I've never heard of this used as the fiber, but it might work! It will really depend on the tensile strength of the cattails, and its shape. Do you have some dried cattail?

@N P It is a great video he made. I actually saved this one a few years back and used it this past Fall as instruction when I built my greenhouse.

@Mi Hi Yes, my kitchen will be a separate building in this case. I'll also be having an outdoor wood-fired bread oven, and an outdoor grill area.

There could be several different way to do it. I'd recommend just building the walls, putting the roof on, etc, and then installing the earthen floor inside afterwards. The earthen floor is just "floating" set inside the building, and doesn't need to have the walls attached to it. That's how I do them anyway. I'm installing and earthen floor right now on a project. I'll try to get some of the footage compiled and shared sometime soon.

Yes, but it will depend when in the drying process you remove the forms. You can take the forms off the newly packed cob after just a few days of drying, and it'll be easy to sculpt things into/onto the cob wall at that point. The only downside here is that you'll need to wait probably a few weeks for that layer to fully dry before putting the forms back on top to build the walls higher.

@Jessica Poe Yes, true! That would be an easier point to do the sculpting parts.

@Jessica Poe No, that's good! I use Type N mortar for my brick stemwalls too. Type S mortar is good, but N works just about the same. Are you putting concrete in the middle of your bricks like I do? If so, the vast majority of the cob wall weight will be on the concrete in the middle anyway. I don't think you have to worry about anything. It looks amazing! Thanks for sharing!