10.032 Adhesion/Cohesion of SFRM (Bond Strength of Fireproofing)

Q During a recent project, we found the Sprayed Fire-Resistive Material applied to the steel substrate to sound hollow upon surface tapping. The project specifications call ASTM E-736 Cohesion/Adhesion of Sprayed Fire-Resistive Material Applied to Structural Members as controlling the required bond strength. The old UBC Standard 7-6 and ASTM E-736 do not specify whether to cut to the substrate or not. My question is after setting the cap with epoxy and letting it set for approximately 24 hours, are we to cut around the cap to the substrate or are we to test it in-place without cutting around the cap?

— Steve Marcki, Construction Inspection Manager, Youngdahl Consulting Group, Inc.

A 9/07 – Response prepared by Terry Egland, a principal at Testing Engineers, Inc. and a registered engineer in California

The intent of ASTM Subcommittee E06.21 when writing E-736 was to outline a standard method to measure the combined bond strength from cohesion and adhesion of SFRM when applied to a structural member. Cutting around the cap down to the substrate will isolate the bond strength to only adhesion and may thereby indicate why your project sounds hollow but would not be a standard method to substantiate an unacceptable application of SFRM.

Since you suspect an improper application, it would be prudent to test the SFRM in the standard method and to also cut around the cap and test just for adhesiveness and report the findings to the design professional.

www.wordnet.princeton.edu/perl/webwn defines cohesion as the intermolecular force that holds together the molecules in a solid or liquid. They further define adhesion as the property of sticking together (as glue or wood) or the joining of surfaces of different composition.