Limecrete floor are a breathable alternative to solid concrete floors and have the advantage of containing insulation. They are made from LECA (Lightweight Expanded Clay Aggregate), which is a natural insulation product, and Natural Hydraulic Lime.
They are usually 4" (100mm) thick and can be either laid directly onto the earth or, if maximum insulation is desired, onto 6" (150mm) of loose LECA.
The limecrete floor can then be tiled onto directly or a lime mortar screed can be laid onto it before tiling. The latter would be required if underfloor heating was being installed on top of the limecrete.
Natural tiles such as limestone should be used to ensure that the new floor is breathable, and they should be laid onto a bed of lime mortar, and grouted with a lime grout.
Many old houses have unfortunately had concrete floors installed. These floors do not breath and can cause any residual ground moisture to spread up into the walls. A solution to this can be removing a strip of concrete and replacing it with limecrete - see Damp in Old Houses page.