I’ve been looking through taginfo and it looks like building:material=plaster is the only widely-used tag for buildings covered with a render.
At least two other types of render are common in the UK:
‘tyrolean’ or pebble-dash: see Concrete Render on wikipedia. The surface is considerably more rugose than even a swirled plaster finish.
harling: a traditional finish for older buildings in Scotland (https://en.wikipedia.org/wiki/Harl). Usually completed with a lime-wash finish for waterproofing. I’m sure traditional buildings elsewhere in Britain have similar finishes. A good example of harled buildings is the harbour of Tobermory.
Obviously it is possible to tag these individually, but then there the values are less likely to be taken up by 3D building renderers. What I am wondering is whether we should perhaps introduce a more generic tag along the lines of building:material=render & then provide the additional detail with other tags. This should basically be treated as for building:material=plaster in the first instance (i.e., for default colours etc).
Any other thoughts?