Cob walls built against corrugated iron

Hi, I'm new to the cob world and know very little atm except that I'm going to love creating with it. My question is, can I use cob to line the inside of a steel framed corrugated iron shed 20'x20'x12' with a concrete floor. I know cob needs to breath and transfer moisture through the walls so I'm just seeking info on drawbacks.

From] https://www.greenhomebuilding.com/QandA/cob/structural.htm
Q: Can cob walls be built around steel beams?
     Do they work with steel in the same way concrete does?
     Is it possible to create a reinforced cob slab using formwork?
A: Steel is not as compatible with cob as it is with concrete.
   There is a greater discrepancy in the rates of expansion and contraction between the two materials, so cob with imbedded steel tends to break apart over time due to cracking.
   (The same happens with concrete and steel, but on a longer time scale.)

   It's much more effective to reinforce earthen materials with softer, lighter fibers such as straw and bamboo.
    Even so, I'd be surprised if you could get the same sort of strength out of cob that you can with concrete, either in compression or tension.
   But on the other hand, those sorts of strength are unnecessary for most aspects of small-scale construction."
   I would expect the same issue with cob against the sheet steel, differential expansion would cause the separation of the tow materials and crumbling of the cob."

Have you thought of a separate wall of cab, set apart from the steel?Create mud bricks and lay them inside the shed with an air gap between both?

What are you hoping to accomplish by lining this steel building with cob? Are you primarily looking for a natural interior esthetic? Are you looking for thermal mass to even out interior temperature from day to night? What sort of doors and windows are there, and what is the roof like?

I expect you would want to leave a small air gap between the cob and the iron walls, so that moisture could escape from the cob if necessary. As you are not looking for the cob to hold up anything but itself, you could make it considerably thinner than structural cob. I would not go less than about 6 inches, 8 would be better depending on height, and you would want some wing walls or buttresses at regular intervals or otherwise have the cob anchored against tipping over.

You could probably line corrugated steel with cob for thermal stability, yes. As Glenn said, structural or not, if you want it to be self supporting, you probably can't go much less than 6" -- and you probably can't go much more than that if you want it to be able to dry out with one side blocked against the steel. You might also consider using it as a plaster, but in that case, you will need some kind of lath for it to adhere to, because it certainly won't adhere directly to flat steel given their different expansion rates.

If you are aiming for self-supporting cob rather than a plaster on lath, do remember that it is going to dry faster on the exposed side than the covered side. This means you have to be careful not to build too quickly, or the differential rates of shrinkage will pull your wall out of plumb.

Good luck with this

Aside from allowing moisture to vent and not be trapped in the cob down the road, April is correct that having it tight to the steel on one side will interfere with good drying in construction. I would use some kind of slipform on the back, maybe a foot or so tall, that can be pulled up once a lift of cob stiffens up. Even a half inch of space will allow enough ventilation. It doesn't even need to be a totally continuous space; there can be spots every so often where the cob touches the metal as long as air can flow freely through most of the cavity.