need to mix and pour them. Wait at least two days before walking on the surface and a week or more before installing any floor covering.

    What You Need:

    • 1/2-inch rebar
    • Hammer drill, with 1/2-inch masonry bit
    • Small sledgehammer
    • 2x lumber for concrete form
    • Concrete blocks
    • Ready-mix concrete
    • Wheelbarrow or mortar tub
    • Shovel
    • Mortar trowel
    • Self-leveling concrete or gypsum-concrete mixture


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