Cement board

A cement board is a combination of cement and reinforcing fibers formed into 4 foot by 8 foot sheets (or 3 foot by 5 foot sheets), 1/4 to 1/2 inch thick that are typically used as a tile backing board. Cement board can be nailed or screwed to wood or steel studs to create a substrate for vertical tile and attached horizontally to plywood for tile floors, kitchen counters and backsplashes. It can be used on the exterior of buildings as a base for exterior plaster (stucco) systems and sometimes as the finish system itself.

Cement board adds impact resistance and strength to the wall surface as compared to water resistant gypsum boards. Cement board is also fabricated in thin sheets with polymer modified cements to allow bending for curved surfaces.

Cement boards are mainly cement bonded particle boards and cement fibre. Cement bonded particle boards have treated wood flakes as reinforcement, whereas in cement fibre boards have cellulose fibre, which is a plant extract as reinforcement. Cement acts as binder in both the cases. The fire resistance properties of cement bonded blue particle boards and cement fibre boards are the same. In terms of load-bearing capacity, cement-bonded particle boards have higher capacity than cement fibre boards. Cement particle boards can be manufactured from 6 mm to 40 mm thickness making it ideally suitable for high load bearing applications. These boards are made of a homogeneous mixture and hence are formed as single layer for any thickness. Cement fibre boards are more used in decorative applications and can be manufactured from 3 mm to 20 mm thickness. Fibre boards are made in very thin layers, making it extremely difficult to manufacture high thickness boards. Many manufacturers use additives like mica, aluminium stearate and cenospheres in order to achieve certain board qualities. Typical cement fiber board is made of approximately 40-60% of cement, 20-30% of fillers, 8-10% of cellulose, 10-15% of mica. Other additives like above mentioned aluminium stearate and PVA are normally used in quantities less than 1%. Cenospheres are used only in low density boards with quantities between 10-15%. The actual recipe depends on available raw materials and other local factors.

As a tile backing board, cement board has better long-term performance than paper-faced gypsum core products because it will not mildew or physically break down in the continued presence of moisture or leaks. Cement board is not actually waterproof, but it is highly resistant to absorbing moisture and has excellent drying properties. In areas continually exposed to water spray (i.e. showers) a waterproofing barrier is usually recommended behind the boards or as a trowel-applied product to the face of the boards behind the finish system.

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Wikipedia