How to Build Concrete Construction Slabs
Concrete sidewalks, driveways and patios are durable and practically maintenance-free alternatives to tile or asphalt. The concrete may be stained, design features may be etched into the concrete, or tiles or bricks may be placed along the border to personalize a space. Proper procedures should be followed when constructing a concrete slab to assure durability and strength.
Items Needed:
- Air entrainment is optional
- Blocks
- Cement mixer
- Concrete tamper
- Excavator
- Fiber additive is optional
- Float
- Gravel
- Hammer
- Level
- Mesh
- Nails
- Screed
- Shovel
- Stakes
- String
- Water source
- Wood
- Excavate and backfill a 24-inch trench, mechanically vibrating after each 6 inches of backfill to properly compact the subgrade for the concrete slab. Proper subgrade preparation will assure that the soil does not settle beneath the concrete later resulting in cracks in the concrete. The un-compacted trench will serve as drainage for rain and other water.
- Fill the area with 2 inches of gravel with a shovel to allow for proper drainage, and tamp the gravel firmly.
- Place stakes at each end of the area for the framing and tie a string connecting all the stakes.
- Position a level on the top of the string to determine if additional fill is needed to level the area.
- Construct proper level framing to avoid expensive shimming or cutting of framing and unleveled framing lid lines.
- Design the framework with control joints to allow for movement caused by shrinkage or temperature changes. A straight-line crack is preferred to a zigzag line or thorough breakage.
- Utilize proper water to cement ratios, as water permeability increases with a water-to-cement ratio greater than 50 percent. The quality of the concrete is affected when the cement ratio is higher than the water ratio. The Uniform Building Code of 1997 dictates a maximum of 50 percent water-to-cement ratio when mixing concrete; however, severe sulfate conditions dictates a maximum ratio of 45 percent.
- Add air entrainment to the concrete mix in climates with frigid temperatures to avoid cracks in the concrete due to expansion.
- Space the joints properly and cut the joints to the building code for the location. A grooving tool should be utilized to cut the joints in newly poured concrete. It is preferential to use a saw to cut the joints as the concrete hardens, usually within six to 12 hours after finishing in hot temperatures.
- Support the mesh with cement blocks before pouring the concrete to lift the mesh off the ground and consider adding fibers to the concrete mix for extra strength and durability.
- Pour the concrete and level the concrete by sliding a screed across the top of the framing boards.
- Remove lumps in the concrete by sweeping a float in an arc-shaped motion. Do not allow the float to dig into the concrete.
- Flood the concrete with water, utilize a canvas covering to keep the concrete wet, or utilize a chemical membrane to properly cure the concrete. Proper curing delays the drying and shrinkage time to allow the concrete to gain strength while retaining moisture in the slab.