Cob email list

[Jon Hoyt]

>>From robtb  Mon Jun 30 17:43:22 1997
>From: "Robert Bolman" <robtb at efn.org>
>To: "Jon Hoyt" <jon at efn.org>
>Subject: Re: Cob email list
>Date: Tue, 1 Jul 1997 17:28:47 -0700
>X-MSMail-Priority: Normal
>X-Priority: 3
>MIME-Version: 1.0
>Status: RO
>
> Jon,
>Twice now I've been unable to post messages on the coblist.  They get stuck
>in my outbox and I'm constantly reminded that they're there until I delete
>them.  could you please post the following long post for me and/or let me
>know what I'm doing wrong.
>Thanks,
>-Rob
>
>Of Earth & Straw
>
>This is a long post upon the rough installation of a number of earthen
>elements in a post & beam straw bale structure that I'm building in Eugene,
>Oregon.  (everything is drying right now).  I hope that most of you will
>find something of interest here – indeed I will enjoy feedback on a number
>of concerns.
>
>In keeping with my concern over the poor distribution of the world's
>resources (as expressed on page 3 of the spring, '97 Last Straw), I want to
>incorporate as much earth into the structure as possible.  Presumable this
>will be in place of otherwise manufactured/purchased building materials.
>Therefore I've gone for earth plaster, earth floor and cob interior thermal
>mass details.
>
>Earth Plaster
>
>I started by taking chunks of the sticky, gooey clay that's so abundant
>just beneath the topsoil here, throwing them into small barrels and
>covering them with water.  After soaking for a while, I used a small,
>spear-like shovel to slice them into smaller pieces.  I then used a drywall
>mud mixer in an angle drill (I call it my egg beater) to whip it into what
>I'm calling clay slip.  I ultimately ran it through different coursenesses
>of screens to remove rocks and weeds.
>
>Mixing a couple ideas provided by Cedar Rose, I used a drywall texture gun
>to shoot a mixture of clay slip and wheat paste onto the bales.  This was
>meant to serve as an adhesive primer.  The idea is to get the first inch of
>straw to become hard thereby reducing the thickness of earth plaster
>necessary for a hard, non-resilient surface.  It was my first time with a
>drywall texture gun.  Not a fun job.  Next time I will consider using a
>thick nap roller or perhaps just my hands.
>
>The plaster performed above and beyond my expectations.  The recipe is as
>follows: Into a mortar mixer we dumped:
>2 buckets of clay slip
>7 buckets of sand
>1 bucket of chopped straw
>Water as needed
>
>The plaster troweled onto the wall just fine – even a very skeptical
>builder friend had to agree.  With only moderate frustration, I was able to
>get it to hang upside down above the windows and the door.  Only very minor
>cracking is seen here and there in the scratch coat.  Two weeks later, with
>the (very thick in some places) scratch coat dry, I was pleased to find
>that a sizable pile of the plaster wrapped carefully in a blue tarp was
>still perfectly usable.  I reconditioned it in a 5 gallon bucket with the
>egg beater.  I applied clay slip with a roller onto the scratch coat just
>before applying a second coat of plaster.  Upon drying, your thumbnail
>cannot separate the two coats at the edge.  I expect to finish the wall by
>slathering on a thin lime plaster (or perhaps a thick lime whitewash).
>This will be done as much for the white color as anything.  Do I need to
>know anything about adhesion between the earth and lime plasters?
>
>I'm convinced that we've been sold a bill of goods to believe that we need
>to buy plaster products that come from a factory in 50 Lb sacks on a pallet
>on the back of a truck.  My earth plaster has performed so well that I now
>feel emboldened to try to put it on the exterior of the straw bale walls.
>While I do live in rainy Eugene, Oregon, I have 30 inch eves, a good tall
>foundation (made of recycled concrete chunks) and I subscribe strongly to
>the "let it breath" school of thought.  I'm thinking of 1 or 2 applications
>of linseed oil on the exterior and 2 or 3 on the interior.  This is to make
>evaporation of water from the inside of the wall to the outside a little
