A concrete job done poorly is much more expensive to remove and replace than paying to have the job done by a qualified contractor in the first place. Check with your local building officials. They are there to help you. For exterior concrete, decide where the rain water will go. Proper drainage is essential. Slope the concrete surface at least 1/8” per foot, ¼” is better.
Lay out your project using stakes and a string line. Excavate all vegetation and organic matter from the location. Use a level and string line to guide your form setting. Brace your forms every 3-4 feet and at every joint. Prepare the sub grade so that the minimum concrete thickness is at least 4” for residential flatwork. Foundations must meet local codes. Uniformity of concrete thickness and sub grade is important. Sub grade must be damp, compacted and free of standing water.
Wire mesh is a waste of time and money because it is seldom installed properly. Depending on the application, use steel rebar on plastic chairs, or order fiber in the concrete, or both. A common specification for residential flatwork is 3/8” rebar on 18” centers each way.
Concrete joints control where the concrete cracks. Plan your joints before pouring. Typically, control joints should be spaced 10 to 15 feet apart, making the sections as nearly square as possible. Joints need to be at least ¼ the depth of the concrete. For example, if you have a 4” concrete depth, the joint should be at least 1” deep. Joints can be hand tooled, saw cut, or formed. Formed joints are commonly made from redwood because of its resistance to rotting.
Ready mix producers will help you select the right mix for your job. Depending on your location and application, a typical specification might be: 3000 psi concrete in 28days, air entrained, and a 5” slump. Also, designate the coarse aggregate needed, such as 1” or 1 ½” crushed limestone, pea gravel, or native gravel. Calculate the amount of concrete required by using the online calculator at www.cooperconcrete.com/calculator.htm. Be sure and order enough. It is better to have some extra concrete at the end of the job, rather than wait for the extra load and pay a short load fee. The ready mix producer will dispose of left over concrete still in the truck.
Concrete must be discharged as close to final position as possible. Avoid dragging the concrete long distances. The concrete will segregate, quality will suffer, and it will wear you out. Be prepared to unload the concrete in 30 minutes or less. That means having plenty of people to help, especially if you are using wheelbarrows to move the concrete from the truck to the forms. The concrete will be delivered to the nearest accessible point over stable soil (able to support 65,000 lb.) The truck needs a pathway at least 12 feet wide and 14 feet high (watch for tree limbs and power lines). Existing residential concrete is not usually designed for truck traffic, so avoid bringing trucks over curbs, sidewalks, or driveways. The discharge chutes can reach approximately 12 feet from the back of the truck.
Concrete should be struck off or “screeded” as it is placed. A straightedge (straight 2”X4” or magnesium screed) is used to screed the concrete. Immediately after striking off, and before bleed water appears, the concrete must be bull floated and the edges formed with an edger. After bull floating, no finishing operations should take place until the bleed water has completely evaporated. When the concrete is firm enough that a person’s weight on it will make no more than a ¼” imprint, final finishing operations may begin. Here is where opinions differ. Many times concrete is overfinished. For driveways and sidewalks, broom texturing may be performed after floating and without troweling first. Many contractors prefer to trowel first, then broom. Troweling does smooth and densify the surface, but you run the risk of overfinishing and causing surface defects. For smooth surfaces such as house foundations and garage floors, troweling will give the surface a smooth, hard surface. Begin with the trowel nearly flat, then increase the angle with each subsequent pass. Do not sprinkle water on the surface of the concrete because it will weaken the surface and can cause dusting, spalling, or crazing.
From a quality standpoint, the most important, yet most neglected aspect of placing concrete is curing. The most practical and effective method of curing is spraying a membrane curing compound on the surface immediately after finishing operations are completed. Some people believe using a sprinkler on the concrete helps, but alternately wetting and drying the concrete can cause more problems than it solves. Other methods such as wet burlap, plastic sheeting, or waterproof paper can be used, but may cause cosmetic flaws. Good coverage is essential. Make two passes at right angles to each other. Using a pigmented curing compound will allow you to see that you have covered the entire surface. The only time you would not use a curing compound would be in a situation where you are applying a special finish that is not compatible with the chemicals in the curing compound. These situations are rare, and in those cases you should use the wet burlap, plastic sheeting, or waterproof paper method. Remember, always cure the concrete.