Light cob or cob-like options for a mobile building?

Hi Permies,
First post here. I'm thinking of creating a mobile sculpted tinyhouse and here is what I've brainstormed so far. The obvious problem I'm tackling here is that cob is far too heavy for an easily towable structure. I'm thinking I could create a coblike compound replacing some or all of the sand with sawdust, but I've been unable to find any info on the idea because I guess it hasn't been tried yet, didn't work, or just wasn't posted about. The other thought would be to make bottle walls and fill the bottles with sawdust instead of water or leave them empty, using cob in between as mortar to give the bottle walls their structure. The sawdust idea interests me the most as it would be very kind to work with and hopefully the resulting product would be light enough. Combining the two ideas, I could embed plastic bottles in the sawdust cob wall to further lighten it but again, I'm not sure what kinds of problems the sawdust will pose. I'm also open to other material ideas as long as they are green and very affordable.
Thanks in advance.

Hi Gabrielle,

Welcome to permies!

A sculpted tiny house on wheels is an interesting idea; I'm imagining all sorts of shapes moving down the road!

But I don't think your sawdust cob would work.

Besides the weight, I would imagine that any cob like material would not have the tension strength to put up with a bumpy ride, especially if there were bottles imbeded in it. I would think that most massive cob like materials should probably stay in place.

The only thing I can think of that MIGHT work is lightweight ferrocement, but even that might be a bit of a stretch.

Hopefully an experience builder will chime in.

My guess would be that for a tiny house frame construction of wood or metal would be the only viable options due to weight and strength issues. A tiny house should in theory be able to hold together even if it was stood upside down, while still being lightweight; I don't think any masonry type material can do this.