I can't attest to shelf life because I use so much of the stuff in my work, but I think Ralph is correct concerning it being inert after cure. I've also applied it without the water treatment to the opposite surface on a foam project last year because I couldn't get the water down into the narrow slot without flooding the area which would have been somewhat detrimantel, in my opinion at the time, and it still foamed up and cured okay, it just took longer to do so. I later had occasion to seperate and inspect that joint (don't ask) and the bond seemed strong. I've come to think that the water does two things - for hardwood, it causes the grain to expand, as we all know, therefore allowing greater penetration of the surface, and also reacts with the Gorilla to cause greater foaming/expansion. But - like Ralph, I'm willing to be wrong about this.
Will