Glad to hear you got it working after all -seemed such a waste not to be able to use it.
Again being a newbie here and not having gone through all the extensive discussions yet, I may be kicking in open doors, but I downloaded Ernie and Erica's plans and I don't see that issue of the joint between the metal barrel and cob/plasterwork being addressed plainly- there is a vermiculite expansion but it is further down if I got it right.
That barrel is going to expand and contract constantly and you're fighting a losing battle to try to fix the gap between the materials with plaster or other “hard” materials. Its probably not even be a great idea to fill the gap because it needs that space to expand when hot.
It wouldn't be a big job to remove a couple of inches of the- Ill call it stone work- and then wrap a strip of say foam rubber (or plastic) ¼ or ⅜” thick around the part of the barrel below the stonework and then fill the stonework back against the foam. After it has set you pull the foam out leaving a open joint between the materials that you fill with a high temperature fiber caulk- like this for example-
Its a lot of a over kill but its a great material- it resembles papier mache when its dry- but it stands up to very high temperatures. It also has the ability to be applied on a hot surface- like a repair on a running smelter etc
You fill that space with that caulk and it will seal it and take up the movements of the materials and if you slick it before its dry it will have the same appearance as plaster- dull white surface.
If you do lift the barrel you can deal with cracks inside with the same stuff.
Whats inside the stainless rising tube? Any pictures?
I do realize in reading here that there are various different schools of thought, concerning using “natural” materials vs man made (in lack of better words) and I respect the reasoning behind it, but Ive seen some less than great solutions to normal issues in dealing with high temperature applications. On the other hand Im learning a lot of things I haven't run into before- great fun!
James- What does one do you get a bad reputation here? Not read all the threads before posting???