We render bathrooms to a tiling tolerance, not a painting tolerance. Different standard entirely.
Rendering to a tiling tolerance
A wall that is going to be painted can carry a few millimetres of variation and nobody will ever see it. A wall that is going to take 600 by 600 porcelain cannot. Large format tiles are rigid and they will telegraph every hollow and every bulge as an uneven joint line.
We work bathroom walls with a long straight edge and we check plumb and square at every corner, because a shower recess that is out of square shows up the moment the first row of tiles goes on.
Shower niches, hobs and the details
Formed niches are standard in Sydney bathrooms now and they are the fussiest part of the job. A niche needs square reveals, a slight fall on the base shelf so water drains out rather than sitting in it, and corners tight enough for the waterproofer to detail properly.
Hobs and step downs need the same attention. These are the points where waterproofing systems most commonly fail, and they fail because the render underneath gave the membrane a sharp edge or an unsupported corner to bridge.
Render is not waterproofing
Worth being direct about this because it comes up constantly. Cement render is not a waterproof membrane and no amount of it makes a wet area compliant.
In New South Wales, wet area waterproofing has to comply with AS 3740 and it has to be installed by a licensed waterproofer, who issues a certificate. The render is the substrate that the membrane goes onto. Our job is to give the waterproofer a surface that lets them do theirs properly.
Timing within a bathroom renovation
Render goes on after the plumbing and electrical rough in is complete and signed off, and after any wall framing or sheeting is finished. It goes on before waterproofing, screeding and tiling.
A single bathroom is usually one day on the tools plus curing time. We generally ask for a few days before the waterproofer comes in, because a membrane applied to render that is still green will have adhesion problems.