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Hi The builder,
Thanks for the reply.
the existing finish is coloured textured stuff, we bought a tub a few years ago, and it comes out of the tub like ready mixed cement, and we used a paint roller to apply it to a cement/brick wall, so has a raised pattern, we saw some environment friendly timber framed housed being built a couple of years ago, and the plasterer/renderer finished the timber by applying some sort of coloured render with a trowel, then something like a large paint roller. this was onto wooden external board, and when finished it looked like a normal rendered coloured house.