More details of fiber cement board

Why use cement board?

The use of cement board in the construction industry is increasing due to its advantages over traditional building materials. A brief summary of the advantages and disadvantages are detailed below:

Advantages:

• Savings in cost, space, time, convenience,
• Environmentally-friendly,
• Highly-durable, impact-resistant,
• Resistant to fire, water, vermin and fungus.

Disadvantages:

• High initial cost,
• CBPB and FCB are around twice as heavy as gypsum-based board systems, so are expensive and awkward to transport and handle.

Significant savings can be gained through the use of cement board despite the initially higher cost when compared to gypsum wallboard due to its increased longevity.

Fibre Cement Board (FCB)

Fibre cement board (FCB) has been used since the 1900s when Ludwig Hatschek first combined 90% cement and 10% asbestos fibres with water. The mixture was run through a cardboard machine to produce asbestos cement board. This board was widely used for residential construction until the 1970s discovery that asbestos cement board causes mesothelioma (a rare form of lung cancer), at which time many countries strictly prohibited its use. FCB is not only the oldest type of cement board, but also the most widely used and produced. It is manufactured by 43 companies worldwide, 48% of cement board producers.

Fibre cement board consists of cement, water, silica, limestone flour and fibres, be they recycled, synthetic or cellulose pulp. Optional additives, including silica fume, metakaolin (Al₂Si₂O₅), fly ash, calcium silicate, flocculants (chemicals that promote coagulation) and defoamers may also be used.

The strength of FCB is dependent upon the composite fibres in several ways. Synthetic fibres such as Kevlar or carbon produce the strongest board, which is both moisture resistant and very expensive. Cellulose fibres can contain high levels of sugars and other organics that increase cement setting time and reduce the board's water resistance, although the use of kraft pulps, which release only very low amounts of sugar, can help to combat this. They can also contribute to an increased saturated mass, poor wet-to-dry dimensional stability and lower saturated strength, which can lead to freeze/thaw damage. The latter can, however, be controlled by approporiate board formulation. Recycled cellulose fibres are both environmentally friendly and economical, but are shorter than virgin fibres and as such produce weaker boards.

Fibre cement board is fire, moisture, impact and decay resistant and also lightweight, rendering it easy to handle and transport. It is also possible to print wood or brick effects directly onto it with a texture imitating plate, rendering it highly decorative. FCB is suitable for both internal and external applications, including weatherboard and façade, roofing, cladding, external and partition walls, underlay, flooring and tile-backing. Prefabricated housing projects using FCB can be seen in New Zealand,¹ Spain² and much of Africa,³ while in 2007 James Hardie constructed the Denny Park Appartments in Seattle, USA.⁴ The complexes are owned by the Low Income Housing Institute and are made from a combination of metal, Hardieplank and HardiePanel, which are sustainable FCB products with a 50 year guarantee.

There are three processing methods employed for the production of fibre cement board, namely the Hatscheck process, the Extrusion process and the Perlite process.

Hatschek process production of FCB

The most common production method used is the Hatschek process, during which unbleached cellulose fibres are re-pulped in water and then refined before being mixed with cement, silica and various additives. The mixture is deposited onto a wire substrate, vacuum de-watered and cured to form a cement board sheet. This air cured process is well suited to the production of roofing products and all applications where the sheets are directly exposed to harsh weather conditions. The main disadvantages of the Hatschek process are the large quantity of waste water produced and the fact that it can only produce fibre board in sheet form. Efforts to reduce the amount of water wasted have included installing filtration systems or adjusting the water pH for re-use.⁵

Extrusion process production of FCB

An alternative manufacturing method that enables the production of three-dimensional blocks of fibre cement with less wasted water is the Extrusion process, taken from the plastics industry. It involves forcing a highly viscous mixture through a shaped die. Achieving the right viscosity requires multiple additives, including binders, dispersants and surfactants, which increases the production cost.

Selected from: http://www.globalcement.com/magazine/articles/825-cement-boards-101