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Alfred thumb Modern Straw-Clay Equipment: an incomplete history

An in-depth exploration of specific equipment design and process layout for manufacturing light straw-clay on the jobsite is a topic for a future article. Equipment will vary from simple hand tools to custom-made machinery, and with the size of the operation, whether do-it-yourselfer, one-off contractor, or the frequent-use (sub-)contractor. Equipment/tools do a number of jobs:

  • preparing subsoil
  • mixing subsoil with water to make slip
  • mixing straw with slip
  • delivering straw-clay to the wall
  • formwork

We'll start by showing some of the variety of straw-clay tumblers used in the USA in the last 2 decades to mix straw with clay slip.


Tumblers

inside early tumbler early tumbler motor
Alfred early tumbler

In the USA, New Mexico architect Alfred von Bachmayr delved deepest into perfecting the straw-clay tumbler. Here, one of his early designs stood on concrete blocks on the jobsite. It utilized two 55-gallon metal drums fastened end-to-end, supported by rubber wheels, and driven by a conventional electric motor through reduction pulleys. Simple, portable, quiet and as Alfred intended buildable by, say, a village welder with access to very common materials.

Alfred went on to make improvements in his designs. A number of builders own and operate his large trailer-mounted units made with 3-foot diameter plastic culvert rotated by a weatherproof irrigation boom drive-motor. Sadly, we lost Alfred in 2013.

Alfred's latest tumbler
 
We modified Alfred's tumbler with such improvements as a built-in, flip-down loading platform, and a pump and spray-wand system that can be calibrated to continuously deliver clay slip to the straw in exactly the correct amount for the particular job.
Our tumbler with wand and pump

Harmony tumbler Harmony tumbler
Harmony Homes of Traverse City, Michigan fabricated their own, very heavy-duty version of a tumbler out of an old steel tank, and mounted it on a double-axle trailer.

Processing subsoil

 

topsoil shredder

tilted screen
hydrocyclone
More to come:
Photos and description of advanced prototype equipment for making clay-rich clay slip, for low-density, high R-value light straw-clay

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