Floating on thermal blocks - some q's

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Hi all, doing the stairwell wall - Celcon blocks- with sand and cement. I have done some floating before , mostly smaller walls though, and I have a few questions.

I understand that the maximum thickness i should do each coat is 11mm - but door casings etc mean i will be looking closer to 20mm - so two coats. I will also be doing the screed method - so laying on a few dots of plasterboard offcuts, then forming vertical screeds, before filling in the middles.

1) Do i do a backing coat of the whole wall of about 10mm, then form the screeds to be about 10mm on top of this scratch(?) coat? Or, do the screeds to be 20mm, then fill in in two coats in between? If i do a whole wall coat, it wont be flat (I'm not that good) but then obviously the screeds would take care of that for the second coat?

2) I'm not the quickest, so would it be a problem to form screeds, and fill in sections over a few days/evenings - so the screeds would be fully set when i rule off them. I realise this would be a join in the wall, but would this matter? This wouldn't be any different to patching in areas before a skim?

3) Does it matter how long i leave between the first and second coats? I'll be soaking the wall with water each time - so the render bonds to the high suction blocks.

Thanks
 
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