Tyvek + Cob?

Hi folks,

I'm building a somewhat typical stick framed tiny house, I want to try doing an earthen plaster on the interior face of the supporting walls- how will this effect what I sheathe those walls with externally?

I was planning on doing something typical, like untreated plywood with a tyvek layer, and then some cedar shingles. But does having the earthen plaster change this calculus? Do my walls need to "breathe"?

Thanks!
Matthew

I am sorry no one has been able to answer your question.

I have not worked with cob so I am just bumping this for more exposure.

Are you going to do drywall with cob as a plaster?

If so this might help:

https://permies.com/t/50336/Dale-cob-drywall-cabin

Hi Anne, good idea to bump it!

Hi Matthew.
I'm not an expert on cob (yet, I hope to change that) but I have a fairly good understanding of thermal building physics from my work background (engineer for renewable powers, worked in planning and designing buildings for 5 years).

I can't imagine why a cob plaster or clay plaster would change the outside of your wall. In general it's a good plaster that you can add instead of another plaster on any inside wall.

But the wall in general needs to work.
What do you plan as insulation? What is the plan for vapor retention? What climate are we talking? What's the use of the structure going to be?

For a better answer, could you give us the materials you're planning to use in order (e.g. from inside to outside)? Like:
1 inch Cob plaster
....
...
...
Plywood
Shingles

Hi Matthew,
I'm no building expert, but I like to read and learn from them. I second asking what the rest of your wall might be made out of.

One thing I would caution is mixing natural building with modern building methods. Modern building methods use materials that I don't like and make the air inside questionable, but they generally work to keep the weather out and the warmth/cold in. Natural building materials are great and can help with air quality and longevity of the building, and also do a great job keeping the weather out and the warmth/cold in.

But they work very differently. Natural building materials tend to be vapor permeable (or breathable as us lay people call it). Cob is vapor permeable and Tyvek is somewhat. It would probably be ok if you build the whole wall with permeability in mind, but whenever I have seen people try to mix permeability with sealing (i.e. natural vs modern) you end up with a mess.