What is a fire protection plaster?
A fire protection plaster is a factory-made dry mix that is mixed with water and applied to steel or concrete by machine spraying or, less often, by hand with a trowel. Once set, it forms a monolithic layer usually between one and several centimetres thick. In US and international specifications, these materials are referred to as SFRM (spray-applied fire resistive materials) or cementitious fireproofing.
Plasters are one of the oldest and most proven types of fire protection. They involve no complex chemistry, cope well with high fire resistance ratings and easily “follow” complex geometry: connections, trusses, profiled decking.
Main types
Gypsum and gypsum-vermiculite plasters
Lightweight products with a gypsum binder, often containing vermiculite or other lightweight fillers. Gypsum contains chemically bound water, which evaporates in a fire and absorbs heat. These plasters are economical, quick to apply and widely used in commercial construction: offices, shopping centres, multi-storey frames. They are confined to dry interiors, often above a suspended ceiling.
Cement-vermiculite plasters
Portland cement-based products containing vermiculite. They are denser than gypsum plasters, moisture-resistant and can be used in unheated buildings and car parks, and some grades outdoors. Some materials in this group have been tested for hydrocarbon and even jet fires.
Dense cementitious plasters
Heavy-duty products for industry and oil and gas: pipe rack columns, vessel supports, vessel skirts. They withstand impact, firefighting water jets and weathering. Certain grades also protect steel against brittle fracture from cryogenic spills at LNG facilities.
How plaster works
The layer acts as a thermal barrier: its porous, low-conductivity structure slows down heating, while the bound water in the gypsum and the hardened cement paste absorbs heat as it evaporates. Until the water has been driven off, the temperature at the steel surface stays relatively low. On concrete, the plaster also protects the concrete cover against explosive spalling — a failure in which pieces of concrete “burst” off and expose the reinforcement.
How to choose
- Required fire resistance rating. Plasters are particularly cost-effective at R 90 – R 240, where paint thicknesses become large.
- Element type and massivity. The thickness is determined from the manufacturer’s tables, taking into account the reduced metal thickness (or section factor Hp/A) or, for concrete, the cover to the reinforcement.
- Fire scenario. Oil and gas applications require products approved for hydrocarbon fire and, where necessary, for jet fire.
- Environment. Gypsum products: dry interiors only; cementitious products: damp and unheated areas and, where the manufacturer permits, external use.
- Mechanical resistance and density. Areas with vehicle traffic require a dense product or additional protection.
- Primer and preparation. The manufacturer specifies acceptable primers; with an incompatible primer, reinforcing mesh or a bonding coat is required.
Application considerations
Plasters are sensitive to air and substrate temperature during application and setting — the permitted range is given in the technical data sheet. The thickness is built up in several passes and checked with a depth gauge. At high thicknesses and on elements subject to vibration, reinforcing mesh is used. External and oil and gas systems often include a sealing topcoat.
Common mistakes
- Gypsum plaster in an unheated warehouse or car park.
- Application over a primer not approved by the manufacturer, without mesh.
- Building up the full thickness in one heavy coat — resulting in cracking and delamination.
- Application in frost or heat outside the permitted range.
- No on-site checks of thickness and density.
- Damage during subsequent installation of building services that nobody makes good.
Materials from leading manufacturers
- CAFCO 300 / ISOLATEK Type 300 — Isolatek International — medium-density spray-applied gypsum fire protection for commercial buildings.
- PROMASPRAY-P300 — Promat — vermiculite-gypsum mix for steel, concrete and profiled steel decking inside buildings.
- Promat FENDOLITE MII — Promat — cement-vermiculite coating for hydrocarbon and jet fires.
- Pyrocrete 241 — Carboline — dense cementitious fire protection for oil and gas, including protection against cryogenic spills.
- Pyrocrete 239 — Carboline — medium-density cementitious fire protection for steel and concrete.
- Pyrocrete 241 HY, Pyrocrete 341 and Pyrocrete 40 — Carboline — cementitious fire protection for hydrocarbon and jet fires at oil and gas facilities.
- Pyrocrete 60 — Carboline — lightweight cementitious fire protection for steel and concrete, indoors and outdoors.
- Perlifoc, Perlifoc HP and Perlifoc HP Eco+ — Perlita y Vermiculita (Carboline) — gypsum-based plasters with perlite and vermiculite for steel, concrete and metal decks.
- Perlifoc T — Perlita y Vermiculita (Carboline) — cementitious plaster for the fire protection of concrete in tunnels.
- PROMASPRAY-F250 — Promat — lightweight dry-sprayed mineral fibre fire protection for steel, concrete and timber floors.
- CAFCO 400 / ISOLATEK Type 400 — Isolatek International — medium-density cementitious spray fireproofing for steel and concrete, up to 4 hours.
- CAFCO BLAZE-SHIELD II / ISOLATEK Type II — Isolatek International — dry-mix cementitious spray fireproofing for steel and concrete, up to 4 hours.
- CAFCO BLAZE-SHIELD HP / ISOLATEK Type HP — Isolatek International — medium-density cementitious spray fireproofing, up to 4 hours.
Frequently asked questions
Can plaster be left without a finish?
In many cases, yes, especially above a suspended ceiling. In exposed areas and outdoors a topcoat may be needed, as recommended by the manufacturer.
Is plaster suitable for concrete?
Yes, many products have solutions for upgrading the fire resistance of reinforced concrete slabs, beams and tunnel linings. The thickness is calculated from the concrete cover to the reinforcement and the required rating.
Why is vermiculite better than sand?
Vermiculite is light, heat-resistant and a good insulator. It makes the plaster lighter and, at the same thickness, a more effective protection than an ordinary cement-sand mortar.