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Backfilling a cast iron fireplace advice

Quite often here at Castfireplaces we get asked questions regarding installation and how to do things, we are fireplace retailers and know about the products we sell so can often give good advice.
Today by email we were contacted about back filling a fireplace,
“We bought a couple gallery cast iron gas fires from you a couple weeks back…just now in process of having installed so far looks lovely – thanks for the great service. However I have a general installation question….
I intend to back fill the void behind cast iron inset with a 1-5 mixture of cement and vermiculite, I have read somewhere that I need (?) an air gap between the vermiculite and the cast iron. Apparently one trick is to place some cardboard between cast iron and the mix – the cardboard is supposed to burn off leaving a gap – do you know if its recommended to leave a gap? I would have thought having a gap will reduce the ability of the vermiculite to remove heat via conduction / prevent cracking of the cast iron. But then with no gap would the iron be able to expand okay.”
So what is backfilling I hear you all ask it’s actually the process of filling the chamber behind the fireplace making sure it’s all filled with vermiculite and cement so the fire doesn’t heat the chamber behind and pushes all the heat forward.
It is an essential part of fireplace fitting and if not done correctly damage will occur to the cast iron back, the customer is right cement and vermiculite is tightly packed into the void with a thin piece of cardboard behind the cast back the reason for this you do not want the vermiculite mix sticking to the firebrick that can be replaced.
Once done it’s topped off so that any soot will fall into the fireplace and not sit behind it as it’s flammable.
So some good advice and our customer is correct in his knowledge and should have fireplace fitted that can be signed off by building controls.
We are here to help at Castfireplaces that why ordering a fireplace from us is another great choice.

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