Which material is NOT recommended for use as a fire block?

The material that is not recommended for use as a fire block in this context is 35mm drywall. Fire blocks serve an important role in limiting the spread of fire within a building by providing a barrier that hinders the airflow and the migration of flames. While drywall is often used in various fire-rated applications due to its ability to delay flame spread and improve fire resistance, it typically needs to be specified in appropriate thicknesses and types for effective fire blocking.

In particular, the specified thickness of 35mm (which is just over 1.25 inches) is not a standard thickness for drywall used for fire blocking. Generally, fire blocking requires materials that possess certain fire-resistance ratings and standardized dimensions, such as those outlined for gypsum board that is used for fire wall systems. Other options like sheet metal, plywood or OSB, and the commonly specified thickness of gypsum board can withstand higher temperatures and meet building code requirements for fire blocking materials, making them more suitable than drywall of this particular dimension.

Choosing a material for fire blocking needs to take into account not only its fire resistance but also its commonly accepted dimensions and compatibility with other materials in assembly for fire-rated systems. Therefore, 35mm drywall does not fit the necessary criteria effectively.