Permsteading.com

I wouldn't sweat your soil too much. Especially if you're going to brick up the exterior anyway. What you've got will probably do just fine for fill!

It's not MADE of horse manure, it's merely covered in horse manure. Tell your wife that and see if it makes a difference

I think I might have hit a lucky streak. The weather warmed up enough that I could go dig some dirt and test for clay. My neighbor just had his ponds cleaned out. While most of my dirt is sandy with lots of slate I found a pile of pond cleanout that is grayish brown. From what I understand this sounds like free fire-clay to me so after some straining and draining I have a few pounds of what I believe to be fire-clay hanging to dry. So I am thinking I can use this free fire-clay and some wood ash and maybe something else as a binding agent to make a scaled down cast prototype for free. If it works I may even use it as an outdoor kitchen. Anyone try this before? If so what did you use for a bonding agent?

I've built lots of short lived cores with just found clay and sand, sometimes perlite, sometimes straw. I've never used a binder but I expect you could mix in a bit of furnace cement and it would set up fairly hard. I think it would be well worth doing, regardless of whether it lasts a few hours or a season.

The wood ash itself should make a good binder. It'll make the mix quite sticky.

Here's an interesting non-barrel RMH with metal cook surface. Counting the exhaust stack tubing there are several problems with the construction method and materials choices, in multiple areas, and an obvious lack of expansion joints between the "burner", decorative cob, steel cook surface (should be floating cast iron) and etc. But it might give you some ideas for doing one up right: