What type of fireproofing material expands when heated?

Intumescent coatings are designed to expand when exposed to high temperatures, such as those encountered during a fire. This expansion forms a thick, insulating char layer that protects the underlying structural element from the heat, effectively delaying the onset of structural failure. The ability to expand means that intumescent coatings can provide enhanced fire protection by increasing their volume and creating a barrier against heat.

In contrast, cementitious coatings and spray-applied cement do not have this characteristic. While they provide fire resistance, they do not change physically or expand when heated. Rigid board insulation also lacks the ability to expand and is primarily used for thermal resistance rather than fireproofing. Hence, the unique property of intumescent coatings makes them the correct choice in this context.