What material is commonly used to fill the annular space around metallic pipes in firestop systems?

Mortar is commonly used to fill the annular space around metallic pipes in firestop systems due to its effectiveness in creating a barrier against fire and smoke. Mortar has excellent fire-resistance properties, which help to maintain the integrity of fire-rated walls and floors when penetrations are made for pipes or conduits. This material can effectively seal gaps, preventing the passage of flames and toxic gases during a fire, which is essential for life safety and compliance with building codes.

Concrete is typically too rigid and may not accommodate thermal expansion or contraction and movement in the pipes over time. Silicone sealant, while flexible and good at preventing moisture intrusion, does not provide sufficient fire resistance on its own. Foam, although it can be used in certain applications, usually lacks the durability and fire-resisting properties inherent to mortar. Therefore, mortar's combination of durability, fire resistance, and ability to accommodate movement in penetrations makes it the optimal choice in firestop applications.