Calcium Silicate Board for Fire and Wet Areas
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
| 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.
Standards referenced
- EN 13501-1 — Reaction to fire classification
- NBC 2016, Part 4 — Fire and life safety
- EN 12467 — Fibre-cement flat sheets