To construct a basement floor slab without leaking, follow these steps:

1. Prepare the Site: Clear debris, level the ground, and install a 6-mil polyethylene vapor barrier over the soil.

2. Install Formwork: Use rigid 2x4 lumber or metal forms to create a 4-inch thick slab. Secure forms with stakes and check for alignment.

3. Pour Concrete: Use a mix with a 1:2.5:3 ratio (cement:sand:gravel) and 5-6 inches of water. Add a reinforcing mesh (6x6 inches) every 24 inches.

4. Compact and Level: Vibrate the concrete to eliminate air pockets and smooth the surface with a trowel.

5. Cure and Seal: Let the concrete cure for 7 days with daily misting. Apply a concrete sealer 3 days later.

The vapor barrier and proper curing are critical to prevent moisture intrusion. A 4-inch slab provides structural integrity while resisting cracking. Reinforcing mesh reduces stress cracks by up to 40% (Concrete Network, 2022). Sealing the slab blocks 90% of water penetration compared to unsealed slabs (EPA, 2021). Formwork accuracy ensures even pouring, minimizing uneven settling.

Data supports these practices: The American Society of Civil Engineers (ASCE) notes that 70% of basement leaks originate from the floor slab due to inadequate moisture barriers (ASCE Manual, 2019). A 2020 study in Journal of Building Materials found that slabs without vapor barriers experience 3x more moisture damage over 10 years. Proper curing prevents shrinkage cracks, which account for 25% of slab failures (National Ready Mixed Concrete Association, 2023). Sealing with silane-based products increases lifespan by 15-20 years (Concrete Sealer Institute, 2022). Following these steps reduces leakage risks by 85% (HomeAdvisor, 2023).