Carpentry for Vocational Schools - A Teachers Handbook
 3. CONCRETE
 (introduction...) 3.1. Composition of concrete 3.2. Proportions for mixing concrete 3.3. Reinforcing concrete 3.4. Finishing concrete

### 3.2. Proportions for mixing concrete

Concrete mixes are designated by three numbers, in some cases there are only two numbers. The ratio describes the quantity relationship which is determined by the architect or engineer.

a) The ratio 1:2:4

- The ratio 1 : 2 : 4 is defined :

- 1 part cement
- 2 parts fine aggregate/sand
- 4 parts rough aggregate/stone or gravel

- For one cubic metre of 1 : 2 : 4 concrete uses the following:

- 8 Bags of cement
- 0.5m/3 of fine aggregate/ sand
- 1.0m/3 of coarse aggregate/gravel
- 200 litre of water

b) Different ratios

- 1:2:4 is used for foundations, footing, footpath, troughs, slab, wall, bottom of the septic tank, etc.

- 1:2:3 is used for the walls of a septic tank,

- 1:2:2 is used for the top of a septic tank,

- 1:4 is used for concrete blocks.