Pour a Concrete Floor
A Guide to Concrete Construction
By Monte Burch
Concrete floors are a major component of many buildings, from homes and garages to shops and sheds. Pouring a concrete floor is hard work, and it takes skill, strength and tools. You may wish to have this job done by a pro, but you can do it yourself. The tools can be rented at many rental places, and the skills are not very difficult to learn. If you’re undecided as to whether to do it yourself or have the job done by a professional, the following steps on pouring both a slab or in-foundation floor illustrate the basics and may help you decide.
A concrete slab on which a building is erected is a fairly simple concrete pour, but it takes more work in creating the forms needed to hold the concrete. A pour within a foundation requires little in the way of forming, but in some cases can be a bit more difficult to pour, especially on larger projects. Regardless of the type of pour, or whether you do it yourself or have the job done, the first step is to check with local building codes and regulations, and acquire any permits needed.
Creating a Slab
First step is to lay out the slab. Take your time with this step and make sure you get it right. Lay out the slab incorrectly, and the building can be a nightmare. The slab must be square. Mark the outline of the building with stakes at each approximate corner. Drive a nail into the top of the stake and, using a tape measure, measure diagonally from stake to stake. The measurements must be equal. Move the stakes in or out to create equal diagonal measurements.
Another method is to place string lines on the nails to mark a rectangular perimeter. Measure and mark 3 feet on one string and 4 feet on the adjoining line. The distance between these two marks should be 5 feet. Again, move in or out as needed.
After the corners are determined and the building laid out square, batter boards are used to create a permanent perimeter mark at all corners. These will stay in place until the forms for the slab have been constructed. Two-by-4 stakes are driven solidly in place and boards nailed to their outer edges. The batter board tops should be level with each other. A string line and string level or laser level can be used to make sure all boards are level with each other. Once the boards are established, a string line is run for all sides of the slab. A plumb bob is used on the intersection of the strings to position their crossing points, or the building corners, directly over the nails on the original stakes.
Mark the outline of the slab with lime, following the string lines. Then dig up the area and remove sod and debris. The area is normally recessed slightly, but the top of the slab must be well above ground level or fill level. In many instances the slab is raised and soil filled in around it to create a slope to drain rainwater away from the slab. In some instances local codes may require a footing be poured before the slab. In other cases, a “stiffener” method may be used, digging a deeper area below the frost line around the perimeter of the slab.
The entire area should be well compacted and of a uniform depth. Keep the ground slightly moist as well. The form is then constructed using 2-by-6’s. Stakes are driven into the ground on the back (outside) side of the forms every 3 or 4 feet apart to support the form boards. The stakes should be driven or cut off flush with the tops of the form boards. The stakes are fastened to the form boards using duplex nails or nails with double heads so they can be pulled out after the concrete sets. The forms must be level and at the proper grade or height. A carpenter’s level can be used for small projects, a string level for longer runs, but a builder’s or laser transit is best for larger pours.