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I dot and dabbed the wall with plasterboard then plastered. If you've got bare brick I'd imagine you'd do the same no? Can't plaster onto brick and internal rendering is a faff compared to boarding. I painted finished wall (once dry) with a mist coat and top coat of proper bathroom anti fungal paint, not that it'll ever hopefully see moisture.
Lustrolite cut well, I bought a dedicated fine tooth blade for the Festool and did a few practise runs to find the sweet settings and speeds, you can electric plane to finish but I found it came up just as nice with a block and some 400 grit paper.
When I did ours I followed the video advice of the brand Lustrolite, which is the Acrylic we ended up using anyway. Rubberised sealing paint behind any joins/edges then paint over with a colour similar to the panel so any slight glimpse through an edge will be less obvious. Think I might have a pic mid panel. And don't forget to use a neutral cure silicone.