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close this bookCarpentry for Vocational Schools - A Teachers Handbook
close this folder25. WATERTANKS
View the document(introduction...)
View the document25.1. Sizes of watertanks
View the document25.2. Watertank foundations
View the document25.3. Ferrocement tanks
View the document25.4. Maintenance and treatment of watertanks

25.3. Ferrocement tanks

An old corrugated iron tank which has rusted through can be used as the supporting frame for the ferrocement tank.

a) Preparation:

- When making a new concrete slab foundation, take out the lid and cut the bottom of the tank approximately 10 cm away from the wall.

Set the tank in the fresh concrete and cover the 10 cm bottom iron with fresh concrete.


- When setting the tank on an old concrete slab foundation, take out the lid and clean off the inside of the tank with wire brush and wash out.


b) Putting the wire mesh:

- Where the tank has a new foundation and the slab provides the bottom of the tank, a chicken wire mesh is laid inside and outside on the wall of the tank. For this punch holes all over the tank. The tie wire is passed through these holes to fasten the inner layer of chicken wire to the outside wire.

- Where the tank is placed on an old concrete slab , first lay of wire mesh on the bottom of the tank. Let the wire go up the wall about 15 cm and then lay the outside and inside wall and fasten them with the bottom layer.


c) Putting the cement mortar:

- The cement mortar must be made of fine sand and mixed with cement to a proportion of 2 parts sand to 1 part cement. The cement mortar should not be too wet.

- First, cement the bottom of the tank to a depth of about 50 mm. Check to see if the outlet to the tap is above this level. Let dry for 18 hours.

- The next step is to make a fairly dry mix and spread the mortar behind the wire mesh beginning at the bottom working up the wall.

Make sure all spaces between wall and wire mesh are filled properly.

- On reaching the top of the wall, start again from the bottom and cover the wire mesh with a second layer of cement mortar, working upwards in the same way.

- Use a steel or wooden float to smooth the mortar.


- When the inside is finished continue in the same way on the outside of the tank until the tank is covered and smoothed.

- After the mortar has dried for 24 hours, mix up cement and water in a bucket to form a paste-like cement wash. Use a brush to apply this cement wash on the inside and the outside of the tank in order to close all little holes still remaining in the wall and bottom of the ferrocement tank.


- The tank must be allowed to dry slowly. During this time keep it covered and every day water should be splashed over the tank. After two weeks, the tank can be half filled and two weeks later it can be filled to the top.

- Now the tank is strong enough to fit the lid. The lid can be made of a timber construction covered with flat iron provided with a hole to fit the strainer to catch the water from the gutter.

- Make sure all little spaces between lid and tank are closed with flywire to prevent mosquitoes from breeding inside the tank.