How to Install a Concrete Garage Floor

A concrete floor provides a solid foundation for a garage.

Putting a concrete garage floor in a garage as you build it is the easiest way to have a solid garage foundation. It's not an easy task to pour concrete flooring for a garage. Pouring the floor takes a lot of preparation and labor. If you have some experience with pouring concrete on a smaller scale, you may want to take this project on. Otherwise, consider hiring a professional to build your garage foundation.

Things You'll Need

• String
• Stakes
• Measuring tape
• Shovel
• 2-by-6-inch lumber
• Builder's square
• Laser level
• Small gravel
• Skid steer loader
• Pre-mix concrete
• Rebar
• Wire mesh
• Wire ties
• Rake
• 2-by-4-inch lumber
• Tamper
• Bull float with extension handles
• Edger
• Trowel
• Broom

Instructions

1. Tie string to stakes to mark where you plan to install the garage floor. Measure the length and width you plan to build. Allow 4 inches extra for the width of the garage and 6 inches extra for the length. This gives you room to add the anchor bolts that hold the walls in place. Adjust the string and stakes as necessary to ensure each of the four corners is absolutely square.

2. Dig out the dirt for the footings around the perimeter of the pour, using a shovel. The footings need to be at least 12 inches deep and 16 inches wide to meet most building codes.

3. Remove rocks and other debris in the way inside the perimeter of the garage. Dig it out with a shovel by hand or use the front-end loader on a skid steer loader to complete this task. Remove the top layer of soil with the equipment as necessary to level this inner area. Allow for the concrete flooring to be at least 4 inches thick for automobiles and 6 inches for heavier vehicles. Use a laser level to help ensure the area is level.

4. Build the forms for the garage foundation out of 2-by-6-inch lumber set on its edge. Using your string guide, place long edges of two boards vertically side-by-side in the outer perimeter of the footing trench. Use stakes placed around the outside of the forms to anchor the lumber in place. Use a builder's square to verify that the corners remain square. Use a laser level to ensure the tops of the forms are level.

5. Cover the inside area of the garage slab with a layer of small gravel. Set any drains or pipes for plumbing at this time.

6. Set the wire mesh reinforcement material in place in the flat center area. Use wire ties to hold it in position.

7. Pour the footings for the concrete. As the concrete goes into the footing trench add reinforcement bar, or rebar, on two levels. Continue to pour the rest of the concrete in the middle of the garage floor. Use a rake to work the concrete into corners.

8. Set a long piece of used 2-by-4-inch lumber on top of the wooden form. Use it as a screed to level the concrete on the garage floor. With a partner, work the board back and forth across the concrete pour to work off the excess concrete. Work more concrete into areas that are too low.

9. Tamp around the edges of the concrete to remove air pockets that develop there.

10. Set anchor bolts vertically into the perimeter of the foundation. Place them so that their location does not coincide with the spacing of wall studs, which is typically 16 inches on center.

11. Push the bull float away from you at an angle to level the concrete surface even more. Pull it back toward you to smooth the surface. The extension handle allows you to reach the center of the pour. Continue doing this across the entire cement floor.

12. Separate the concrete from the forms, using an edger. This tool creates a slightly rounded edge that is less likely to break.

13. Trowel the surface when a footprint leaves less than a 1/4-inch impression. Use your arms to make wide arcs with the trowel. Cover the surface several times to create a smooth surface. On the last pass, use a broom to create a slightly rough surface if you prefer.

Tips & Warnings

• Contact your local building codes administrator before beginning this project to acquire necessary building permits.

• Order the concrete pre-mix from a local supplier. Have your garage floor dimensions ready when you call so you can order the right amount of cubic yards of concrete.

• Rebar and wire mesh help prevent concrete from cracking as it freezes and thaws.

• Have everything ready to go when the concrete truck arrives. If possible, have several people there to help you level and trowel the concrete.

• Allow the concrete to dry slowly for at least a week. If the weather is hot and dry, you may have to dampen the concrete, or put a piece of plastic over it to keep it from drying too fast. Once the concrete is dry, you can remove the forms and continue building your garage.

• Clean all tools with water before the concrete has a chance to set up.

References

• Absolute Garages: Concrete Requirements
• Extreme How-to: Pour a Concrete Floor