On most South African sites, concrete and mortar are batched by the bag and the wheelbarrow, not weighed. That works well as long as everyone uses the same barrow, fills it the same way and follows a known recipe. This guide sets out the recipes the Concrete Society of Southern Africa publishes, and how to use them so every batch comes out the same.
The barrow is your measuring jug
A builder’s wheelbarrow holds about 65 litres when filled level with the rim. Heaped barrows vary wildly, so fill to the rim and strike off the top. Keep one barrow for measuring sand and stone and don’t swap it halfway through the job. Cement is always measured in whole 50 kg bags.
Concrete
The Concrete Society’s 2024 leaflet gives three concrete mixes, each batched with two 50 kg bags of cement:
| Mix | Use | Per 2 bags of cement |
|---|---|---|
| Low strength | House foundations | 3½ barrows of concrete sand and 3½ barrows of stone |
| Medium strength | House floors, footpaths, driveways | 2½ barrows of sand and 2½ barrows of stone |
| High strength | Precast items, heavy-duty floors | 2 barrows of sand and 2 barrows of stone |
Use concrete sand and 19 mm or 26 mm stone. Per cubic metre of concrete, the same mixes need 290, 385 and 460 kg of cement respectively, which is how the cement, sand and stone calculator works out bags and cubes for any volume.
The leaflet also notes that these batches do not guarantee any particular strength. They are reliable mixes for ordinary house work. When your plans call for a strength in MPa, use ready-mix or a tested mix.
Mortar for brickwork
Mortar comes in classes. Class II is the normal mix for load-bearing walls in a house; Class I is stronger. Per 1,000 bricks, the Concrete Society gives:
| Mortar | Cement per 1,000 bricks | Building sand | Batch |
|---|---|---|---|
| Class II, common cement | 150 kg | 0.6 m³ | 2 bags : 6 barrows |
| Class II, masonry cement | 200 kg | 0.55 m³ | 2 bags : 4 barrows |
| Class I, common cement | 200 kg | 0.55 m³ | 2 bags : 4 barrows |
Corobrik describes a 1:6 cement and sand mix as Class II for normal load-bearing work. The mortar calculator scales these figures for maxi bricks and blocks.
Plaster
For 100 m² of plaster 15 mm thick, the Concrete Society gives 600 kg of common cement and about 2.3 m³ of plaster sand inside (2 bags to 6 barrows), and 700 kg and 2.25 m³ outside (2 bags to 5 barrows). External plaster is richer because it has to stand up to the weather. The plaster calculator scales this for other thicknesses.
Screed
AfriSam’s floor finishes guide gives a screed batch of one 50 kg bag of cement to two barrows (130 litres) of moist sand, which makes about 115 litres of compacted screed. Use concrete sand sieved through about 5 mm, not plaster sand. See the floor screed calculator.
Mixing well
- Mix on a board or steel plate, never on bare ground, which contaminates the mix and draws out water.
- Mix dry first. Turn the sand, stone and cement together until the colour is even, then add water a little at a time.
- Go easy on water. Add only enough to make the mix workable. Extra water makes concrete and mortar weaker and more likely to crack.
- Mix only what you can use. AfriSam suggests using a screed batch within about 45 minutes. Don’t add water to stiffening mortar to bring it back.
- Keep it the same. Same barrow, same fill, same bag count, every batch.
Why the barrow count matters
A batch that is short of cement looks fine on the day and fails later: dusty floors, crumbly mortar joints and plaster that sounds hollow. A batch with too much water is easier to work but weaker. Writing the recipe on a board where the mixer is set up, and checking the first few batches yourself, prevents most of these problems.
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.