Many photovoltaic (PV) technologies have been found to be sensitive to moisture that diffuses into a PV package. Even with the use of impermeable frontsheets and backsheets, moisture can penetrate from the edges of a module. To limit this moisture ingress pathway from occurring, manufacturers often use a low permeability polyisobutylene (PIB)‐based edge seal filled with desiccant to further restrict moisture ingress. Moisture ingress studies have shown that these materials are capable of blocking moisture for the 25‐year life of a module; but to do so, they must remain well‐adhered and free of cracks. This work investigates the potential use of a butt joint test for evaluating the long‐term durability of adhesion by looking for significant changes in the failure mode or quantitative value of a butt joint test. A round robin experiment was conducted using six different materials and two sample constructions, with and without effort to control edge pinch. Tests were evaluated looking at the strength of the bond, and the type of failure observed in a round robin test involving five laboratories. It was found that both the measured values, and the observed failure modes were repeatable and reproducible within at 95% confidence interval.