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Project Difficulty:
Moderate
Estimated
Project Time: Varies with project
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| Tools and Materials: |
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Rubber boots
Heavy waterproof gloves
Concrete
Garden hose
Wheelbarrows, as needed
2x12s
Hoe
Shovel
Hook or claw hammer
2x4
Bull float or darby
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Regardless of whether you mix your own or have ready-mix delivered to your site, you must work quickly when placing concrete in formwork. If your project is large enough to require a delivery of ready-mix concrete, you will probably need to enlist some friends to help with the pour. Be sure to wear rubber boots, heavy waterproof gloves, and protective clothing, because prolonged contact with fresh concrete mixtures will burn your skin.
Mix your concrete as near to the job site as you can, or have the ready-mix truck park as close as possible. Before placing concrete, check the formwork for proper grade and correct depth. Once you're sure that everything is in order, spray the inside surfaces of the forms and the soil or gravel base with water from a garden hose. This will prevent water from being drawn out of the concrete, which can result in a soft or crumbly surface. Moistening the forms and soil is especially important on a warm and windy day.
For large projects such as driveways, have at least two wheelbarrows for transporting the concrete to the forms. Lay 2x12s across lawn areas to protect them from the weight of the wheelbarrow, and build ramps over the forms so that you don't bump them out of place (Fig. 1).
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1.
Place the Concrete
Begin placing the concrete in the farthest corner of the forms, making piles that are slightly higher than the formwork. Fill the forms completely. Use a hoe to move the concrete; use a shovel to fill low areas (Fig. 2). Concrete is very heavy; therefore, when lifting the shovel out of the concrete, turn it sideways to slide it out. As the concrete is placed, use a hook or a hammer claw to lift up the wire mesh to ensure that it stays in the middle of the pour.
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2.
Tamp Out Air Bubbles
During the pour, you must repeatedly consolidate the concrete by moving a shovel, hoe, or 2x4 up and down vertically to remove all air bubbles. This is especially important near the edges and in corners. Do not overdo it though! If you overwork the concrete, the water will separate and rise to the top, a condition called segregation. Further settle the concrete against the perimeter by tapping the outside of the form boards using a hammer. (Fig. 3)
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3.
Screed the Concrete Level
Once the form is filled and tamped, begin striking off (screeding) the surface level with the top of the forms. Use a length of 2x4 that is slightly wider than the forms. Try to use a straight piece of lumber, but if there is a bow to the wood, screed with the convex side up. Move the screed back and forth as you slide it along the top of the forms. Keep both ends pressed down on top of the forms to force all the aggregate into the concrete (Fig. 4). Fill hollow areas with a shovelful of concrete, and strike them off level. For a large pour, two people can begin screeding as concrete is placed ahead of them.
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4.
Float the Surface Smooth
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Floating is the first step in the finishing of concrete and is done immediately after screeding. The initial floating depresses large aggregates and knocks down small ridges. For a large pour, use a bull float to smooth the surface (Fig. 5). To use a bull float, push it across the surface with the front edge raised a bit; when pulling it back, lay the blade flat to cut off bumps and fill any tiny holes. At the end of each stroke, lift the float and move it over to make a parallel stroke.
For a small pour, use a darby to smooth the concrete. A darby is smaller and easier to control. A darby should reach across half the pour; if it doesn't, use a bull float. Use two hands to move the darby in sweeping arcs across the concrete surface (Fig. 6). Do not allow the edges or end of the tool to dig into the concrete.
Caution: After the first floating, do not do anything else until the water sheen is gone from the surface of the concrete. The time this takes will vary, depending on the temperature, wind, humidity, and type of concrete mix. If you begin edging and further finishing while there is water on the surface, the concrete quality, especially at the surface, may be lessened. Of course, if you wait too long, the concrete will be unworkable.
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