What is the minimum allowable bond strength of Spray-Applied Fire-Resistive Material (SFRM) on the primer used beneath it?

The minimum allowable bond strength of Spray-Applied Fire-Resistive Material (SFRM) on the primer used beneath it is defined as being at least half the bond strength of the SFRM on steel. This requirement ensures that the fireproofing material adheres adequately to the primer and does not compromise its fire-resistive properties in the event of a fire.

By requiring the bond strength to be at least half of that on steel, it creates a balance where the system can be effective while recognizing that the primer may not provide as strong of an adhesion surface compared to steel substrates. This consideration allows for variations in application surfaces, as different materials can present different adhesion characteristics, and sets a practical standard that still upholds the integrity and functionality of fireproofing systems in protecting structural steel during a fire event.