If the bond strength of SFRM on steel is 500 psf, what must the average bond strength on the primer meet?

The requirement for the average bond strength of the primer in relation to the bond strength of the Spray Fire-Resistant Material (SFRM) on steel is grounded in ensuring the effectiveness and reliability of the fireproofing system. In this case, if the bond strength of the SFRM on steel is 500 psf, the average bond strength of the primer must meet or exceed a specific percentage of that value to ensure adequate adhesion between the surfaces.

Choosing an average bond strength of 400 psf reflects a common industry practice where the primer's bond strength should be less than the SFRM's bond strength, typically aiming for approximately 80% of its value. This ensures a sufficient safety margin for effective performance, as it allows the SFRM to adequately bond to the primer, which in turn should bond to the substrate (in this case, steel).

This means that if the primer's bond strength is set too low, it could compromise the effectiveness of the entire fireproofing system. Therefore, 400 psf not only meets industry standards but also assures compliance with safety expectations.

The other options, while numerical, do not represent the necessary safety margin relative to the requirements dictated by the bond strength of the SFRM