It’s a large project I’m involved in for a client, the limecrete is part of a refurbished on one wing of a mansion.
I think the best way forward would to gun up the existing non original concrete, do the reduce dig then get a specialist in to do supply and lay the gear.
It has somewhat fallen out of favour, because there is little need for the actual slab to be vapour permeable. The vapour permeability of NHL5 has also been questioned (see Hot Mixed Lime and Traditional Mortars: A Practical Guide to Their Use in Conservation and Repair by Nigel Copsey) due to its wide strength variability. You may as well use cement.
Glass foam aggregate is still useful to provide a capillary break and insulation. It is a bit tricky to compact.
So the build up is geotextile wrapped glass foam aggregate, DPM, concrete slab.
If there is no need for a capillary break the. I would revert to a normal compacted stone and insulation build up.
Your conservation architect will hate me. But really, vapour permeability in the floor just isn't needed.
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