Cement-Bonded Particle Board for Partitions, Floors and Soffits

What the choice turns on

Cement-bonded particle board, usually shortened to CBPB, is chosen where a dry-built wall, floor or soffit has to survive conditions that would ruin gypsum or plywood: humidity, occasional wetting, impact, or exposure under a canopy. It is made from wood particles bound in Portland cement and pressed into dense, rigid sheets.

The misconception to avoid is that a "cement board" is one product. CBPB, fibre cement board and calcium silicate board are three different materials with different weights, fire test results and fixing rules. Swapping one for another on site because "it is all cement board" is how partitions end up cracked at joints, overweight on a mezzanine, or outside what the fire strategy assumed. Every one of those is found late, after finishes are on.

How it compares with other boards

For the full range of plasterboard options in dry office areas, see gypsum board types.

Where it is used

• Dry wall partitions in plant rooms, service corridors, warehouses, back of house and humid zones, usually on steel studs, where impact or moisture would damage gypsum
• Floor decking and underlay on steel mezzanines and raised platforms, and as a levelling layer under tiles or resilient flooring
• External soffits and canopy linings, protected from standing water, where the board is sealed and painted as the manufacturer directs
• Wet-area backing behind tiles, together with a waterproof membrane

The project's partition and ceiling design sits within false ceilings and partitions; choosing between a solid board wall and glazing is covered in glass partition vs drywall partition.

Moisture and fire behaviour

Moisture. The cement matrix protects the wood particles, so CBPB swells and loses strength far less than wood-based panels when damp. It still moves slightly with moisture and temperature, which is why joints are detailed to allow movement. It is not a waterproofing layer.

Fire. CBPB is much less combustible than resin-bonded boards, but it is not inert, because it contains wood. Its reaction-to-fire class is a property of the specific product as tested under EN 13501-1 or the test the manufacturer declares. The fire resistance of a partition or floor is a property of the whole tested system: board, studs, insulation, fixings and joints. What a particular wall, corridor or escape route requires is decided under NBC 2016 Part 4 by the fire consultant and the authority having jurisdiction.

Handling, cutting, fixing and joints

• Weight. Sheets are heavy. Plan lifting, two-person handling, and stud and track spacing to the manufacturer's tables; check mezzanine loads with the structural engineer
• Cutting. Carbide-tipped or diamond blades with dust extraction and dust masks, as the dust contains cement
• Fixing. Corrosion-resistant screws made for cement boards, pre-drilled near edges, at the manufacturer's spacing; stainless or coated fixings externally
• Joints. Either an expressed open joint, a cover strip, or a flexible sealant joint. Rigid filler over a butt joint usually cracks as the boards move
• Finishing. Primer suited to an alkaline cement surface before paint; tile adhesive suited to cement boards

Board thicknesses are typically chosen by use, thinner for linings and thicker for floors, and set from the manufacturer's data and the engineer's check.

Common mistakes

• CBPB substituted with another "cement board" without checking weight, fire test or fixing details.
• Rigid-filled joints that crack within months as the boards move.
• Drywall screws that strip, snap or rust.
• Used as waterproofing in a shower with no membrane behind the tiles.
• Mezzanine decking laid at the wrong span because the joist spacing was never checked against the board.
• Dry cutting indoors with no extraction, leaving cement dust through the services.

What to ask your contractor or supplier

• Is this cement-bonded particle board to IS 14276, or a different board?
• What is the tested reaction-to-fire class, and is the partition a tested system?
• What stud, joist or purlin spacing does the manufacturer allow for this thickness?
• How will joints be detailed, and which fixings are proposed?
• How will cutting dust be controlled on an occupied floor?

Standards referenced

Cement-bonded particle boards under IS 14276 and, in Europe, EN 634-2. Reaction-to-fire classification under EN 13501-1, with building requirements under NBC 2016 Part 4. Board thickness, spans, partition systems and fire performance for a particular project must be confirmed by the project's designer, structural engineer and fire consultant.