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Step 1
Decide on the size of your concrete slab. You'll need to know the length and width so that you are able to calculate square footage of materials needed.
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Step 2
Calculate the amount of concrete you will need. Concrete is sold in cubic yards (27 square feet), so you will need to multiply your square footage from Step 1 by the depth of slab, then divide by 27. For example, a 10-foot-by-10-foot slab would require 1.3 yards of concrete. This is equal to [(10x10x.35 feet)/27]. The average concrete slab is 4 inches deep, but if you need more for your particular application, just calculate the depth you plan to use. Make sure to translate the thickness of the slab from inches to feet before using the equation above.
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Step 3
Contact local concrete distributors and ask for a price based one the amount you'll need. Add about 10 percent to the cubic yard figure you determined in Step 2, as some material will be lost during pouring and transport from the truck.
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Step 4
Ask the concrete companies about costs for delivery as well as overtime fees. These amounts are not typically included in the cubic foot pricing. Overtime fees are especially relevant, because concrete trucks work on extremely tight schedules. The operators expect you to be ready and waiting for them when they arrive, with easy access and no waiting around. They can and do begin charging overage fees if you delay the process in any way, and these fees can be significant.
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Step 5
Figure in the cost of excavation. A concrete slab is generally installed over a gravel base. The base is 4 inches, and the slab itself is 4 inches, with 2 inches above ground and 2 inches below. This means that for the average slab, you will be digging down 6 inches. If you are planning a particularly large or thick slab, you may need to consider renting a small excavator to help with this work. You can get rental prices from a local home improvement store or equipment yard.
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Step 6
Include the cost of gravel. For a 4-inch slab, you'll need the same amount of gravel as you calculated for concrete, as the gravel bed will also be 4 inches. You can get a price on gravel from a local home improvement store or quarry. Also include enough plastic vapor barrier to cover the gravel layer. This material is sold in rolls, and the cost is fairly negligible.
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Step 7
Add in the cost of tools if you don't already own them. You'll need a shovel, wheelbarrow, hoe or rake, trowels and four 2-by-4s to frame the edges of the slab. Because wet concrete can irritate the skin, you may also want to invest in some heavy-duty rubber gloves and/or boots.
