How to Pour a Concrete Slab
Whatever size slab you decide to pour, you will need to know how big you want it. Square footage is determined by measuring each side of the slab. For instance, a 10×10 slab is 100 square feet. You simply multiply the sides together. To find the volume of concrete it becomes much more difficult and easily be done wrong, ruining your concrete delivery. I recommend any homeowner go to www.concrete.com and use the concrete calculators and conversion tables. They will calculate the volume, yards, square footage, and many other calculations, down to the fifth decimal place. They even have one that converts it to weight just incase you wanted to know how many tons of concrete you will wheelbarrow.
Now that your square footage is decided, its time to build the forms. Use 2×4 studs for forms and place them directly on the ground. Nail the forms together wit 12d duplex nails. These nails have a raised head that can be easily pulled out again when you pull apart forms. Drive stakes into the ground around one side of the form. Use a tape measure and measure corner to corner across the forms. Now measure the other diagonal across the forms. Do they read the same measurement? If not, you will need to adjust the forms until they become square by pushing or pulling each corner of the forms. Once you have the same measurement from each corner of the slab, drive the remaining stakes in the ground behind the form.
Scrape out all the debris that is in the slab such as grass, leaves, roots or twigs. Pull a string line over the top of the forms stretching from one side to the other. Measure down with a tape. You should have 4-inches between the string and the ground. Use a 2×4 that will fit inside your form board as a screed to flatten the dirt uniformly. If you have a large slab and you’re worried about it getting stiff before you can finish it, then place a plastic vapor barrier inside the forms. This will prevent the ground from immediately absorbing the moisture from the wet concrete.
Now its time for the pour. Start your pours in the farthest spot away from the truck and work your way to the closest. This way he can drive forward as you pour the slab. Use the chute from the truck in a slow sweeping manor so as to not pile it up in mounds. As you sweep across from one side of the slab to the next, have the driver pull forward a foot at a time. After about 5 feet of the slab is done, have the driver stop pouring concrete. Go back the original spot and screed a long 2×4 over the tops of the form. Have a friend help you on the other side of the slab. Work the screed back and forth as you pull it forward. Any mounds will be knocked down and any pits should be filled in with a shovel full of concrete and re-screeded. Continue pumping out concrete and continue the previous steps until the slab is complete.
Now it is time for the finish. Use a bull float to smooth large areas of concrete at one time. Hand trowel around any edges near the form or use an edger trowel to create an embossed band around the slab. Finish with a broom finish if you want a more gripping surface, or use the bull float several times for a smooth finish. If moneys not an issue and you want a perfectly smooth slab, rent a motorized concrete finisher. It’s a machine the size of a floor buffer and has four rotating trowels for a base that spin around like a fan. As the concrete hardens, you place the machine on the surface and start it up. Drive the finisher in large circles over several passes. Add small amounts of water from a water bottle or cup to help smooth the finish. The more you use the machine, the smoother it gets.
