Let's look at its various features and applications, its advantages and disadvantages of construction

Ferro-cement or ferrocement, also known as ferrocrete, is a composite building material named after iron (ferrum) and cement mortar. Unlike RCC (reinforced cement concrete), which uses thick steel reinforcement, ferro-cement employs multiple layers of galvanised metal wire mesh to attain the desired strength and resistance.

Although RCC construction is one of the most commonly practised techniques in our country, ferro-cement construction is superior in many applications because it is lightweight, allows architectural liberty in shape and design, is low maintenance and has a long lifespan. Ferro-cement can be constructed to achieve tensile strengths higher than RCC, making it one step ahead in crack-control and impact-resistance. Not only that, structural walls and slabs of ferro-cement can be cast in thicknesses as low as 25 millimetres, thereby cutting the use of building materials considerably. This is good both for the pocket and for the environment. Read on to get up close and personal with this emerging building material.

The basic mortar mixture that covers the wire mesh consists of sand and Portland cement in a 3:1 ratio. The absence of thick reinforcement and gravel results in relatively thinner structural building units that can be cast to make vaults, curves and other organic shapes.

Note: A typical ferro-cement application appears in the sloping roof structure of the house in the picture.

How are ferro-cement units made?

A uniform mesh or woven mat of thin (0.5–1.5 millimetre-thick) metal wires is laid throughout the cross-section of the unit, tied or welded to a skeleton of 3–8 millimetre-thick steel rods, which gives the unit its shape and strength. Then the mortar is trowelled by hand to fill the framed structure. Correct consistency and thorough penetration of the mortar is key for absolute curing (the process by which cement hardens, with adequate moisture and time) of the unit to achieve the expected robustness. The metal of the mesh must be completely covered in mortar to prevent corrosion.

Hexagonal, rectangular and expanded laths are a few types of wire mesh that are commonly used to reinforce the cement. Mechanised or semi-mechanised plastering techniques can be taken up as per the scale and demand of the structure to improve efficiency.

Where can ferro-cement be applied?

Apart from industrial, marine and agricultural applications, ferro-cement is emerging as a successful building and feature material for homes.

While slab foundations, walls, roof slabs, shell roofs, retaining walls in swimming pools, and those of rainwater-harvesting tanks, reservoirs and septic tanks are some structural applications, ferro-cement’s lightweight and flexible nature makes it a great solution for staircases (as in the picture), countertops, cupboards, built-in storage units, paving tiles, sculptures, urns, planters and so on.

• As with any kind of construction, it is necessary for a trained professional to make a careful structural analysis of the design before building commences to ensure the strength and viability of the ferro-cement structure.

Advantages

• Small-scale, non-structural applications (such as countertops, staircase treads and paving slabs) that can dispense with steel rod reinforcement, can be made with this alternative. It makes them easier and quicker to construct.

• The composition of the cement mix can be adjusted to the application to improve particular features of ferro-cement, such as earthquake resistance, fire resistance, water resistance and more.

• Since the cement mix is drier than what is used for RCC construction, and is held by the inner iron mesh, the external casting framework is not needed, saving on costs.

• Precast or prefabricated ferro-cement units can be installed in much less time, leading to overall economic gains.

• Ferro-cement (both built-in and precast type) can be coupled with other construction techniques such as wood, steel and earth construction.

Disadvantages

• Improper mortar penetration can lead to corrosion of the metal in the mesh framework.
• Ferro-cement structures are vulnerable to punctures by pointed objects.
• A quick, air-tight and strong output requires an abundance of fairly skilled labour.
• Welding or tying of multiple wire mesh and reinforcement joints is a time-consuming job.

Some best practices in this regard

• Shotcrete or sprayed concrete technique involves projecting the mortar mix onto a surface with high velocity through a hose. This method, known as ‘guniting’, can be used to eliminate the chances of leaving air gaps while filling the mesh with mortar.

• Admixtures can be added to the mortar to maintain its consistency, improve workability, enhance resistance or add colour to the cement mix.
• Sand can be replaced with a lightweight fine aggregate (shale, slate, pumice and so on) to make the structure even lighter.
• The material of the wire mesh and the reinforcement can be altered to upgrade the flexibility and resistance of the structure as per the context of the application. For instance, replacing steel reinforcement rods with basalt ones (made of fine fibres of the rock mixed with resins, polymers and so on) can make the structure more tensile, lighter and corrosion-resistant.

• A coat of broken glass, rigid foam or polystyrene fibre can be added to counter cracks or improve insulation.

To sum up

Durability, versatility, indoor comfort, energy efficiency, affordability and design freedom are a few properties of ferro-cement construction that make it a great alternative to RCC construction for homes. Plus, it allows for changes and improvements in materials and technology, including computer modelling for analysis, to improve the performance of the structure and reduce labour requirements.

The Ferrocement Society of India is a pioneer in ferro-cement technology in India. It is constantly engaged in research, development and standardisation of this material and technique for the benefit of the industry. You can reach out to them for information, guidance and consultation regarding activities relating to ferro-cement technology.