A durable and economic material, concrete can be used for a number of projects. Randy Williams of Quikrete offers a lesson in the basics of making and using concrete.
Concrete is one of the most durable, economical and versatile building materials, used on everything from driveways to lighthouses.
Concrete is composed of a binding medium (usually Portland cement), aggregate and water. Portland cement is a mixture of minerals fired in a kiln, combined with gypsum ground fine. It's sold in 1-cubic-foot bags weighing 94 pounds each. A combination of fine and coarse aggregate makes up 60 percent to 75 percent of a given volume of concrete. Fine aggregate is sand that will pass through a 1/4-inch screen. Coarse aggregate consists of gravel and crushed stone between 1/4 inch and 1-1/2 inch in diameter.
To determine how much concrete is needed to fill a rectangular or square surface, use either of the following formulas:
- [Width in feet x length in feet x thickness in inches] divided by 324 equals cubic yards of concrete needed
- [Width in feet x length in feet x thickness in inches] divided by 12 equals cubic feet of concrete needed
When working with concrete, always wear a mask or respirator and gloves for protection. Mix the concrete in a large bucket or wheelbarrow until you get a mass of uniform color without brown or gray streaks. For surfaces that will be exposed to moderate weather and wear, a mix of 1 part cement, 2-1/2 parts sand and 3 parts gravel is recommended. For projects not subject to wear and weather, use 1 part cement, 2-3/4 parts sand and 4 parts gravel. Use a metal trowel to spread the concrete, eliminating all air pockets.