terry mate, the old apprentice is right, knows more than me bout this game.. 8)
anyway, slurry, just knock up a wet slurry/paste you can brush on with 50/50 sbr / water - add cement to desired consistency.. give your thermalites a wet down first to kill some of the suction, try and stay out of the sun at all times when your applying and the same with the rest.. almost impossible i know but try and time your day so you get the best of the shade where youre working..
let your slurry dry till next day..
4:1 sand / cement scratch with waterproofer.. use the correct amount per mixerfull (bout 1/2 litre or 3/4 of a mcdonanlds coffee cup ;D)
REALLY scratch it - plenty key...
leave it as long as you can but in this weather next day is gonna be fine...
the reason for this is so the waterproofer becomes active when the cement 'cures', then you'll have loads of time with your float coat to get a finish on it, youll prolly get the entire top half on before you have to touch it with the float, even in this heat..
theres some good experts on rendering on here mate.. i'd take their advise too... all depends on who's on...
top coat 5:1:1, no waterproofer technically but I i usually stick some in cos its a retarder too... there will be a good reason for not doing this so i'd listen to whatever gets posted on this subject..
just re-reading your last post... id get on it silly early in the morning before the sun gets too strong at the top... if the thermalites are up there too (i expect they will be) then the earlier the better mate.. you could try hanging a tarp off the back of the scaffold to keep the sun off it..
tell em they should have used concretes externally and try to cover yourself a bit in the event of it cracking... just tell em you'll do your best, hence the slurry..
o.. leave the slurry as rough as you possibly can for a key..