For years, Portland and gypsum cement-based plasters have been used to produce fire resistant walls. When we look at modern building codes, Portland and gypsum cement-based plasters are classified as non-combustible and are still used to construct fire-resistant wall assemblies. Advances in building practices and materials have forced the industry to develop new tools to ensure our modern high-performance buildings are safe.
Looking at the two chemistries, applied an identical way, to identical thicknesses, gypsum-based plasters typically provide greater fire protection than Portland cement-based plasters. A plethora of historic test results have led the industry to determine that, in general, both materials can be used to construct a one-hour fire-rated wall. While both chemistries can be used, the thickness varies. Gypsum-based plaster at 5/8-inch is sufficient to produce a one-hour fire-rated wall. Portland cement-based plaster needs to be 7/8-inch to achieve similar results.