Lime Ash floors

There are two ways this can be done:

Natural white gypsum

or

Artificially produced gypsum/lime

Both are good solutions. The former is more expensive but could be required for provenance. The later has potential to go wrong with inexperienced installers who don't understand what they need to do or how to do it.

Neither are suitable for persistently damp applications such as cellar and basements but are good for suspended floors. 

I've recently discovered a form of red gypsum traditionally produced in Spain which is hydraulic and entirely suitable in damp locations. I'm looking to import this in the future when I open my shop.