In reply to Fraser:
I would do rough and ready experiments. But would start with 10 mm. 20 way too much.
It would help if the pattern you use doesn't press too deep. Say 2mm. If the render is clay-like at printing, you will get a good crisp imprint.
But you will need to learn stuff like how the render behaves on the wall. The top will dry before the bottom as the water falls by gravity. So do you render the bottom first? Then where do you start printing to take account of how the set progresses?
Maybe you render it very steadily, so you know which bit is going to set first, but then it's always warmer at the ceiling than the floor. So would be tempted to start at the top so you know that if you can keep in front of the set you are on a winner. And if the last row is crap it's not so visible at the bottom..
Also how long a time window do you have to print? So how many people with how many bits of wood. And how heavy a club do you need to hit it with, so you have the right tools.. You will need a saw and off cuts to do little fiddly bits.
If you do it and you start printing at the bottom say, as you approach the top I would texture the top few inches before you print it, because the last row is bound not to fit and that would save you having to cut planks to fit when it is going hard. You can free hand plank end marks in with a bolster.
Remember with render, if a patch is bad or you didn't get it all stamped before it went hard, you can scutch it off and redo it.
You will need to research getting the bond to work. Part of me says you want to needle gun the lot so you are dealing with clean brick and a good profile.
Do it when it's cold, you will have more time.
I can't overemphasise how physically demanding this work can be. Plastering is a walk in the park by comparison. If you decide SBR is the way to go, it is really claggy stuff that doesn't trowel flat easily, but moves with the trowel. If the crispness of planking is important to you this could be a stumbling block.
Experiment, experiment, experiment.
Post edited at 14:53