Ideas for making cob quicker?

Yesterday we made a 2 foot high wood form around the whole upright RMH. We cobed 2 feet high all around by dumping cob into the form. Making cob in wheel borrow was very slow going. Are there faster ways to do it. We used 4 bags of fire clay. The vertical tank is now cobed into place. thanks Alan

I've only ever done it the hard way (by foot), but I've read of people using:

-a plaster mixer (I don't remember the details, but plaster mixers work where normal cement mixers don't)

-a rototiller

-a Bobcat (or skid-steer)

-oxen or horses


That ought to at least set you Googling off in the right direction.

i used my mud mixer and drill. (im a drywaller) i made the clay very thin in a bucket then dumped it in the wheel barrow. then i used a hoe to mix in sand and straw/perlite. its still work no matter how you mix it. lol

We used a cement mixer for mud for many years. Around here you can rent one by the day, but we bought one because we built some large structures of low tech rammed earth, not cob, but very cob-like hand-rammed material.

You say you mixed it in a wheel barrow? Were you using hand tools to try and turn it - that would pretty much be the most knackering way to get it done.

* Lay a big plastic sheet on the ground.
* Add your ingredients to the sheet and start stomping on it in barefeet. Keep adding water slowly until you get the right consistency.
* grab the edge of the sheet and lift/pull so the cob rolls together.
* Decant to a barrow and move to your desired build site.

Generally cob building is done by treading because you can use much more of your weight and get a nice even mix. Cement mixers don't do so well I hear because the cob can ball up and roll around in lumps rather than squish into a nice cohesive mass.

Also, try to mix moderate portions at a time rather than massive amounts - it is quicker to get two small batches to the right mix and consistency than an oversized batch.

yes i mixed it in wheelbarrow. i didnt need enough to do the tarp thing. i have only made 2 cores to play with burning/testing. next step will be an outside bench by the fire pit. that will require the tarp. i will still mix the clay up in buckets first though. i really liked the consistency i had when whipped up good.

Something I heard about at my PDC in southern oregon, I think from Lary Korn but don't hold me to that. Someone who was doing large cob building projects in the Oregon area made a contraption out of a long corrugated steel culvert. They put long metal spikes in a spiral pattern down the inside of the culvert, so when you looked down the tube you would see all the spikes like teeth going down the inside. The culvert is then set up on powered rollers at an angle, so that one end is higher than the other end. So, into the higher end goes a repeating sequence of clay, sand, straw, clay, sand, straw... by the time it gets to the lower end of the tube the metal spikes have mixed it all into a nice consistent cob. This particular builder had a forklift with a bucket to collect the cob mix coming out of the end of the culvert, which was then lifted up to the top of some heavy duty plywood forms and pushed in. Once the cob was in the forms it was then stepped on with cober's thumb shoes, or wooden sandals with several dowels attached to the bottom.

Sorry that I do not have more detail about it, but that is the contraption as I remember it being relayed to me. It seems to me like it would work.

There's people using this type of mixer, i would think twin screws.

http://3.bp.blogspot.com/_Xs5cv5fbsh0/TQZkavv3QBI/AAAAAAAAAoY/itMTvrEBVnM/s1600/P1010748.JPG


Pic taken from this site.

http://permamax.blogspot.fr/p/overview-of-building-techniques-with.html

How bout diggin a ditch to sub soil and then filling it with your cob mix and then using one of these