Water tanks store rainwater from roofs. Tanks made of ferro-cement are fairly cheap, simple to make and easy to repair.
You do not need to use a lot of cement because of the wire reinforcement. The cement mortar can be as thin as 50mm.
1. This is what you will need:
2. Decide on the size of the tank. It should not be more than 1.5 metres high for your first try. Make a circle of the chosen diameter using a rope and 2 sticks.
3. Drive in wooden posts at 250mm intervals around the inside edge of your marked circle.
4. Mix up the mortar: 3 parts sand, 1 part cement, ¾ part water.
5. Spread 25mm of cement across the floor of the tank.
6. While the mortar is hardening, you must keep it damp – for several days if possible. Old sacks or matting can help keep it damp.
7. Lay 2 layers of wire mesh across the floor of the tank, between the poles. Leave at least 300mm of mesh to bend upwards.
8. Prepare the walls by winding at least two layers of mesh between the poles, spiralling upwards.
Make sure the holes are not exactly opposite each other. Tie the mesh together with fine wire.
9. The mesh should be strengthened by winding around ordinary galvanised fencing wire.
Fix a pipe for the tap in place 100mm above the floor and another at ground level for a washout, which is normally kept plugged.
10. Begin plastering the tank walls with the mortar mix. This needs at least two people – one on the inside and one on the outside. They work together to stop the mortar falling through the mesh.
You must keep the cement damp and shaded. Drying too quickly will cause cracks.
11. Remove the poles carefully, fold down any loose mesh and plaster, finishing off with a coat for the floor.
Keep it damp for at least two weeks before filling.
12. At first fill the tank very slowly. Cover the tank with a roof to keep out dirt and insects.
Congratulations! Let us know how you got on!
REPAIRS
If any cracks appear, empty the tank, chip away on each side of the crack and replaster. Again, keep it damp for 2 weeks.