A more quantitative test for adhesion is the pull-off test where a loading fixture, commonly called a dolly or stub, is affixed by an adhesive to a sample of spray foam. By use of a portable pull-off adhesion tester, a load is increasingly applied to the surface until the dolly is pulled off. The force required to pull the dolly off or the force the dolly withstood, yields the tensile strength in pounds per square inch (psi) or mega Pascals (MPa). Failure will occur along the weakest plane within the system comprised of the dolly, adhesive, coating system, and substrate, and will be exposed by the fracture surface.
A field test is available to measure the compressive strength of spray applied polyurethane foam shortly after installation, allowing for appropriate curing time. To be widely accepted in the industry, this testing device and procedure must use proven testing technology; be simple and easy to use; be inexpensive; and be portable for use in the field. As called out in the ASTM application guide, the on-site testing device approximates ASTM D 1621 “Standard Test Method for Compressive Properties of Rigid Cellular Plastics”. The device must have repeatable results that can be correlated to data reported from laboratory testing.