Concrete Slab Basics
Concrete will leave your legacy on this earth for over a century, if not longer. Once concrete has been formed and poured it turns solid as stone, can take the weight of thousands of tons from cars and trucks to homes and factories, it can be shaped and molded into circles and tubes from as small as three inches wide to as large a nuclear reactor. While concrete may be the most diverse construction product in the world, it is certainly the most unforgiving.
When pouring a concrete slab, it is crucial to achieve a perfect flat surface on all sides, both above ground and below. The only way to have success with the final product is by creating the form perfect. Form work can be easily underestimated by any person with the "I can do it my self" attitude. While a small slab can be accomplished by one person, a larger slab, say 10'x10', having some help setting forms is a must.
When you have your blueprint in hand, your tools, and two looming dates, one with a building inspector and the other a concrete truck, you tend to get a little nervous. Don't worry, it can be done.
Always start with a layout of the entire property. Begin by measuring off of the property line with a long tape or measuring wheel to verify where a slab will exist. You will need to make a square measurement by measuring from the property line on the side of your house and to the road.
Don't break out the shovels yet. Call all of the utility companies in your area and have them mark the lines. Not only could you cut a phone line, you could hit a power line and possibly kill yourself. Don't laugh, it happens somewhere in your area everyday.
Once you've check for utility lines, check the septic. You can't pour a slab over the septic tank. Of course if you have your plan approved by the county building inspectors, then they wouldn't have let you build on it to begin with.
Once the dangerous underground obstacles have been located or eliminated (or they were never there to begin with), then it's time to set the batter boards. Batter boards are temporary boards set up so string lines can be attached between them. These lines represent the final height, length and depth of the slab.
Setting up batter boards is easy. Simply start by marking the corners of the slab with a small stake. From these stakes set up two boards pointing towards each end of the next corner of the slab. Don't set them right on the mark; back them away about three or four inches. This way the strings can intersect freely over the actual mark.
Drive some stakes into the ground next to the batter boards you just placed on the ground. Now you need to find the lowest spot of ground on the corner of your slab. This can be achieved by a sight level. Measure up at least six inches from the highest spot and level the other stakes from that mark. This will ensure your slab is at least six inches out of the ground and prevent water from rising onto the slab and possibly in your structure.
Now that the batter boards marked nail them in place. Once they are all leveled and nailed, measure between each batter board and mark them with a pencil. To square a slab, you need to measure from corner to corner, adjusting your marks until each measurement is the same.
Once the marks have been laid out on the batter boards and all of the measurements are accurate, place a nail into the top of the board on your mark. Tie string line from each nail and batter board pulling them tight as possible until your slab is represented by the strings. You are now ready to set form boards.