Which SFRM testing method uses polystyrene beads?

• A. The pull-off method
• B. The squeeze method
• C. The shear displacement method
• D. The displacement method

Answer: (D)

Displacement method is used to gauge sprayed fireproofing thickness by using a fixed, uniform marker—polystyrene beads—as a reference. The beads are placed on the surface or used under a calibrated cover plate, then the SFRM is applied. After curing, the coating height is read off the bead marker, or the amount of coating that covers or displaces the marker is measured. The beads provide a consistent, inert, and easy-to-handle reference that yields a quick and repeatable thickness reading in the field. Other testing approaches shown here focus on adhesion, squeeze behavior, or shear strength, and do not rely on a marker indicating thickness, which is why the displacement method specifically uses polystyrene beads.