Thursday, October 30, 2008

Cob Spraying Day

It was a big day here at the cottage - Cob Spraying Day.  The straw bale walls have been waiting all year for their outside second coat.  The actual amount of spraying time was about five minutes.  The prep and cleanup took basically all day.  Redbeard showed up with two helpers and about sixty-one thousand dollars worth of equipment to do the job, including:
  • A tractor,
  • A PTO-driven cob-mixing vessel,
  • A peristaltic mud pump,
  • An air compressor the size of a chest freezer, and
  • Two Bobcats (one to load the mixer and one to load the mud pump)
He didn't actually get the entire cottage sprayed.  I'd say, maybe a fifth of it.  He concentrated on the east and west hard walls of the attached greenhouse (which needed their first coat of cob, and had been prepped with tar paper and chicken wire earlier in the summer.)  I dunno, it looked to me like the same number of people could have done as much in half the time if they'd just brought a wheelbarrow, a shovel, and a trowel instead.  I'd have to say it all went pretty smoothly though, I mean they knew what they were doing.  My contribution to the effort was basically to get my stuff out of the way, and to ask stupid questions.  I also lent them some tools, most of which I got back.

Let's watch the capital-intensive Kabuki.  One of Hunt Utilities Group's earlier development initiatives was around building printers.  It's pretty far back on the burner now, but they still have all this stuff around - might as well use it.  Gizmos are fun anyways, they make loud noises.

Screening the rocks out of the clay (very important.)

Wiring up "Huffpo", the mother of all 220v, 35cfm@100 psi air compressors.

Ms. Fancy, the Mixmeistress of Cob, supervises loading of the mixer.  There is some art to this - she explained later that she had a new/unfamiliar source of clay, which took a bit more time to get the mix right.  Incorrect proportions can cause sand to separate out in the hose and plug it solid.

Sprayable cob.  It has a consistency similar to Slurpee.  This is a special recipe with Enviro-seal (an earth stabilizer.)

Loading the pump:
Here's the nameplate on the peristaltic pump:

Next we have Redbeard in digital-camo bermudas, putting wand to wall:

Closeup of spraywand.  The peri pump controls the flow rate of mud.  The nozzle has about a 3/4 inch bore, on the inside of which is a ring of angled air jet holes.  Compressed air blasts the mud out the nozzle.  The operator has an air valve on the wand.

Troweling smooth:

Cleanup and more cleanup.  The mixer, the pump, the hose, basically everything the mud goes through has to be flushed out.

Again, what do I know, but it seems to me that in order to really justify this level of equipment you'd need to have straw bale cottages going by on a conveyor at the rate of four a day or something like that.

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