Calcium Silicate Board for Fire and Wet Areas

Calcium silicate board is a homogeneous mineral board of calcium silicate, cellulose fibre and fillers, autoclaved to a stable sheet with no paper facing and classed A1 non-combustible under EN 13501-1. Unlike gypsum board it does not degrade in damp conditions, which is why it is used in wet areas, shafts and fire-rated systems.

By Dhruv Agarwal · · 1 min read

What it is

A homogeneous mineral board of calcium silicate, cellulose fibre and fillers, autoclaved to a stable, non-combustible sheet with no paper facing.

Specification at a glance

PropertyTypical specification
Fire classA1, non-combustible, to EN 13501-1
Density800 — 1,200 kg/m³ by grade
Thickness6mm — 20mm
Moisture behaviourDoes not degrade; dimensionally stable
FacingNone; homogeneous through thickness
FinishSkim, paint, or tile over

Where it belongs

ApplicationWhy
Shaft and duct enclosuresNon-combustible, tested systems available
Wet area tile substrateUnaffected by moisture
Fire-rated partitionsWhere A1 is specified
Plant rooms and high-temperature areasThermal stability
External soffits and canopiesWeather tolerance

Working with it

It is hard. Cutting produces silica dust and dulls standard blades quickly, so it needs carbide tooling, proper extraction and respiratory protection. Fixings need pre-drilling in the higher densities, and screws must be the right type or they will not seat flush.

None of this is difficult, but it is different from gypsum and site teams default to gypsum habits.

Where projects go wrong

  • Treated as waterproofing. The membrane is still required.
  • Cut without dust control. A genuine health issue, not a nuisance.
  • Specified everywhere when gypsum would serve, inflating cost.
  • Used outside a tested system and assumed to give a fire rating.
  • Standard drywall screws used, which do not perform in dense board.

Standards referenced

Reaction-to-fire classification to EN 13501-1. Fire and life safety provisions under NBC 2016, Part 4. Related flat sheet requirements under EN 12467.

Standards referenced

  • EN 13501-1 — Reaction to fire classification (CEN-CENELEC)
  • NBC 2016, Part 4 — Fire and life safety (Bureau of Indian Standards)
  • EN 12467 — Fibre-cement flat sheets (CEN-CENELEC)

Frequently asked

Gypsum board has a paper facing and a gypsum core; calcium silicate is a homogeneous mineral board with no paper. That means it does not degrade in damp conditions, does not support mould growth on a paper liner, and achieves A1 non-combustible classification rather than merely resisting fire for a period. It is heavier, harder to cut and considerably more expensive.

Permanently damp or wet areas, shaft and duct enclosures, high-temperature locations, and fire-rated systems where a non-combustible board is specified rather than a fire-resistant gypsum board. In ordinary dry office partitions gypsum is the appropriate and economical choice, and specifying calcium silicate throughout wastes money for no benefit.

Yes. The board does not deteriorate when wet, which is why it makes a sound substrate, but it is not a waterproofing layer. A shower or wet pantry still needs a tanking membrane applied over the board before tiling. Treating the board as the waterproofing is a common and expensive mistake that shows up as damp in adjacent rooms.

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