It seems that UHU liquid glue, the kind that comes in a metal tube, stops working after about 10 to 13 years. It has become very liquid, and no longer has enough adhesiveness to even glue two pieces of paper together. Its cardboard box says "Produkt des Jahres 2004", so that gives me a rough idea of its age.
I hardly ever need paper glue, which is why it was so old.
I hardly ever need paper glue, which is why it was so old.