Example twin wall job: off top and out (article in progress 9 Oct 13)

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Silicone on floor to bed hearth slab onto (if slab sits okay then no particular need – this slate hearth rocked a little).  Alternatively place some felt or thin foam underneath. Hearth resting on carpet is perfect (no adhesive). Min hearth size 84cm x 84cm. Note that stove must be one that is certified not to heat downwards more than 100 degrees centigrade if you want to avoid having a 5″ thick constructional hearth.

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Pilot hole drilled through wall at 45 degrees (using long drill bit and spirit level with 45 bubble) then main hole knocked out using breaker drill. Cardboard to stop black twin wall being scratched (cardboard is to be removed).

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A 500mm length through a 10″ wall. Centre line assists keep everything on plan. Note that twin wall through wall is  500mm long and the wall is 10″ thick. In this instance we will fill the gap around the twin wall flue with Rockwall insulation (do NOT use standard loft insulation). One can make a rosette from Hardiebacker 6mm concrete board.

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Vitreous pipe is the narrower stuff at the bottom. Twin wall fatter because it is insulated. Note the self tappers. Pre-drill first as some vitreous surfaces can chip. Hardest part is getting the vertical lower section the exact correct height. If your hole through the wall is larger than required for the pipe then you have more room for error.

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Camera-shy apprentice


Black square is 12mm Hardiebacker board sprayed black with stove spray paint. Edges sealed with black Decorator’s Caulking or similar.

twin wall rosette outside

Twin wall rosette outside. You can make an internal rosette from the same Hardiebacker or the 6mm thick Hardiebacker (which can, if one is careful, be cut in the shape of a circle or oval).