How to Pour a Concrete Slab

A concrete slab for a patio, shed base, or small walkway is a manageable DIY project - the key variables are proper site prep, correct concrete volume calculation, and having enough help on pour day. Concrete waits for no one once it's mixed.

Step 1: Calculate Concrete Volume

Use the Concrete Calculator to get cubic yards - enter length, width, and thickness. A standard patio slab is 4 inches thick; driveways need 6 inches. Order 10% more than calculated. Most ready-mix trucks deliver a minimum of 1 cubic yard; for smaller projects, use bags.

Step 2: Prepare the Site

Excavate 6-8 inches below the finished surface level (4 inches for the slab + 4 inches for gravel base). Compact the soil with a plate compactor. Add 4 inches of compacted gravel base. Check that the base is level and slopes away from structures (1/8 inch drop per foot minimum).

Step 3: Build the Forms

2x4 lumber makes forms for 4-inch slabs; 2x6 for 6-inch slabs. Stake the forms level at the correct height. Brace the outside of forms every 2 feet to prevent blowout. Oil the inside of forms lightly with vegetable oil for easier removal.

Step 4: Add Reinforcement

For slabs larger than 6x6 feet, add #3 rebar on 18-inch centers or 6x6 inch welded wire mesh. Support the reinforcement on rebar chairs so it sits in the middle of the slab thickness. Cut control joints 1/4 of the slab thickness deep to guide where the slab will crack.

Step 5: Pour and Spread the Concrete

Pour starting at the far end and work backward toward the truck. Spread with a screed board resting on the forms, pulling it in a sawing motion. Work quickly - concrete is workable for 30-45 minutes. Have at least 2-3 people for any slab over 50 square feet.

Step 6: Finish and Cure

Smooth with a bull float after screeding. Wait for surface bleed water to evaporate before finishing. Use a broom for slip-resistant texture. Cover with plastic sheeting immediately after finishing. Keep covered and moist for at least 7 days. Avoid foot traffic for 24 hours, vehicular traffic for 7 days.

Pro Tips

• Never add water to concrete to make it easier to work - it weakens the mix significantly.
• Pour in mild weather: avoid below 40F or above 90F.
• Control joints prevent random cracking - space them 2-3x the slab thickness in feet.
• Have all tools and help in place before the truck arrives.
• For bag concrete, rent a mixer for more than 10 bags.