Pouring a concrete slab is not rocket science, but you need to know what you're doing. A poorly installed concrete slab will crack and break well before its time. By following these tried and true methods, you can be sure that your project will be safe and last a lifetime. The average do-it-yourself homeowner can pour his own concrete slab in 1 to 2 days, depending on the size of the project.
You'll want to pour the concrete slab on level, packed dirt. You should never pour a slab on top soil or other loose lying soil, which will settle and cause the slab to crack. Remove the top soil and add crushed gravel. Do not use sand as a compacting base. Dig down at least 3 1/2 inches--the thickness of a standard concrete slab--plus the thickness of the gravel that you'll add. Compact the soil and crushed stone with a gas or hand compacter.
Forming the Slab
Make frames for the concrete slab using 2-by-4 lumber. Use 3-inch wood screws to attach the frames at all corners.
Then use a level, hammer and wooden stakes and set the drain slope of the frames--this will be the slope of the concrete after it has dried and the frames are removed. Drive the stakes to the outside of the frames, and raise or lower the frames up or down the stakes to create a slight slope in the concrete. Insert 3-inch wood screws through the stakes and into the frames; this will allow you to remove the screws from the frames so you can pull them away from the dried concrete.
Apply releasing grease to the inside of the frames so the concrete doesn't stick to the wood. If you are pouring slabs larger than 20 feet by 20 feet, divide them into 20-by-20 sections and pour them separately.
Pouring the Concrete
Calculate the amount of concrete you'll need by multiplying the length by the width by the thickness and dividing by 27 (which will convert the figure into cubic yards). Lay concrete wire into the frames and support the wire off the ground with concrete bricks or chairs. Another option is to use concrete with reinforcing fiber, which will allow you to skip the wire reinforcement. But concrete with reinforcing fiber will add $5 to $6 per yard to the concrete cost.
Pour the concrete out into the frames, spread it with a hard rake or concrete rake, and smooth the surface with a bull float, which resembles a push broom but with a 4-foot-wide base and aluminum body. Apply a broom or slick finish after the concrete has set for 1 to 2 hours. Finish the concrete around the edges with a concrete edger and remove the frames after 24 hours.
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