Concrete Ideas, pt. 3

Before your concrete arrives, you need to have the site ready to pour. This means site preparation and setting up forms. This part of the concrete project should be finished at least the day before the concrete comes. You want to have everything ready for the arrival of the concrete.

Site Preparation
All site prep involves excavating of some sort. Footings need a trench, while slabs need to have enough soil removed for the sand or gravel base plus and concrete that will be below ground level.

To prevent the soil from settling under the concrete, it must be poured on undisturbed soil. If you dig too deep, you will either have to add more sand or gravel (packed down firm) or more concrete. In warmer areas with firm soil, where freezing is not a problem, the concrete can be poured directly on the prepared soil unless the building code calls for a sand or gravel base.

Forms
When pouring footings, setting up forms can be as easy as making sure the soil is stable. If it is, you can use the trench itself for a form. Otherwise you will need to build forms to keep the concrete where you want it.

To support a wall, continuous footings need to be 6 to 12 inches thick. The forms are built from either 2x6 or 2x12 lumber. The forms for 6 inch footings are supported by stakes about every 3 feet, while 12 inch footings are staked every 2 feet. This helps support the forms so that the wet concrete does not push the forms out of shape.

The forms for a slab can be made from 2x4s with stakes every 4 feet. If you are pouring a large slab, such as a driveway, you will need to place expansion material every 10 feet or so to help prevent the slab from cracking when it expands and contracts with the weather.

Reinforcement
Concrete needs to be reinforced to help it support the weight placed on it and to help it survive the changes in the weather. Footing usually contain two steel reinforcing bars, or rebar, laid the lenght of the footing. When you need to use more that one piece to run the lenght of the footing, overlap the rebar by 15 to 20 inches (or what is called for in your local building code.) When placing rebar in the corners of footings, bend the rebar around the corner rather than having the rebar meet at the corner. This helps provide a strong, stable corner. Check with yolur local building code to see how much concrete must cover the rebar in footings. Usually this is about 3 inches, which means that you need to support the rebar to keep it 3 inches below the top of your form.

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