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Concrete is an age-old pillar of civilization, on a par with beer, steel and the plow. Master concrete (we're talking about simple backyard cement and water here, not engineer-grade flexible concrete.) and you can build a backyard empire--starting with a place to fire up your grill.
For small jobs, you can buy bags of cement that already contain sand and gravel--you just add water. On larger jobs, it's more economical to buy cement and aggregate, and combine the ingredients in a motorized mixer. These rent for about $50 a day and can be towed home. Cement comes in 94-pound bags; about six will make a cubic yard. The sand-and-gravel aggregate should include a range of sizes, from grains to 3/4-in. stones. If the aggregate in your area is too fine, add 3/8- to 3/4-in. gravel.
As for time commitment, you can easily pour a small slab in an afternoon. Here are the steps to get the job done.
Step 1: Tools of the Trade
Edger: To round the corners of a pad, run the edger back and forth while pressing down.
Trowel: A steel surfacing tool for an extra-fine finish. It's optional for outdoor work.
Groover: To make contraction and expansion joints, which help control cracking, use the groover to section off the concrete.
Step 2: Create Form
Step 3: Excavate Soil
Set the form in place and shave away soil from high spots and check with a level. A slight slope of about 1/8 in. per foot helps shed water.
Step 4: Stakes
Step 5: Screw in Stakes
Step 6: Mixing Ingredients
Step 7: Coarse Aggregate
When the drum is about three-quarters full, gradually add more water--the exact amount will vary, depending on the moisture content of the aggregate.
When the mixture reaches a gray/green color with hardly any of the rock color showing through, stop the mixer and pull out a small handful. Form it into a 3-in. ball and toss it from one hand to the other. If it crumbles, it's too dry. If it splatters, it's too wet. Cautiously add a little water or more aggregate and cement to correct the consistency, then run the mixer for 3 more minutes.
Concrete from a relatively dry mix will always be stronger than that from a wet mix, so it's best to err on the dry side. After touching the concrete, immediately give your hands a thorough wash.
Step 8: Prepare to Pour
Wash your hands immediately after handling wet concrete. It contains alkaline compounds like calcium oxide that can irritate skin, can cause up to third-degree burns.
Step 9: Fill Form
Step 10: Spread With a Screed
Then, steadily saw the screed board side to side while moving it along the form. If you find a low spot, fill it and saw through that area again.
Step 11: Smooth With Float
After screeding, wait a few minutes before using the float. When the surface appears dull, hold the float on the concrete with extra pressure on the trailing edge. Run it along the pad edges and across the surface in wide arcs.
Step 12: Edge the Slab
Step 13: Trowel Finish
Concrete cures best between 50 F and 70 F. It achieves most of its strength--60 to 75 percent--during the first week, and about 95 percent over the first three weeks. To make sure the concrete dries correctly, keep the job damp for five days by covering it evenly with a plastic vapor barrier or by using a sprinkler. Alternatively, you can also apply a curing-and-sealing compound.