Adhesion, cohesion, and bond testing
What E736 measures
ASTM E736 measures the tensile stress needed to pull SFRM away from the steel. A 2 in. diameter core is cut through the material to the substrate, a loading fixture is bonded to the surface, the adhesive is allowed to cure, and a calibrated pull-off device applies tension. The reported strength is load ÷ area, and the failure mode is recorded: cohesive (within the SFRM), adhesive (at the SFRM-steel interface), substrate, or adhesive/glue failure.
Acceptance
The project's approved design and the code set the minimum. A common IBC-referenced threshold is 150 psf for bond and cohesion, but verify the specification because some designs require more. A clean cohesive failure at a value above the minimum is generally acceptable; a glue or fixture failure is invalid and must be repeated. Low results often trace to oil, mill scale, dust, condensation, or the first pass drying too fast.
Worked example
A 2 in. core fails at 90 lb. Area = π(1.0)² = 3.14 in². Stress = 90 ÷ 3.14 = 28.7 psi; 28.7 × 144 = 4,130 psf. Failure is cohesive in the SFRM, well above 150 psf, so the test passes. If the same 90 lb had failed at the steel interface with a shiny substrate, the inspector would suspect surface contamination and require investigation, not automatic acceptance.
Traps
Not cutting through to the substrate; pulling before the adhesive cures; testing only thick, easy areas; ignoring failure mode; comparing psi and psf without converting.