How to Pour a Concrete Slab
A slab — a patio, shed floor, or walkway — is one of the most achievable DIY concrete projects, and success comes down to a solid compacted base, the right thickness, and not rushing the pour or the cure. Work through the steps and tap “Add to my materials list” as you go.
1Excavate and build the forms
Dig out the area and build level form boards (2×4s give a 3½” slab, 2×6s a thicker one), sloping the forms about 1⁄8–1⁄4” per foot away from any structure for drainage. The calculator gives the dirt to dig and haul.
2Compact a gravel sub-base
Add and compact about 4” of crushed-stone sub-base, keeping it damp as you tamp for a stable, well-drained foundation under the slab. The calculator gives base gravel by the ton or yard.
3Lay vapor barrier and reinforcement
Where moisture matters, lay a 6-mil poly vapor barrier, then set 6×6 welded-wire mesh or a #3 rebar grid at mid-depth on chairs (about 2” up in a 4” slab) to control cracking. The calculator sizes the vapor barrier and tape.
4Pour, screed, float, and finish
Place the concrete (3,000–4,000 psi is ideal for home slabs), screed it level with the form tops, float to bring up the paste, run an edger around the perimeter, then broom for a non-slip finish. The calculator gives cubic yards and bags. Never add water to loosen the mix — it weakens the concrete.
5Cut control joints and cure
Tool or saw control joints ¼ of the slab depth (~1” on a 4” slab), every 8–12 ft, so the slab cracks where you want it to. Then moist-cure for 5–7 days; wait 48 hours before foot traffic and ~28 days for full strength.