Sand, stone and soil are bought by volume in South Africa, and the unit everybody uses is the cube: one cubic metre. Most suppliers also sell half cubes. Getting the volume right is simple arithmetic, but ordering the wrong kind of sand, or forgetting that dug soil takes up more room than it did in the ground, causes more trouble than the sums. This guide covers both.
Cubes and half cubes
A cube is 1 m³, a box one metre each way. Suppliers sell sand and stone by the cube and the half cube (0.5 m³), so whatever volume you work out, round it up to the next half cube when you order. Smaller amounts come in bags at hardware stores, which suits patching and repairs.
Formula: volume (m³) = length × width × depth, all in metres. Then round up to the next 0.5 m³.
A load on a bakkie varies with the vehicle and the supplier, so ask how much they count as a load before comparing prices.
Which sand is which?
| Material | Used for |
|---|---|
| Concrete sand | Concrete, with stone and cement; screeds (sieved) |
| Building sand | Mortar for brickwork |
| Plaster sand | Plaster; also jointing sand for paving when completely dry |
| Washed river sand | Bedding sand under pavers |
| Stone, 19 mm or 26 mm | Concrete |
| Road base or crusher run | Bases under paving and driveways |
| Screened topsoil | Lawns, beds and levelling |
Keep the different sands in separate heaps on site. Building sand in concrete, or concrete sand in plaster, gives poor results that only show later.
How much for concrete, mortar and plaster?
For mixes, work from the cement, not the other way round. The Concrete Society of Southern Africa gives about 0.6 m³ each of concrete sand and stone per cubic metre of concrete, 0.6 m³ of building sand per 1,000 bricks for Class II mortar, and about 2.3 m³ of plaster sand per 100 m² of internal plaster at 15 mm. See concrete mixes by the wheelbarrow.
Spreading material over an area
For a layer of stone, sand or topsoil over a yard or bed, multiply the area by the depth. A 10 × 5 m area at 50 mm is 10 × 5 × 0.05 = 2.5 m³. Loose material settles and compacts once it is spread and walked on, so the BouWise calculators add an allowance (10% by default, which you can change) and round up to half cubes. The sand, gravel and topsoil calculators all work this way.
Digging out: swell and skips
Soil in the ground is packed tight. Once it is dug, it loosens and takes up more space, so a hole fills more skips than its own volume suggests. How much depends on the soil, its moisture and how it is dug, and published tables disagree a lot: dry sand alone is given anywhere from about 5% to 50%. So the excavation calculator asks for the swell your earthworks contractor or skip supplier uses for your ground.
South African skip hire companies commonly offer 3, 6 and 9 m³ skips, and larger 28 to 30 m³ bins for big jobs. Worked example: a 10 × 6 m area dug 0.6 m deep is 36 m³ in the ground. If your contractor allows 25% swell for that ground, 36 × 1.25 = 45 m³ comes out, which is 7.5, so 8 loads in 6 m³ skips.
Practical tips
- Strip and keep good topsoil before digging; it is worth reusing.
- Have deliveries tipped where they will be used, on a clean, hard surface or a sheet, so sand doesn’t mix with soil.
- Cover sand heaps in wind and rain.
- Check the skip’s rules on heavy material: soil and rubble are heavy, and some skips limit what you may put in them.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check SANS 10400 (the National Building Regulations) and your local municipality’s building control officer for your project.