Hello all we are installing a Burley Wakerley 12 to 18 kw wood burner in a our renovation project in the Massif Central in France. We had a Burlely Brampton 8 to 12 Kw in our previous French renovation and it was beyond amazing - crazy heat and efficiency!

The Burely will be installed in the existing fireplace (which we will refurbish) and will be room sealed with a tube on the rear of the stove going through the 600mm thick granite wall to the outside to draw in combustion air.

The stone walls are going to be internally rendered with a 60 to 80mm thick layer of hemp lime and then lime plaster. We may even in addition render externally with a layer of hemp lime. It depends on what the external stone work looks like once I have removed the cement render from the west facing gable end (a huge task).

I have attached a photo to show the current fireplace. I have removed some old (circa 1960's) concrete from around the large and extremely heavy granite slab which the current range its on. Underneath is a gravelly soil. I want to create a higher and level hearth for the Burley to sit on, probably coming up about 10cm from the current level. I don't plan to remove the existing hearth granite slab as it looks seriously heavy.

I wish to also extend the hearth outwards from the fireplace so the Burley can sit more into the room. Also we will be having a pine insulated wooden floor over the exisiting concrete block and beam floor so the extended tled hearth will protect the wooden floor from the Burley's serious heat output.

I have a few questions and I am looking for suggestions.

1.) What would be the best way to create a raised (10cm thick) insulated slab? My ideas was to tile over the slab with some nice rustic tiles for the Burley to sit on. I was thinking of putting 40mm of PIR/foam insulation and then 60mm of level concrete mix over the top to tile onto, creating the slab using wooden shuttering.

Do I need to put a DPC under the concrete slab/insulation and around the edges where it meets the rear stone wall and fireplace sides?

2.) Anyone have a better suggestion on how to do it? Maybe a limecrete slab without a DPC?

3.) Before rendering with hemp/lime mix what would you use to remove the soot staining from the stones on the rear of the fireplace? I know I will be applying hemp lime to the wall but I am worried about soot stains bleeding through the hemp lime. I have read there are various chemicals such as Trisodium phospate that could work...any thoughts?

Sorry it's not the best photo!!

<blockquote><cite>Posted By: tychwarel</cite>I wouldn't use PIR under concrete as it may well get hot enough to melt or even catch fire. why not make up a foam concrete step using thermalite blocks laid flat or pour a Leca or vermiculite concrete mix, Yes put a dpc under the lot</blockquote>

I like the idea of making an insulated slab to go under the stove. By my calculations the slab will be about 10cm deep by 1.5 metres deep and around 2 metres wide. This means I would need need 3 x 100 litre bags of vermiculite. It only costs €17.49 per bag so this is a good solution. Thanks for the suggestion.

Hi Peter. Thanks for the advice. I can probably go with a thicker slab but plan to use vermiculite concrete instead of insulation as suggested by Tychwarel. I think 15cm thick total will be okay. I would do a 10cm layer of vermiculite mixed with cement and then a 5cm sharp sand/fine gravel/cement screed over the top to tile onto. I will shutter the sides with timber at the front. What do you think?

There is no DPC under the granite stone walls. However at the front of the fireplace is an existing poured concrete floor this has a basic plastic sheeting DPC underneath it. There is also a small cave (cellar) under part of the floor and this is concrete block and beam.

I now have the materials to make my insulated hearth, which will be topped with a 25-30mm screed of cement and sand and then tiled over.

I have made a temporary frame work using timber on three sides to create the hearth with the rear stone wall of the fireplace creating the final side. The two legs (sides) of the fireplace which are granite slabs will sit inside the raised hearth.

At the shallowest part the 5.1 mix of vermiculite/cement slab will be 80mm thick. At the deepest part the slab will be just under 150mm thick. Over this I intend to put a 30mm screed of sharp sand and cement to help spread the load and protect the (imagine softer) vermiculite concrete.

My question is do I need to put reinforcing steel bar/grid in the vermiculite concrete layer? The area is approximately 140cm x 290cm.