"MM" wrote in message
...
Because when I happen to leave the application brush unwashed for an
hour, it's still usable, whereas when I yesterday glued a piece of
timber in place it started almost immediately to "grab".



It's just that when it is in a joint it is in contact with wood over a large
surface area .. and if your joints are any good very thinly ... dry wood
acts like a sponge and sucks out the water content ... quickly.

I usually dampen wood slightly when I glue (except with contact adhesive)