Just to get it off my chest.... mixed up some SLC today, some from a
new pack, some from an old. D'oh. After mixing, it was pretty obvious
that the stuff wasn't going to self-level - it went on more like
plaster. Ho hum, I think, might as well chuck it down anyway. D'oh
number 2. Do a pretty good job of getting it smooth and reasonably
level, at least on the thick bits, which makes it worth it.

Wait four hours, and notice that it's a) sunk a bit in places, and b)
not really setting that well.

Scrape it all off, sweep up, and have cup of tea. I must not use old
powder. I must not use old powder.