How to Pour a Concrete Patio Slab
Forms, base, reinforcement, the pour and finishing for a DIY concrete patio, with materials for a 10×12 slab worked out.
Pouring a small concrete patio is a realistic DIY project, but it’s unforgiving: once the concrete arrives you have a limited window to place and finish it. Almost everything that goes wrong comes from preparation, so most of this guide is about the work before the pour.
Materials for a 10 × 12 ft patio, 4” thick
| Item | Quantity |
|---|---|
| Concrete | 1.63 cu yd (incl. 10% extra): 74 × 80 lb bags, or 1.75 yd of ready-mix |
| Gravel base, 4” | 2.39 tons (1.7 cu yd) |
| Rebar, 18” grid | 13 × 20 ft bars, about 14 chairs, tie wire |
| Forms | 6 × 8 ft 2×4s (44 ft of edge), about 16 stakes |
At 1.63 cubic yards, ready-mix is the practical choice. Mixing 74 bags by hand means several hours of hard work, and the first batches start to set before the last ones go in.
1. Check rules and call 811
Some towns require a permit for patios over a certain size or close to a property line. In the US, call 811 a few days before digging so buried utilities are marked.
2. Excavate and build the base
Dig out to the slab thickness plus the base depth: 4” + 4” = 8” for this patio, measured from the finished surface. Compact the soil, then spread and compact 4” of crushed gravel. A good base keeps the slab from settling unevenly and helps with drainage.
3. Set the forms with a slope
Build forms from straight 2×4s on edge, staked every 3 ft or so on the outside, with the top edge at the finished height. Slope the patio away from the house, commonly about ⅛” to ¼” per foot. Screw the corners together and make sure the forms can’t move.
4. Place the reinforcement
Lay rebar in a grid and tie it at the crossings. Rest it on chairs so it sits near the middle of the slab, about 2” up in a 4” slab. Reinforcement lying on the gravel does almost nothing. Welded wire mesh is an alternative; it also needs supporting on chairs so it sits in the slab, not under it. See Rebar for a Concrete Slab for sizes and spacing.
5. The pour
Have help: at least two or three people for a patio this size. Dampen the base (no puddles) just before the concrete arrives.
- Place concrete into the forms, starting at the far end, and spread it with a rake or come-along. Don’t pour it in one spot and drag it a long way.
- Screed right away: pull a straight 2×4 across the top of the forms in a sawing motion to strike off the excess and fill low spots.
- Float with a bull float or a magnesium hand float to push down the stones and bring up a smooth layer of cream.
- Wait for the surface water (bleed water) to disappear. Finishing while it’s still wet weakens the surface.
- Edge and groove. Run an edging tool around the perimeter. Cut control joints with a groover about a quarter of the slab’s depth. For a 4” slab, joints are often spaced no more than about 8–10 ft apart, so this patio would get one joint across the middle.
- Finish with a broom drawn across the slab for a non-slip texture.
6. Cure it
Concrete gains strength slowly and needs moisture to do it. Keep the slab damp for about a week by misting it, covering it with plastic, or using a curing compound. Keep foot traffic off for a day or two and heavier loads off for longer. Avoid pouring when frost is expected or in very hot, windy weather. How Long Does Concrete Take to Cure? has the timings.
Common mistakes
- Adding water to make concrete easier to spread. It weakens the slab and causes cracking and dusting.
- Running short. A second batch hours later leaves a weak cold joint. Order 5–10% extra.
- No control joints. Concrete will crack; joints decide where.
- Reinforcement on the ground. It has to be in the slab, not under it.
Work out your own slab, footing or post holes in the Concrete Slab & Footing Planner.