Name:
Plaster or Render, something along those lines - that is, in case one of these terms is applicable.
Description:
So to first make sure what I am talking about, I mean basically the material houses nowadays are built with on the outside. The basic idea would revolve around a non-burnable material, possibly in different colours, to avoid building houses with wool just because there's no other way to give it any colour - very specific and probably not quite high on the priority list, but yeah, that's basically my suggestion.
Recipe:
Good question. Maybe some combination of sand or sandstone, water, maybe even a totally new material like lime or chalk (though that might be a bit too much effort - on the other hand that material could also be used otherwise then)
so probably something like this:
s=sand w=water bucket
s
w = 4x plaster
s