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Pour a Concrete Floor

Flooring Installation, Floors, Stone and Concrete November 2, 2009 Sonia

A uniform grade is then established using fine gravel 1 to 2 inches deep. The best choice in gravel is called base rock. This has gravel and fine particles that pack down smooth. Once the gravel is in place, tamp it down smoothly.

If the pour is large you will need to divide it into smaller, easily worked sections using interior forms held in place with stakes. Pour one area, remove the forms and stakes and pour the second or third areas.

Floors should be reinforced according to local regulations. In the case shown, wire was used as reinforcement. Rebar may be used for slabs requiring more support. Garage floors are usually poured 4 to 6 inches thick.

All supply and waste lines are stubbed, the subsurface prepared, gravel and a vapor barrier installed, and the slab poured.


You must also install all waste and supply lines for bathrooms, kitchens and so forth, leaving stub pipes. Close these pipes off to make sure nothing gets into them until you’re ready to connect them. In many instances you will also wish to install a plastic vapor barrier over the gravel.

Determining the Amount Needed

Concrete for a slab or floor is commonly ready-mixed and delivered in large trucks, although you can mix your own for very small jobs. Ready-mix concrete is sold by the cubic yard. To order the correct amount, tell the concrete supplier the width, length and thickness of the slab or floor you intend to pour. They will calculate the quantity needed, and in most instances supply slightly more than needed. You should have a place to dump a small amount of leftover concrete. They will normally add 5 to 10 percent for losses due to uneven subgrade, spillage and so forth. 

Begin the pour in the back corner of an in-foundation pour. As the liquid material is poured, use rakes to pull the material toward the building opening or door.

Making the Pour

Concrete should not be poured on extremely hot, dry days as the material will dry out before it can cure properly. Concrete should also not be overworked. If the pour is overworked, too much water will be floated to the surface, which can cause scaling after the concrete dries. The material should be spread evenly and quickly once the pour begins, slightly overfilling the forms.

Pouring a floor—even a small floor—takes manpower. Pour when your best buddies are available and equip them with rubber boots, safety glasses and rakes. Once the pour has started, the liquid material should be evenly spread over the area using the rakes. Make sure all corners are filled. Leave the concrete slightly higher than the top edges of the form boards.

Use a screed board to level the concrete between the forms or guide boards.

The next step is to use a screed board to drag off the excess concrete. The screed board is rested on the form boards and must extend past the form edges at least 3 inches on each side. Screeding is a two-man operation and at best is hard work on a large pour. Beginning on one end of the pour, place the screed board over the form boards with a person on each end of the board. Using a side-to-side motion, and at the same time pulling the board, sweep it across the form boards to the opposite end. Screeding levels the concrete with the tops of the form boards, pulling off excess concrete. Any low spots will be visible and should be immediately filled and the area rescreeded. A jitterbug or tamper should be used to settle the concrete and remove air pockets around the edges.

In standard construction, anchor bolts are needed to anchor the walls to the slab. These can be placed in holders nailed to the form edge, or pushed in place as the pour is made. The first method is more precise. The anchor bolts must always fall between the stud locations. If you locate one under a stud, you’ve got problems.