My Experience and Opinion on Adhesive Expiration Dates
Was the product stored in a cool dry place, does it have a manageable viscosity, and there is no separation of the solid or resin portion? If the answers are all yes, then it is good to use. When adhesives start to cure in the container, the viscosity increases until it becomes unmanageable and it looses many of its adhesive properties. Sikaflex cures as it reacts with moisture in the air. So, as long as it was stored properly, sealed against moisture, and has a manageable viscosity, then it is usable regardless of the expiration date stamped on the package. The rate of all chemical reactions are a function of time, activation energy, and temperature. Cooler temperatures equal longer work life. This is true for sikaflex and Proseal. I store sikaflex and unmixed Proseal in a freezer and use them whenever required. There is no scientific reason why an adhesive can be used for up to 12 months and then automatically becomes unusable after 12 months and one day. Expiration dates are arbitrary and typically arrived at without any test data. The main reason for the one year expiration date is that vendors decided that it is in their best interest to coerce their customers to throw away perfectly good adhesives and buy more stuff from them.
As an example, I worked in the electronics industry for 25 years as a Process Engineer and we stored many two component pre-mixed epoxies in the freezer prior to thawing out and applying. There was a one year expiration date on all our epoxies (sound familiar). I did a literature search and found a paper written by a NASA scientist who extrapolated out work life using the chemical activation energy and predicted that this type of epoxy when properly stored in the freezer would have a usable storage life of more than 1000 years. I sent a copy of this paper to the epoxy vendor and asked them to rethink and extend the one year expiration date. They weren't in the least bit interested in changing the expiration date. So in order to comply with ISO-9000 regulations, we changed our process instructions to state, "Frozen epoxies are usable for up to five years after the expiration date", and used the NASA paper as the reason for this decision. We completed extensive environmental testing of all products using these adhesives and we never had a problem with properly stored epoxies even when using them years past their expiration dates, and we saved a lot of money.