Butyl adhesives are widely used to bond elastomeric membranes. The res
ults of uniaxial tension tests and simple shear tests conducted on bul
k samples of butyl adhesives are presented in this paper. Butyl adhesi
ves were found to have a rate-sensitive mechanical response with very
low tensile and shear strengths. The stress-strain curves of the adhes
ive are characterized by an initial elastic response followed by a reg
ion of large plastic flow. A three-element viscoelastic model was used
to model the stress-strain behavior of the adhesive. The model effect
ively combines a viscous dashpot and a network spring to capture the p
lastic flow in the material after the initial yield. The parameters of
the model are calibrated to simulate a wide range of mechanical respo
nse of the adhesive.