Brick integrity

We recently inherited an enormous pile of antique brick from a turn of the century schoolhouse chimney tear-down. We were SO EXCITED, thinking, "Man, this is perfect for our RMH project!". Got the brick home, put together an RMH mockup in the driveway with the nicest bricks we could find in the pile, stoked up a super hot fire and let it rip for a couple hours. Once everything had cooled down, to our utter dismay, we discovered quite a few hairline cracks on the brick faces in the burn chamber. I read in the RMH manual by Ianto Evans that the old, soft, orange brick is often best for building an RMH, even when some of the bricks are broken, cracked, etc, they can still be used sometimes. So, are these bricks garbage? Or do we use them with the assumption that the cob and mortar are going to go a long way toward holding everything together? Input please.

Lauren - not sure about your area of the country, but I do know that in VA, most of the old bricks were not fired, but pressed and dried. When temps get up to a firing temp, they will split, crack and depending on the brick's mixture, can explode. If there's a local antique dealer or a reclaimer of old architectural items, give them a buzz.

Hi Lauren; You mite try poring a cast core instead of using brick on your fire box, then you can seal it over with cob, and use your brick to surround the whole thing. This is what I have done. The brick adds extra mass and It looks good to ! I use fire clay as the morter on the brick around the fire box and the horizontal transition area , then I switched to regular type s morter for the brick to surround the horizontal piping run . Type in cast core here on permies and the vidios of matts cast core and his cast chimney should come up, if not try broaudio on you tube. Good Luck Tom feel free to pm me if you have questions I can help with.