To mortar or not to mortar, that is the question...

Whether 'tis Nobler in the mind to MORTAR
The CRACKS and GAPS of outrageous FIRE,
Or to take Arms against a Sea of CO2...

but seriously... I see mostly dry stacked fire brick. I like the idea of mortar to help level and seal. I'm wondering how an adobe-like mixture will perform, whether it would hold up. I'm talking clay / sand at about 1/3 clay to 2/3 sand ratio. It's local clay. I'm nervous about experimenting like this on the first one. I'd feel safer following a recipe. Is there a reason most people dry stack? Anybody tried building one with clay/sand mortar between the bricks, like traditional mortar but with clay/sand?

Another question... for the thermal mass, will recycled concrete rocks work? Someone told me certain types of rocks will crack or pop or sort of explode when heated. Is this an issue with the mass part of the system? I think not, but I wanted to ask.

Thanks guys!

Rando

Randy : Absolutley ! Check out Ianro Evans' Book 'Rocket Mass Heaters' - page 41 , Tips On Laying Brick - he says the brick will be stronger than the mortar, the mortar is to help level, fill gaps in chipped (recycled) brick ! Most every one i see Dry stacks the brick a couple of times to make sure they have the lay-out right , I think that a lot off pictures circulating around out there are these Trial fittings, I am sure there are more minimal motaring than true dry fit ! Y.M.M.V. , Pyro-maticly yours , g'Luck, Allen L.

Allen, thank you kindly for the reply. I have the book and have read most of it, but somehow I missed that page, I guess I better read it again more carefully. The description of the mortar work is good, I think it provides sufficient detail. It suggested mixing the mortar a bit wetter, "about the consistency of guacomole or custard" so it can be applied thin, just enough for leveling and filling tiny gaps, about 1/8 inch if possible (3 or 4 mm). --Randy