Rebar, or reinforcement bars, are long, round, heavy bars of steel placed at intervals in concrete floors and slabs for additional strength, stability and to prevent the concrete from breaking apart in large chunks. More reinforcement may be required in locations that experience seasonal freezing than in a constant, warm environment.
Rebar is used in a variety of construction settings. Rebar can be placed vertically in cinder-block walls and foundation footings, and can be laid horizontally within slab and footing forms. Depending on your local building code regulations, rebar may be laid in a grid-like pattern or in a mesh. Contact your local government building department for information regarding specific codes for concrete floor construction.
Rebar comes in a variety of sizes determined by the ASTM (American Society for Testing and Materials) International. Rebar is constructed in long, round tube-like lengths ranging from 20 to 60 feet. Different grades of rebar are available for use in various building scenarios. Refer to your local building code office and International Residential Building Code guides for national, state and local specifications. Rebar 40 grade offers a minimum-yield strength of 40,000 pounds per square inch; grade 60 offers 60,000, and grade 75 offers 75,000. Rebar is also available in metric grades of 280, 420 and 520 with the same respective pounds per square inch of yield strength. Bar designations range from 3 to 18, with respectively increasing weight in pounds per foot.
Measuring the area you’re pouring concrete into helps determine the amount or formation of rebar for your situation. To measure a cement floor slab such as a garage or basement floor, measure the length by the width to get square footage of space. If you already know local requirements for rebar per square foot, multiple the square footage of the intended cement floor slab by the required rebar per square foot.
A cement basement floor, patio or driveway commonly uses 1/2-inch, or #4, rebar; the rebar is typically laid out in a grid pattern. Rebar corners in such grids are connected with rebar tie wires to help hold the square grid shapes. The actual spacing of horizontal grid squares is determined by your local building codes; squares of 12 inches to 18 inches are suitable for basement flooring as well as driveways in most locations. The actual amount of rebar or rebar mesh spacing is determined by the square footage and the location -- for instance, interior flooring or exterior driveway -- where you're pouring cement.