I applied some silnet seam sealer to my tent. Its the right stuff. However it has not gone off at all. the only thing I can think of is the nozzle of the tube was blocked so I snipped off a corner and squeezed it out of there. Is there a catalyst in the top of the tube? Will applying some more properly let the first coat go off? any other ideas?

When you say it’s not gone off, is it still wet or just tacky?

still wet. completely unchanged from when it came out of the tube 18 hours agao

Something here.
Recommends using talc, after leaving the sealer to cure 24h.(Scroll down)
https://www.trailspace.com/articles/how-to-seam-seal-a-tent.html

From which decade/century does this seam sealer originate ?

Its not curing at all. Now 24 hours. Its a tube only a couple of years old

Does it have a use by date on it?

it finally went off! I guess then just the age of the tube but I threw it away so cannot check