The cement mortar water jar
Practical Action
To make the bottom of the tank, mark out a circle on the ground of 1m diameter and place ½
bricks or other suitable material around its circumference to act as a formwork.
Spread paper or plastic sheeting on the ground within the circle to stop the mortar sticking.
Mix a 1:3 cement: sand mortar and spread within the circle to a depth of 15mm.
When the bottom plate has set, place the sacking bag narrow end down on the plate and
begin filling it with sand, sawdust or rice husks. Make sure that the mortar base sticks out
from under the sack and tuck the edges of the sacking under the filling material, so that the
weight of the filling holds the sacking on the plate.
Fill the sack, fold the top and tie it closed. Then fold and smooth the sack into a regular
shape. Make a circular ring from wood or cement mortar and place this on top as the
formwork for the opening in the top of the jar.
Spray the sacking with water until it is thoroughly wet, then plaster on the first layer of
cement mortar to a thickness of up to 10mm.
Plaster on the second 5 - 7mm layer in the same manner as the first, checking the thickness
by pushing a nail in. Build up any thin spots.
Remove the sack and its contents 24hrs after the plastering is completed. Repair any defects
with mortar and paint the inside of the jar with cement slurry. Then cure the jar for 2 weeks
protecting it from sun and wind under damp sacking.
General information
This type of jar can be manufactured in any size. However, as the tank size gets bigger the mould
becomes unwieldy, and different methods have been devised for making the former. One such
example saw the construction of 1.8m3 jars using specially made curved bricks to construct the
formwork. The blocks are built into shape using mud as a temporary mortar and are then removed
once the tank is complete. The formwork can then be reused again and again.
In East Africa, the use of chicken mesh between the first and second coats of plaster is a
common addition which gives extra strength to the structure and helps prevent crack propagation.
This type of ferrocement tank can be loaded onto a truck for delivery, and therefore has the
advantage that it can be made centrally for later distribution. Watt, 1978, gives detailed
instructions for the construction of a 0.25m3 jar in ‘Ferrocement Water Tanks’. He suggests that
similar tanks can be built up to 4m3 in size. The smaller mortar jars replace the traditional
ceramic Thai jars and can be manufactured at about a tenth of the price. The quality of
workmanship for this type of jar should be of high standard, as any flaws in the jar can quickly
result in failure.
Material requirements
The quantities below are taken from a similar 1m3 jar used during a recent water and sanitation
programme in Tanzania. This tank had reinforcing and a tap and a washout fitted.
Materials
Cement (bag)
Unit price
(TSh) 1997 Prices
6,200
Chicken wire (roll)
25,000
Binding wire (kg)
900
G.I Pipe 1" (m)
2,000
G.I F-F connectors 1"
300
G.I. Elbows
185
Locking Tap 1"
2,500
G.I. Male plug 1"
800
(2100 TSh. = £1 Sterling at the time of writing)
Qty
2
0.25
0.50
1
2
2
1
1
Total
Cost
(TSh)
12,400
6,250
450
2,000
600
370
2,500
800
35,220
*sand and stone are not accounted for here as they were provided by the community as part of a self-help initiative.
** approximately 1 skilled and 1 unskilled person days are required per tank.
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