Make Concrete

Concrete has many, many uses, from building patios and driveways to casting sculptures and ornaments. It is versatile, weatherproof, and inexpensive. However, in order to use concrete, you must be willing to invest the required effort.

Steps

1. Plan your project carefully. Having a detailed plan for your project will help you avoid a lot of problems later on.
   • Decide on the area to be concreted, draw up a plan, and write in all measurements.
   • Determine the finished levels of the work and write these levels on the plan.
   • Determine the thickness (depth) of the concrete and write it on the plan. 4 in. (10 cm) depth is standard for driveways and garages used by passenger vehicles, but not for heavy trucks.
   • Remember to allow for drainage and ensure that water will not run to undesired locations. Provision a minimum drop of 1" for each ten feet of slab (1.2cm per m), although 1.5" drop for every ten feet of run (1.8cm per m) is preferred.
2. Purchase or gather the raw materials. Generally, you will need Portland Type I (general use cement) or Type II (used for structures in water or soil containing moderate amounts of sulfate, or when heat build-up is a concern) cement, masonry/builder's sand or other clean sand, and gravel or crushed limestone.
   • Calculate the volume of concrete required by multiplying the thickness in feet by the square footage of the area to be concreted.
   • Purchase as much concrete as needed for your project. 1 square foot (.093 sq. m) of 4 in. (10 cm) deep concrete requires 50 pounds (22.7 kg) of concrete mix.
   • Portland cement generally comes in bags weighing 96 lbs (43.5 kg) and should be handled with care. Depending on the size of your project, a truck may be needed to assist in hauling.
3. Assemble or buy a mixing container. Build a mixing box from wood planks or use a sturdy wheelbarrow to mix the materials. If your project is large, rent a mechanical mixer to do reduce the human labor.
4. Build the forms. In order to contain the wet concrete, assemble the forms along the outer edges of the area you will be placing the concrete in.
   • Use timber boards to assemble the forms.
   • Brace the boards securely, ensuring that they are strong enough to support the weight of the concrete.
   • Check that the form work is level.
   • If you are plumbing underneath the concrete, ensure it is in the proper place.
   • Confirm that the dimensions of the forms match the dimensions laid out in your plans.
5. Mix the cement and sand. Prepare your dry mix by mixing the cement mix and sand. There are a few common mixtures and methods for concrete preparation.
   • Option 1: A basic mixture for mortar (not concrete) is made using a 1:2:3 ratio of water to cement to sand by volume.
   • Option 2: General purpose concrete is created using a 1:2:3 ratio of cement to sand to gravel by volume.
6. Add the gravel or crushed stone. Incorporate the gravel or crushed stone in the dry mixture.
   • Add gravel or crushed stone at a ratio of up to 5 parts gravel per 1 part cement and sand mixture.
   • The gravel doesn't adversely affect the tensile strength of the concrete unless you add too much. If the gravel doesn't leave enough cement paste to fill the cracks between the gravel, you have added to much.
   • Adding too much gravel can also make it difficult to get a smooth finished surface on the cured concrete.
7. Add water. Begin by adding water to the mixture slowly, mixing continuously until the concrete becomes plastic enough to place in your form.
   • The plastic character of the concrete is measured in "slump", which is determined by filling a metal "slump" cone with the mixed, wet concrete, lifting the cone off gently, then measuring how far the concrete sags, or slumps. The typical "slump" of good structural concrete is about 3 or 4 inches (7.5 or 10 cm).
8. Thoroughly mix the concrete. Continue mixing until the concrete has a uniform consistency.
   • The texture should be even throughout the mix, with no pockets of dry material.
   • Continue mixing for two or three more minutes to begin the hydration process, which is ultimately what causes the concrete to harden.
9. Pour and float the concrete. Add the concrete to your form, tapping all the edges to remove air pockets, and let it settle in evenly and firmly.
   • Using a magnesium float or a smooth flat board, level the concrete across the top.
   • Do this by dragging the tool, tilted slightly upward on the leading edge, across the surface of the concrete.
   • This process is known as "floating" and will float the fine cement paste to the surface.
   • The fine paste is malleable and easy to smooth and finish either by brushing, brooming, or troweling when it begins to "set" or harden.
10. Let it dry and finish it. After floating, leave the concrete alone until it becomes firm enough to finish without leaving tool marks.
    • Lay out "knee boards" or pieces of plywood that you can walk on without sinking into the concrete.
    • Crawl onto the slab with the appropriate hand tools and finish the concrete into a smooth surface.
    • For very large slabs, you will need a "bull float" and possibly a power troweling machine. This is an investment that is better left to professionals.
    • After the concrete is placed and finished, cover it and protect it from extreme temperatures and rain for a few days.
11. Clean up the work space. Gather and clean all the tools and the mixing container as soon as you are finished with them. Cured, hard concrete is difficult to remove.
    • Take special care to clean rented equipment, as the rental company often will charge an additional cleaning fee when you return them.

Tips

• There are many additives for use with concrete mixes, but these are usually only available or practical with ready mixed concrete. They can reduce shrinkage (which causes cracks), increase working time speed up the setting process, and change the color and/or texture of the finished product.
• Make sure the buckets are small enough that you can lift them to dump them. A five gallon bucket full of dry Portland cement or sand is about 45 pounds (20 kg).
• The higher the cement to sand ratio, the stronger the concrete.
• Allow yourself time to complete the whole process when you begin. Depending on the size of the area, start early in the morning and gather all the help you can.
• If you are mixing more than 5 or 6 cubic feet (.14 or .17 cubic meters) to use at one time, seriously consider renting or borrowing a concrete mixer.
• Use buckets to give the most precise mixing proportions, rather than a shovel, since "scoops" can vary significantly.
• To make concrete stronger, 3/8"-1" (0.95 - 2.5 cm) rebar rods can be pushed into the wet mix or suspended before the pour. This will help with any tension loads. Mixing in fibers (glass or plastic) can help too.
• Use premixed concrete products if you are not confident in your ability to measure the basic materials. These are pre-measured and packaged for handyman use, and the package will have detailed mixing instructions and applications described on it.

Warnings

• Portland cement can cause burns to unprotected skin.
• Wear rubber boots and gloves to protect your hands and feet if you are working with the wet concrete.
• Do not breathe the dust from the Portland cement, or allow it to get in your eyes. Wear a respirator and safety goggles.

Things You'll Need

• Portland cement cement (Type I or II)
• Clean sand (fine aggregate)
• Gravel (coarse aggregate)
• Water supply
• Waterproof gloves
• Measuring tools
• Mixing container (wheelbarrow or other container)
• Mixing tools (shovels, hoes)
• Finishing tools (wood or magnesium float, trowel, edger, jointer, finishing broom)

Related Articles

• Mix Portland Mortar
• Mix Cement
• Pour Concrete
• Finish Concrete
• Build Forms for a Curving Concrete Sidewalk
• Build a Straight Form for Concrete
• Drill Into Concrete
• Measure Concrete for Patios
• Make Concrete Even Stronger

Sources and Citations

See also

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• Tie Rebar
• Build a Concrete Sidewalk
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• Figure Concrete Yardage
• Acid Stain Concrete

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