no you dont need to use waterproofer but i would anyway, render is a protective finish and youll need plasticiser so a tub of waterproofer/plasticiser will set you back a grand sum of about 15 quid max..
quantities...ok, theres about 0.6 - 0.75m3 in a ton of sand
render goes on about 10-15mm thick if its pretty straight...
id say about 1/3rd of a ton of sand...
youll struggle to buy a third of a ton but you should be able to get 1/2 a ton at a smaller local builders merchant (not jewsons or the like cos they only wanna sell u ton bags or the little handy bags at £3 for 25kg), youll need a trailer or an empty ton bag, get em to dump the half ton in the ton bag and forklift it into the back of a medium/high roof panel van e.g transit...they wont wanna deliver 1/2 a ton but you might be lucky...
1/2 a ton should be around £15, dont get soft sand, get 'coarse building sand', sharp if you like but i prefer the stuff we get round here billed as 'building sand', the soft is norfolk...more like talc
4 bags of opc (ordinary portland cement) should do it...i a bit always get a bit more anyway...
if you want a good strong mix, nearly a full builders bucket of water (if the sands wet put less water in), 1/2 litre of waterproofer/plasticiser in a mixer, throw in half a bag of opc, 8 good shovels of sand, other half of opc, another 8 sand, should be nice and wet but not like curry, more like quicksand..thats about 3:1, youll need to take it off with a jackhammer...
throw in on in one coat, rule it off, let it firm up and float it.
it you wanna scratch it, do so..then top it in the morning still green
if you wanna add lime do that too, reduce cement accordingly...
this is for one side of said wall btw
it'll set very hard, light grey...
if you dont want/need it that hard, drop down to about a 5/6:1 and halve the waterproofer...it works on the cement content...
have you ever rendered a wall before? cos it aint as easy as it looks matey...