Ah - trouble is I've been spoiled by Ducatis :wink: ! (ducks and runs for cover - nothing worse than being trapped in an argument with a marque-mad biker!)
motorcycles aside........ my previous house had a similar set up in a bedroom.... rough 'forming' brickwork with lime/sand/hair over.... very friable. as permeability is not an issue here, i would go as far to say that a compo mortar - including (eek) sulphate resisting cement (apologies for the 'c' word) would be fine..... even - going on from previous post - a compo mix including an amount of vermiculite.... from my experience, the fire drew well once warmed..... best 'kick started' hee hee with some softwood kindling prior to coal.
p.s anyone seen the new b*w supermoto due in the spring of 2007?? yummy (soz evelyn : - ).............)