How to Pour a Concrete Slab: A Step-by-Step Guide

Decide the slab's size, thickness, and location. Most patios and walkways are 4 inches thick; driveways and load-bearing slabs are 5–6 inches. Check whether your project needs a permit, and call 811 to have underground utilities marked before you dig — it's free and prevents dangerous, expensive mistakes.

Strip the sod and topsoil and dig down to your slab thickness plus about 4 inches for the gravel base. Keep the bottom level and firm, and rough-grade a slight slope (about 1/8–1/4 inch per foot) away from any structures so water drains off the finished slab.

Spread 4 inches of gravel or crushed stone and compact it in thin lifts with a plate compactor. A solid, well-drained base is the single most important defense against a cracked, settling slab. Not sure how much stone to buy?

Build the perimeter forms from 2x4 or 2x6 lumber, staked every 2–3 feet and braced so they won't bow under the weight of wet concrete. Check that the forms are level (or intentionally sloped for drainage) and square by measuring the diagonals — they should be equal.

Lay welded wire mesh or a rebar grid on chairs so the steel sits at mid-slab depth — reinforcement does nothing lying on the ground. For interior slabs, put down a 6-mil poly vapor barrier over the base first to keep ground moisture out of the finished floor.

For anything over about 1 cubic yard, ready-mix truck delivery is cheaper and far easier than mixing bags by hand. Aim for a workable 4–5 inch slump, and resist the urge to add water on site — it weakens the concrete. Figure out exactly how much to order (plus 10% overage) before you call the plant.

Start pouring at the far corner and work back toward your exit. Move and spread the concrete with a rake or come-along, pushing it into the form corners. Then screed: drag a straight 2x4 across the top of the forms in a side-to-side sawing motion to strike off the surface perfectly level.

Run a bull float over the surface to fill voids and bring up the cement paste. Then wait — do no further finishing until the shiny "bleed water" has evaporated, or you'll trap it and cause scaling. Once the sheen is gone, round the edges with an edger and cut control joints (in feet, spaced no more than 2–3× the slab thickness in inches; at least 1/4 of the depth deep) to control where the slab cracks.

For exterior slabs, drag a broom across the surface for slip resistance. Then cure the concrete by keeping it damp (or applying a curing compound) for at least 7 days — this is what actually builds strength. The slab is walkable in 24–48 hours and reaches full strength at 28 days. Wait the full 28 days before parking vehicles on a new driveway, then consider sealing it.