Water tanks made of ferrocement are used widely in many parts of the world to store water for domestic, stock, irrigation and industrial purposes. Ferrocement (also called as Ferro-concrete) consists of a cement-rich mortar applied on both sides of a thin layer of wire mesh and closely spaced thin steel rods.
Advantages of Ferrocement
- Ferrocement component have high strength as the cement content is very high.
- Since steel is spread all over the area, we get a homogenous composition.
- Ferrocement is applied with pressure over the steel wire mesh matrix. The mortar holds in position because of the mechanical interlocking. Hence no shuttering is required to cast ferrocement components.
- The raw material required is readily available.
- Ferrocement can be fabricated into any desired shape.
- The cost of construction is low.
- No skilled labor is required to build ferrocement structures.
All these advantages make the application of ferrocement in construction industry vast. These advantages make it easy and affordable choice for building tanks.
Ferrocement tanks come in different sizes and shapes having different capacities.
Advantages of ferrocement tank over concrete tanks:
- They are usually cheaper to construct.
- They require less skilled labor.
- They can withstand shock better as ferrocement tanks are more flexible.
- Smaller tanks are portable.
Ferrocement tanks are built by hand troweling layers of cement mortar onto the wire frame. A tank may be resting on ground, underground or partially underground.
Methods of Construction of Ferrocement Tank
1. Building Tanks Without Formwork
In this method flexible mesh such as ‘chicken mesh’ is wrapped around stiff wire frame. A mason applies the first layer of mortar from one side of the tank while his assistant holds plastering float from the other side in the right place. This helps in compacting the mortar in its place without it falling through the mesh.
2. Building Tanks Using Temporary Formwork
In this method temporary formwork is placed on the inside of the tank during the application of the initial layer of mortar. The formwork is removed before plastering the inside surface of the tank. This temporary formwork can be wooden shuttering, flat or corrugated sheets of steel or coiled pipe.
3. Building Tanks Using Permanent Formwork
In this method the formwork is left in its place permanently. The tank is then plastered from outside and inside with the formwork in place supporting the wire mesh.
4. Centrally Produced Tank
Smaller ferrocement tanks can be centrally produced and transported as a whole to the place of its use. Larger tanks are produced in parts. Central production assures better quality control, but transportation cost may make the tanks less affordable.
The fittings that are usually built into the ferrocement tanks include:
- One or more taps for collecting water
- A drainage tap at the bottom of the tank. This tap is used to drain all the water when cleaning the tank
- An inlet pipe and
- An overflow pipe
Some Important Points of Consideration
The two material that make ferrocement tanks are – wire mesh and cement mortar. Careful selection of material and proper curing of cement mortar are very important to get good quality water tanks.
1. The Wire Mesh
Good distribution of wire mesh is very important to limit cracking in mortar. Wire meshes come in different types, diameters, stiffnesses and strengths. For larger tanks, larger diameter of wire (4mm and above) are welded at 100mm or 200mm spacing to form a square or rectangular grid. This provides a strong reinforcing frame. These grids are then covered with smaller sizes of mesh also called as ‘Chicken Mesh’.
Chicken mesh distributes the load through the mortar and into the larger diameter reinforcing wire. It can be easily moulded to form spherical surfaces.
2. The Cement Mortar
Cement Mortar is a mixture of sand, cement and water. The strength of mortar depends on the quality of the raw material, the mix ratio and workmanship.
Clean, dry and well graded sand should be used. Recently manufactured cement without lumps should be used. Water used for construction should be clean preferably drinking water quality.
The usual ratio of cement and dry sand is 1:3 by volume. The water cement ratio has an important effect on the final strength of the mortar. A ratio of about 0.4:1 to 0.5: 1 is ideal.
Due to its various advantages ferrocement tanks are being used for storing water for domestic use and for rainwater harvesting. Water stored in plastic tanks get heated up and hence it becomes difficult to use during summers. Water stored in ferrocement tanks remains comparatively cooler and hygienic.
Light weight, ease of construction and low cost of construction makes ferrocement tanks a popular choice in domestic and industrial sector.