I have installed a wood/coal burning cast iron insert and mantlepiece and have filled the space behind the insert with hardcore. I have been told, in the interest of safety, to skim the top of the hardcore with fireproof cement. All I can find is 2kg tubs of fire cement from Wickes which I have used to do some repointing inside the fireplace. Although relatively inexpensive, I would need quite a few tubs to put a screed over the hardcore. Is there a fireproof cement that can be bought in larger quantities or is there something I can add to normal cement? If not can I render with a sharp sand/cement mix then skim over with the Wickes fire cement? I have visited most of the builders merchants and fireplace suppliers in Bedford but have been greeted with blank expressions.
Any advice would be greatly appreciated.