# 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.

## 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

| Property | Typical specification |
| --- | --- |
| Fire class | A1, non-combustible, to EN 13501-1 |
| Density | 800 — 1,200 kg/m³ by grade |
| Thickness | 6mm — 20mm |
| Moisture behaviour | Does not degrade; dimensionally stable |
| Facing | None; homogeneous through thickness |
| Finish | Skim, paint, or tile over |

## Where it belongs

| Application | Why |
| --- | --- |
| Shaft and duct enclosures | Non-combustible, tested systems available |
| Wet area tile substrate | Unaffected by moisture |
| Fire-rated partitions | Where A1 is specified |
| Plant rooms and high-temperature areas | Thermal stability |
| External soffits and canopies | Weather 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**.

## Frequently asked questions

### How is it different from gypsum board?

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.

### Where is it worth the extra cost over gypsum?

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.

### Does it still need waterproofing in wet areas?

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.

## Sources

- [EN 13501-1](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Reaction to fire classification
- [NBC 2016, Part 4](https://www.bis.gov.in/standards/national-building-code/?lang=en) — Fire and life safety
- [EN 12467](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Fibre-cement flat sheets

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Source: https://hagerstone.com/materials/calcium-silicate-board