What makes Gypsum plaster fire resistant?

Gypsum plaster is inherently fire resistant due to the unique properties of gypsum, the main component of the plaster. Gypsum is a naturally occurring mineral composed of hydrated calcium sulfate (CaSO4·2H2O).

When gypsum plaster is exposed to fire, several chemical reactions occur that contribute to its fire resistance:

  1. Dehydration: Gypsum contains a significant amount of water molecules chemically bound within its structure. When exposed to heat, this water is released in the form of steam. The process of water evaporation, or dehydration, absorbs a significant amount of heat energy, effectively cooling down the surrounding area and limiting the temperature rise.
  1. Endothermic Reaction: Gypsum undergoes an endothermic reaction during the process of dehydration. This means that as the water molecules are released, they absorb heat energy from the fire, further reducing the temperature of the plastered surface.
  1. Formation of Calcium Sulfate Hemihydrate: As gypsum dehydrates, it transforms into a different compound known as calcium sulfate hemihydrate (CaSO4·0.5H2O), commonly referred to as plaster of Paris. This transformation involves the recombination of calcium sulfate and water molecules. The resulting plaster of Paris acts as an insulating layer, creating a barrier between the fire and the underlying structure.

By absorbing heat, releasing water vapor, and forming an insulating layer, gypsum plaster effectively slows down the spread of fire and limits its damaging effects. It helps protect the underlying structure and provides valuable time for evacuation and firefighting measures.

It’s important to note that while gypsum plaster is fire resistant, it does have its limits. The duration and intensity of the fire, as well as other factors such as the thickness and application of the plaster, can affect its performance. In high-risk fire areas or for applications where enhanced fire protection is required, additional fire-resistant measures and materials may be necessary.

In summary, the unique properties of gypsum, including its ability to release water vapor, absorb heat energy, and form an insulating layer, contribute to the fire resistance of gypsum plaster.