Tarmac technical services tell me that the Toplite blocks have no problem in handling heat so it looks like thermal expansion of the fire frame or the supporting lintel have caused the problem. I will report when all is solved.
Yes, this was a new build. I engaged a local woodburner centre to fit the fire and they visited the site on 3 occasions before actually fitting the fire to liaise with my builder. They insisted on about 600mm clearance above the fire so that they could use an adaptor to connect to a 9 inch...
Thanks Richard for picking up this problem. The chimney breast above the lintel over the top of the fire was blocked in with toplite blocks and rendered with two coats as you described. This was left for a fortnight before the vitcas was applied, a thickness of about 4 or 5 mm. The fire was...
I recently installed a Stovax Studio 1 Woodburner and after reading various posts and articles, rendered the chimney breast with a 5/1/1 mix and finished with a layer of Vitcas. Unfortunately cracks are appearing, including one which starts at the middle of the top edge of the frameles edge...