"Mike" wrote in :

Just for interest, if it does deteriorate, could anyone explain the
mechanism - it would ease the pain of shelling out for a new bag!

It absorbs moisture from the air and forms hard lumps. If it hasn't done
this I still wouldn't recommend building a house with it but for a fence
post go ahead. The worst it can do is refuse to set.

That's the problem - it does seem to refuse to set, but I wanted to find
out how long I need to wait.

It's been 24hrs and my test bit is still toffeeish, it wouldn't hold up a
post.

I guess that means it's knackered, but with an undated bag, and it looking
perfectly good, it's a bit hard for a muppet like me to tell.

mike