Cob building questions

Good evening,

I've been reading up on many different types of eco friendly building methods from stone masonry to timber framing and have come apon cob. Ideally I'd like to incorporate all different materials, but I believe initially cob would be the quickest way to get something up since we have so much clay and sand.

I've bought a 20 acre lot near Roanoke, VA, and want to get something up on it that's livable. I've read a lot into cob building (hand carved house), and it seems like one downside is that it's difficult to make large batches and large sections at once.

I've got an old dump truck and case 580c, does anyone think it would be feasible to use the 580c to mix the cob and compress it? Let's say I use the loader to mix the sand, clay, and straw, then load it into a large rectangular "container", compress it down with the backhoe, then move the entire 6x3x3ft block to the building site in the loader bucket. In some ways this seems like a mix between cob + ceb, and should speed up the process considerably, and shaping/trimming could be done afterwards. The blocks could have wetter cob mix applied between/under before putting a new block on the wall, similar to how you'd lay bricks.

Has anyone tried this? Any thoughts?

Hi David,
Cob is beautiful to work with and very low tech. But, as you say, slow.

I haven’t seen good examples of making cob mechanized. You want the mix thick enough to support its own weight. And that makes it too thick to use for example a concrete mixer.
More liquid also means more shrinkage.

What you’re describing sounds like a large version adobe? Make blocks in a frame, let them dry, then mortar them in?!
Sounds like an interesting idea. Worth exploring in my opinion. Adobe is usually left to dry though. So you would need quite a lot of frames to make significant progress.

Have you looked into rammed earth building? You basically put up boards as if pouring concrete and fill it with your mix of sand, gravel and clay. Then compact it into the frames.

Welcome to the forum.

I understand timber framing as this is what we built our house with.

I don't understand wanting to make cob blocks.  That sounds similar to using adobe except in large blocks.

To me the large block will need a lot of drying time to set up before you can do construction.  Similar to large concrete blocks which are heavy and cumbersome.

How heavy will these blocks be and can one person easily manage them?

To me the beauty of cob is that a person a just apply the mud to what they want to cover.

Thanks for the replies!

My thoughts were to make the blocks in a frame, then move them to the building area while they are still somewhat wet after compressing them with the backhoe. This way they can bond with other blocks & cob "mortar" easily, then dry together, and I can do a majority of the process quickly solo.

By creating 3x3x6ft blocks, the block shouldn't bulge under its own weight and should stay solid. Most resources I have read express that you can only build about 3ft tall with cob a day, else it wont harden enough for the next course, and will bulge out below. Moving the blocks won't be an issue, as they'll fit in the loader bucket and probably weigh around 3000-4500 lbs each.

I enjoy the thought process that most cob builders have, which is to construct an entire house off of local resources.

Being in the mountains in VA, I have an abundance of timber, stone, clay, sand, and lime. I have some creeks, streams, and lakes nearby.

Ideally, I want to build a timber frame house on a stone rubble foundation with stone walls and perhaps even hay bales for insulation.
I believe this practice structure would also provide good practice for solar and insulation requirements.
Being a novice with timber framing and stone masonry, I expect that process to take much much longer and to make many mistakes. I'll mill my own timber and collecting/quarrying rocks, which will be very time intensive.

Rammed earth building sounds pretty similar, this also seems to be the same as adobe blocks, but not completely drying the blocks prior to building. I'll have to look into those building methods as well!

I have built many adobe homes in Australia.
Adobe bricks can be laid when they are dry enough to be moved.
You need dry low humidity air to allow drying time.
I think your idea of 4500 lbs of cob would be the wrong direction to go.
What time frame are you looking at?
Why not build a practise workshop with timber stud framework for a start, add a cob extension etc,
What foundations are you planning to use?
Concrete, rubble?

I agree with John. I would recommend starting small to see how it flows - if you make a right mix, if it does not crack and if you like the result. A small shed would be a good starting project and the testing ground for mixes, mortars, plasters. In such a case you will find a lot of advice here. For 2 ton soil blocks you will be on your own, which does not preclude your success of course. When you develop the feel of material and the technique you will feel better at trying a bigger block approach, if you will still want to pursue it.

Good evening
You’ve got a solid plan Cob is a great material but working with large batches is always a challenge Using your Case 580C to mix and compress blocks sounds like a smart way to speed things up while keeping the natural benefits of cob
A few things to think about
Mixing The loader should handle blending fine but getting the right moisture balance is key Too dry and it won’t bind Too wet and it’ll be tough to transport
Compression Might give you denser blocks and speed up drying but test it out first to make sure they bond well when stacked
Transport Moving 6x3x3 blocks without cracking could be tricky Using wetter cob between layers should help them fuse together and keep the structure solid
Efficiency If this works you could get walls up much faster while still keeping cob’s durability and aesthetics
Haven’t seen this exact method used before but it’s worth trying If it holds up structurally you might have a great hybrid approach here
Let us know how it goes This could be a real step forward for cob construction