Hi all! I am renovating a stone barn and have removed the previous stone floor to install a limecrete slab above RFG with underfloor heating integrated in the slab. I was suggested to use lime with cork aggregate as per a St Astier product sheet (https://www.saint-astier.com/produits/beton-de-chaux-liege/) but was looking for some feedback from those with more experience on this idea. First, does it make sense to reduce thermal mass when I'm actually looking for that with UFH? The cork would help with thermal isolation from the ground but presumably store less heat. Second the StA sheet only mentions using cork aggregate 3-15mm and no sand/fines. Not sure if that makes sense from a durability perspective? I got in touch with mike wye to ask if they had thoughts but they had not heard of this lime/cork mix.

Thanks!

What U-value are looking to achieve ?

Re EPS/conventional solution - I'm aiming for a breathable floor so using the recycled foam glass and limecrete mtehod. How does that compare on performance and cost - I guess in short would be less performance to depth (if that's a metric ;P) ie it takes a thicker layer of rfg vs eps to get the same isolation. Why do you need metal reinforcement for UFH? do you mean for a placement grid? can use a 'geogrid' solution

Posted By: djh

FWIW, Mike Wye isn't listed as a distributor, so maybe try contacting one of those listed athttps://www.saint-astier.co.uk/#distributors" rel="nofollow" >https://www.saint-astier.co.uk/#distributors

yeah that's correct - but there is nothing proprietary about the St astier product sheet. It is nhl 5 lime and cork aggregate. The question is more general about anyone's experience or insight into this generic solution.

Posted By: enkidu

Posted By: djh

FWIW, Mike Wye isn't listed as a distributor, so maybe try contacting one of those listed at the web address I gave

yeah that's correct - but there is nothing proprietary about the St astier product sheet. It is nhl 5 lime and cork aggregate. The question is more general about anyone's experience or insight into this generic solution.

My point was that those companies listed as official distributors might be expected to know details of the products they sell and perhaps have experience of it.

Posted By: WillInAberdeenMaybe this mix is intended more for an unheated floor? It would certainly feel warmer than concrete under bare feet

Following the link above, it says that it's for use for 'dalle sur hérisson ou plancher bois'.

'Dalle sur hérisson' is literally a 'slab on a hedgehog', where a hedgehog is a French way of building up particular layers of stone to stop moisture reaching the slab by capillary action (not an actual hedgehog), while the lime product would presumably allow moisture vapour to escape through the slab. The second part - ou plancher bois - means 'or [on a] wooden floor'. Together, that implies that the product shouldn't be used where it may get damp.

The detailed product data also says it needs a screed over the top to distribute the imposed loads. I'd therefore imagine that anyone wanting UFCH would place it in the screed, not in the lightweight lime slab. And without UFCH it would be the cool screed underfoot, rather than the lightweight lime slab.

Posted By: WillInAberdeenAIUI cork is a more common building material in France and Spain where it grows

Yes, I do get the impression that lightweight cement-concretes are more common in France, incorporating EPS / expanded clay / other materials (including cork). I've seen mention of it as a solution to reducing the weight of a structure or the size of foundations, but guess it could be used for its improved thermal properties.

That may well be where this product comes in at ground-floor level - to add a little thermal insulation where you can't add EPS / XPS / a DPM due to needing to allow moisture vapour to escape.

Posted By: WillInAberdeenMaybe you'll get more feedback from a french-language building forum (Mike1 any suggestions?)

It's not a specialist green forum, but forumconstruire.com would be the first place to try. It has threads on lime slabs, but no idea if it mentions that product.

Sorry but what is RFG?

Thanks, Will. I'd somehow missed that. The RFG provides a capillary break as long as it's deep enough, so the slab should be dry. Probably needs a separation layer to stop the lime falling into it. But if it's providing the insulation, what's the point of the cork complication? Just adding weakness to the limecrete slab?

Posted By: enkiduCurrent thinking is to do the rfg 15cm compacted - lime/cork 10cm - lime/sand with ufh pipes 7cm. Hopefully best of all worlds ... ;)

Sounds OK to me, subject to checking the minimum thicknesses & other manufacturer's recommendations.

FWIW, RFG is a bear to compact.