Concrete slabs require an internal reinforcement structure, much like a skeleton, to help distribute the load weight placed on the slab and to provide the concrete with a support structure to help hold it together. The process to install rebar for a concrete slab, also called "placing" or "placement," is not as difficult as it is physically demanding work. If you know the steps to install rebar for a concrete slab, you will be able to do the work quickly and with less effort.
Locate the notation on your building plans that tells you the spacing for the rebar. The information will be a part of the note that tells you what type of rebar is going into the slab. For example, the note may read "44 #4 @ 18;" read this as "44 (amount) #4 bars (the size) are to be placed in the slab area with an 18-inch space between each individual bar."
Use a tape measure and orange marking paint to mark the bottom of the slab area with the building plan spacing details for the rebar placement. You don't need to spray a line of paint down the entire length of the slab. You only need to put a six-inch spray mark every so often to help you keep the bars running in straight lines as they are put down. Do this for one direction of spacing only, for example, the bars that are north to south in the slab.
Lay the bars so they follow your orange marks. When you are done, you should have one direction of bars in your slab evenly spaced at 18 inches.
Adjust the clearance of the bars. On most sites, the end of each line of bars, or the first and last bar, must be three inches away from the face of the slab form. Check the notes section of your prints to make sure this holds true for your slab.
Adjust the splices of the bars. Each bar must overlap the next one to splice. There will be a note on your plans either directly on the page or in the front in the General Notes section that will specify the splice for each size bar on your job. When you have the bars adjusted, tie the splices together using tie wire and lineman's pliers. Wrap the tie wire around the rebar and twist the ends together with the pliers. Put a tie at each end of each splice.
Measure and mark the spacing for the bars that will run in cross direction to the ones you just tied. Mark the bars you just placed and not the ground. Do not mark all the bars, but as in Step 2, just mark enough to keep the bars you will be placing in a straight line.
Lay the next direction of bars down and repeat the process of adjusting the clearance and setting the splices for this direction just as you did for the bars in the other direction. The two directions of bars crossing each other is called a "mat."
Tie your mat together at every intersection of the bars using tie wire and your lineman's pliers. Simply loop wire under the intersection and twist the two ends of the loop together.
Raise the mat. Place a cement brick under the intersection of two bars every four feet throughout the entire mat.
Some mats are not required to have every intersection tied. Check with your building inspector to find out what you are required to do.
Do not assume that generic or "usual" spacings, clearances and other details apply to all mats. Check the specifics of your plans or you can fail inspection and have to do the work again.