How to lay a concrete slab in backyard?

sammyla

What are the steps and material I need for a concrete slab in the backyard yard?  I had some quotes done and the trades that I have encountered don't use aggregate which I find odd. Is this a common practice not to use aggregate as part of the cement process?

JacobZ

Hi @sammyla,

When you say they don't use aggregate, is this in their concrete mix? Or as a base for the concrete slab?

Either way, aggregate in some form is necessary for the base and as part of the concrete mix.

Pouring a concrete slab starts with preparation. The site is marked out, soil is excavated to around 100–150 mm, and a compacted crushed rock base is laid, with compactible material such as drainage gravel or road base.

Formwork is then built around the slab area, followed by a vapour barrier and reinforcement mesh supported on reinforcing bar chairs.

Concrete is then poured, usually 100 mm thick for general use or 125–150 mm for driveways. A ready-mix of 20–25 MPa is standard. The surface is screeded, smoothed with a bull float, edges finished, and a broom finish applied for slip resistance.

If the quotes you have received do not include some allowance for base material, then I would suggest you ask them to include this in their quote, as it is an essential part of the process. 

If they are not using aggregate in the concrete itself, I would not consider their quote. Without aggregate, it is not concrete; it is mortar, which is not suitable for a slab.

Check out How To Pour A Small Concrete Slab for some further guidance.

Let me know if you have further questions.

Jacob