Options for inbetween stone?

I'm in the beginning deign stages of getting  furnace up before winter this year, and one this I have in abundance is Field stone, and a lot of sandy/gravely land.   I have some ability to shape he stone as well.  What I'm wondering is what is the best 'mortaring' option to use between stones and the exhaust tube?  I could use concrete or mortar, but that makes it pretty much impossible to service/remove etc.. so I was thinking gravel/sand but from reading up regular old cob may be the easiest, and one of the best options to use.

C.D.

Hi Clyde,

I would use the dirt, or dirt enriched with some clay, or clay/sand mix if your dirt seems to not have any clay. In most cases you will find a pocket of good dirt for cob on a large property.

I think people have been using a clay slip (slurry) for bricks. It makes the bricks into a single thermal mass.

For field stone, I would guess that the irregular surfaces probably mean bigger gaps, requiring cob to bond them together thermally and stabilize them in place.

Slurry would only work if the joints were small, otherwise the high water contents of the slurry would cause cracking when drying.

Cristobal Cristo wrote:Hi Clyde,

I would use the dirt, or dirt enriched with some clay, or clay/sand mix if your dirt seems to not have any clay. In most cases you will find a pocket of good dirt for cob on a large property.

There is clay in some spots, but you have to dig down a few feet - I recently put up 1500 feet of field fence and dug a lot of 4 foot post holes so I have a pretty good idea of what is around.  -Very- Sandy.  In fact, the back part of the property was used by a previous owner to mine and sell sand.  Clay is easy enough to get, however, and mix in.

CD

Clyde, I can't claim to be a mass heater expert, but from what I've seen (based on the clay I can get, and they aren't all the same) you are absolutely on the right track. The key is a contiguous thermal bridge that makes one single mass.

Hi Clyde,

Welcome to Permies.