Blog · Buying concrete
Should I mix my own concrete?
If you only need a small amount of concrete, mixing it yourself can look like the cheaper option. We compared mixing 2 m³ of C20 at home with having it mixed on site by one of our trucks.
The materials
Good concrete needs aggregate in every particle size, so the small pieces fill the gaps between the large ones. We use 0/4 washed sand and 4/20 limestone, which together cover everything from 0 to 20 mm.
From our own trials and calibration by Volumech Technical Services, one cubic metre of our C20 uses:
| Material | Per m³ |
|---|---|
| CEM I cement | 220 kg |
| 0/4 washed sand | 903 kg |
| 4/20 limestone | 1,009 kg |
| Water | 110 litres (water to cement ratio 0.5) |
The water to cement ratio matters more than most people think. Extra water makes the mix easier to work, but it weakens the concrete and makes cracking more likely. If you want a runnier mix, add cement or use a water-reducing admixture instead.
Finding 4/20 stone was the hard part. The builders’ merchants we checked stocked 10–20 mm gravel, which leaves a gap in the sizes below 10 mm, and a mix with that gap is weaker.
What it costs
Prices at the time of writing (15 April 2024), excluding VAT, for 2 m³:
| Option | What you’d buy | Total |
|---|---|---|
| Separate sand and gravel | 17.6 bags of cement, 2.12 bulk bags of sand, 2.3 bulk bags of aggregate | £424.15 |
| Ballast | 17.6 bags of cement, 4.5 bulk bags of ballast | £400.82 |
Those totals leave out the hidden costs: time spent collecting materials, rounding up to whole bulk bags, the water, wear on your tools, fuel or electricity, and mixer hire.
How long it takes
60 wheelbarrow loads
One of our trucks mixes about 1 m³ every two minutes, and the concrete goes in as fast as you can place it.
CEM I or CEM II
We priced the home mix with CEM I 52.5N cement. Switching to a cheaper CEM II bag saves around £78 on the materials, but it isn’t a like-for-like comparison: you need more CEM II to reach the same strength. What the cement types mean.
The verdict
- Home-mixed concrete is weaker unless the aggregates cover the full 0–20 mm range.
- Cheaper cement means a weaker mix for the same quantity.
- Bulk bags rarely work out to the exact amount, so you pay for surplus.
- Mixing 2 m³ by hand can take around five hours.
For most jobs, having it mixed on site saves time and effort, and you pay for the concrete that’s poured. For a current price, send us your details.