How is the average bond strength of SFRM on primer determined?

The average bond strength of Spray-Applied Fire-Resistive Material (SFRM) on primer is determined to be a fraction of the bond strength on steel because SFRM is designed to adhere effectively to various surfaces, including primed steel substrates.

In fireproofing, the bond strength is critical for ensuring that the material remains intact and functions effectively during a fire scenario. Typically, the bond strength to a primer will not be as high as it is directly on steel, as the primer serves as an intermediary layer that may alter adhesion properties. Thus, specifying that the bond strength must be a fraction of the steel bond strength ensures that the SFRM will perform adequately without the expectation of achieving the same level of adherence.

Primers themselves can have different textures, compositions, and surface properties that affect how well the SFRM adheres. Therefore, establishing a specific fraction rather than expecting equal or higher bond strength reflects a realistic and safe approach to fireproofing practices. This ensures compliance with industry standards and helps in maintaining the integrity and performance of the fireproofing system.