>more likely and prompt than water vapor penetration from the interior of
>the house to the inside of the wall.  Any thoughtful response to the above
>reasoning will be very much listened to.  Also, any test data or approach
>for convincing my building department that an earth plaster on the exterior
>of a straw bale house in Western Oregon would be appreciated.
>
>Cob
>
>With all due respect to the time honored tradition of mixing cob with hands
>and feet (and hooves), I needed to get back to work (for income) ASAP.  So
>I went out and rented a bobcat.  It worked great!  As you know, a bobcat is
>a little tractor with a bucket up front and little balloon-like tires that
>can be made to turn in opposite directions causing the thing to literally
>spin around in one place.  I feel that this was perfect for mixing cob –
>the wheels relentlessly grinding the earth, sand and straw into the
>pavement, wrapping the clay around the grains of sand.  I was able to make
>a large automobile-sized mountain of cob in about 3 ½ hours.  I was able to
>form long sausage-like handfuls of cob able to swing and cantilever of
>their own strength and plasticity.  It is my good fortune to have a city
>lot on a quieter street.  If I didn't have a paved surface to work on, I
>don't think that it would have been as distinctly successful.
>
>Of the drawbacks, I was a little nervous about getting busted doing a
>questionable activity on a city street with out a clue – much less an
>erosion permit.  In my haste and in not being able to fully see the
>contents of the bucket while operating the machine, I didn't get enough
>sand into the mix.  The cracking has been more than I'm accustomed to
>seeing in cob.  This won't be a problem as all the cob details are waist
>height (and permitted) thermal mass walls and a (to be) heated cob bench.
>The cracks will fill in just fine.
>
>Earthen Floor
>
>About 2 ½ weeks after first mixing the cob which I had been keeping damp
>under a tarp, I rented a bobcat again to "recondition" and enlarge what was
>left of the pile.  I added more sand and a lot of chopped straw with the
>intent of using the same basic material for the floor.  Having turned to a
>number of different information sources and gotten just about as many
>entirely different approaches to doing an earthen floor, I decided to apply
>the cobish mix I had in one 4 inch, monolithic slab and trowel in control
>joints to (hopefully) absorb the cracking.  I didn't want to pour the
>thing,  but the mixture I had made was too stiff to effectively trowel
>smooth.  I ended up kneading the majority of material into place with feet,
>then immediately applying a mixture whipped wetter with my egg beater.
>That troweled fine and I have no concern about adhesion of the two layers
>given their similarity and that they went in at the same time.
>
>While the control joints have grown considerably, smaller cracks have also
>appeared in the field between.  I'm going to fill all cracks and joints
>with a very redish clay that came from elsewhere.  I'm told that to achieve
>the greatest contrast between my brown clay of the field and the red clay
>for the cracks, I should apply the first coat of linseed oil before filling
>the cracks and that that will prevent the red from bleeding into the brown.
> Anybody have experience with that?  In retrospect, the cracking being what
>it is and expecting the linseed oil to penetrate and thoroughly congeal
>about an inch, I would like to have gone with a much sandier mix – not
>unlike the plaster.
>
>I'm new and experimenting with all of this.  Your response to the above
>areas of concern will be very much appreciated.
>
>Also, THANK YOU VERY MUCH to the community of friends that helped with all
>the very laborous aspects of the work described above.
>
>We're calling the house "Mud Luscious".  If ever in Eugene, please visit
>the house at 1641 West Broadway.  At this time I'm having open houses every
>Sunday from 11:00 to 1:00
>
>Robert Bolman
>888 Almaden St, Eugene, OR 97402
>541-344-7196
>

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Jon Hoyt
Brice Consulting Services
(541) 686-8238
(541) 686-2096 FAX
jon at efn.org