A Salutary Tale
Once upon a time, a few years ago when I took up paper model-making, I scoured the Internet for advice on the best glue to use. I wanted something that would cover well, dry relatively quickly and hold fast. There were various horror stories about water-based glues that caused shrinking and warping of the models, so I decided to avoid those.
Eventually, the consensus on the net seemed to be that this was the stuff to use:
Note that this is not a common or garden glue stick, as used frequently in primary schools around the world. Rather, this is a clear, thick, liquid glue pen that promises not to cause any problems with the paper or card being glued: no shrinkage, no ink smudges and no warping. It's a bit more expensive than many other glues, but it seemed that this was indeed the answer to my prayers.
For a while, I used this glue on all my paper models and it worked well. The joints were sound, colours never ran and the card was not distorted in any way. However, after a while, I noticed that my older models weren't quite as perfect as when I built them.
For example, the walls of my hotel started to sag. The fire escape fell off at one end (and was then torn off the other end by its own weight). It looked as if the glue had re-liquefied or softened, the parts had moved and then the glue had hardened again. What was going on?
Many of these models were stored on shelves high up in a back room. It gets pretty warm up there at times (hot air rises!) but is otherwise quite cool. Mind you, compared to some parts of the globe, the range of temperatures in my house is probably not that great. I can only imagine that such limited changes in temperature, perhaps aided by changes in humidity, had caused the glue to flow slightly over a long period.
It's a bit of a puzzle because any time that I've investigated, the (remaining) parts of each affected model have been held very firmly in place at whatever angle they've come to rest. At no point have I detected any stickiness or softening of the glue!
So, what next?
I gave up using the UHU office pens several years ago, once I started to notice this effect on my first card models. I'm sure that they are a very fine product for some applications, but they don't suit my needs at all. Now I use exclusively white glue (PVA, "Elmer's glue") for paper kits. I use a sculpting tool to spread a very thin layer on one part only; the join is relatively quick and absolutely permanent!
For the older models that suffered such fatigue, I've mostly had to bin them. The UHU glue has encrusted itself onto parts of the joints, leaving other previously-glued parts almost bare. It is possible to cut or scrape such hard conglomerations away and re-glue the models with PVA, but it's just not worth the effort in the worst cases. For the less badly affected kits (mostly vehicles), I have indeed made some such repairs.
At least with paper models, I can always build replacements. Of course, finding the time to do this might be a problem...