05/09/2026
Concrete doesn't flex. When the ground beneath it shifts, settles or erodes, the slab cracks. How to prepare your ground for a concrete slab:
1. Mark the area and set your grade. Drive stakes at each corner, run string lines at your finished slab height and set a minimum 1/8" drop per foot for drainage. Use a line level, don't eyeball it.
2. Clear your site by stripping everything organic and all topsoil. Dig until you hit firm, consistent mineral soil with no visible organic matter.
3. Assess your soil conditions. Clay expands when wet and contracts when dry. It may need a deeper base or geotextile fabric. Sandy soil drains well but needs thorough compaction. Loamy or organic heavy ground must be fully excavated.
4. Excavate to the right depth. Total depth = slab thickness + base thickness. A standard patio needs ~8" total (4" slab + 4" gravel). A driveway or garage slab needs 10-12". Check depth consistently with a tape measure from your string line. Don't fill low spots with extra concrete.
5. Compact the subgrade. Run a plate compactor over the entire area in overlapping passes, north to south then east to west. The surface should feel firm and solid underfoot. Use a hand tamper along the edges and corners.
6. Add and compact your gravel base. Use angular crushed gravel, not pea gravel or round stone. Spread in 2" lifts and compact each one fully before adding the next. Compacting in lifts gives you a denser, more stable base than applying all at once.
7. Manage moisture. For enclosed slabs, lay plastic sheeting over the compacted base before pouring. Overlap seams by at least 12" and run sheeting up the inside faces of your forms.
8. Add reinforcement. Any slab carrying heavy loads needs wire mesh or rebar. Elevate mesh off the base so it sits in the middle third of the slab. Use rebar on 18-24" centers for driveways and garage slabs. Pair with control joints every 8-12'.
9. Set your forms. Use 2x4s for 3.5" slabs, 2x6s for 5.5" slabs. Align boards with your string lines, stake every 2-3' and confirm top edges match your finished slab height. Coat the inside faces with a form release agent so they pull clean after the concrete sets.
10. Walk the entire project before you pour. Confirm grade, slope, form alignment, reinforcement position and v***r barrier. Fix any problems before concrete hits the ground.
