[Cob] Cob in the cold, with bears

[Shawn King]

Hi Iona, I'm a cobber and instructor with Cob Cottage Company (CCC), and I
thought I might be helpful in providing info on balecob.  CCC has been
innovating and testing bale-cob hybrids for more than a decade and we have
learned a lot about techniques for construction and performance in use. I'm
going to include here a write-up that addresses some of your main questions
plus covers details often missed. Some of it may be obvious, if so, please
forgive.  I also have a copy of the balecob addendum to The Hand Sculpted
House.  It is large PDF and may be a burden to some folk on this list, so
if you are interested, I'll send it to you directly (and anyone else on
this list, just let me know). Please let me know if I can assist further,
thanks!

Best, Shawn

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Bale cob extended info:



Your foundation needs to be the width of the bales PLUS the width of the
cob you will add inside and out. If it isn’t, you wind up building heavy
cob by hanging it over air just stuck to the bales, which risks the cob
part of the wall falling off later. I am a fan of using whole bales because
I do not use chain saws and that is currently the only way I know of to cut
them.  Keep in mind that a wider foundation is much more work and
potentially much higher environmental impact than a narrow one, depending
on the materials you are using and how sensitive a site you are building
on. On top of your stem wall material (stone, urbanite, etc.) put a bond
beam of cob about 4 inches thick so you have something to stake the first
row of bales into.



You can bend bales a little bit to get a more natural curve in a wall.  Put
two blocks on the ground separated a little less than the length of a
bale.  Place the bale oriented strings on the sides on the blocks. Put you
knee in the middle of the bale on the top side and lean into it until it
gives a little. Be careful not to “pop” the bale by pushing too far or too
fast. I have built large/long three-string bales into a 12 foot wide circle
(interior diameter) by bending, running bond stacking, staking then cob
wedging (below) and gotten a very solid wall.



Use wooden stakes. Make your own with inch-thick strong and strait branches
cut to length and sharpened at one end.  Do not use bamboo, it tears up the
straw and splits when you are trying to pound the stake in. NEVER use any
type of metal stake (including rebar) because the metal will condense water
vapor inside the bales and rot them from the inside out.



Use cob to wedge staked bales together. No bales are perfect at the edges,
and builders compress them because if you don’t the imperfections that
allow small amounts of rocking movement when one bale is stacked on another
multiply as you go up, leading to a very unstable wall. Remember you are
not using cob as mortar, meaning do not add cob so that it goes between
bales all the way through the wall. Just pack cob into the seams between
bales, first horizontal then vertical, of the already stacked and staked
bales you positioned so that they were in as close contact and as plumb and
level as you could get them. The seam filling sequence is outside
horizontal, inside horizontal, outside vertical, inside vertical. I like
sticky-sandy cob for this job, as the sand provides the compressive
strength in the wedging cob, while the stickiness helps it bond to the
straw. I’ll use a pinky-thick stick to sew the wedging cob into the straw
strands of the bale as much as I can.



Don’t worry about the wetness of the cob causing rot in your bales. Natural
builders in all sorts of wet climates have had no problems with this after
more than a decade of experimentation. The reason, I believe, is that the
water in even very wet cob is held by the cob and is not “free” to support
rot organisms in the straw the cob comes in contact with. The cob begins
drying immediately after application.



Connecting cob to straw bales: Straw resists application of earthen
materials by naturally interfering with adhesion. To get cob to bond to
straw, you need to start with a thin (1-2 inch) layer of wet, sticky cob.
Apply this liberally to the face of the bale, vigorously pushing the cob
into the straw with finger tips or a stick thin as your pinky or thinner.
You need to push the cob somewhat in between individual strands of straw in
the bale. To test connection, grab the applied cob with your finger tips
and pull towards you. If it peels right off, you need to work harder at
integrating.  If it resists pull away while still wet, it will be securely
attached when dry. Don’t expect the wet cob to be impossible to remove. You
will be able to pull it off, it should resist somewhat, not just peel away,
that’s all. You need to connect cob to this layer while the layer is still
wet, so go only partway up the wall with this material, meaning as far up
as you plan to build the same day, then add at least 3 inches of sandy cob
(interior). Build the sandy cob from the bottom of the wall (top of the
foundation stem wall) upwards, working it into the previously applied
sticky coat thoroughly with fingers or a stick as you go. This way the cob
is always supported by the foundation while you build. A common mistake is
for people to build cob “onto” a wall directly in lumps or layers rather
than “upward and onto” the wall from the bottom of the wall (top of the
foundation stem wall) as one thick layer blended with the sticky stuff you
added to the bales first.



How thick should the cob layer be?  On the inside, more means more mass to
store passive solar heat, but more mass is not always the best thing. More
than four or five inches in a northern climate is likely overkill since
passive solar input is limited by latitude. At less than 3 inches thick,
cob looses its structural integrity quickly as it gets thinner.  On the
outside of the building, probably 3 inches.  Cob for mass on the outside
can help a little with thermal performance, but I see its main advantage as
protection from animals that bore into materials to find cavities.  Many
insects, some birds, and some mammals actively seek hollow spaces and can
detect them through wood or earth. Straw bales “read” as hollows.  I have
seen birds and rodents peck or chew through exterior plasters and start
nesting inside bale walls. Several inches of cob on the outside of the wall
should greatly reduce or eliminate this problem by making the wall “read”
as solid instead of hollow.

On Fri, Apr 7, 2017 at 10:00 AM, Iona Fairlight Hawken <ionahawken at gmail.com
> wrote:

> Bill--
> Wow thank you for taking the time to write to me. I am trying to
> understand how the cob and bales connect. Do you plaster the cob into the
> bales or build the cob up from the ground the usual way? How does the cob
> connect to the bales? How thick is the cob in bale-cob?
>
> Would you consider sharing photos of the process of your bale-cob building
> so I can understand visually the connections and also the reciprocal roof?
>
> I want it to be round so that's perfect.
>
> Also, I love light but am wondering how to build a cob-bale house with
> lots of Windows (and without bears breaking them)...
>
> I never knew about a rocket mass heater! Looks ideal for a cold climate.
> What about radiant heating integrated into the whole house (and into the
> cob walls)? Does anyone do that?
>
> Best
> Iona
>
> > On Apr 4, 2017, at 12:56 PM, Bill Wright <bill at auburnacupuncture.net>
> wrote:
> >
> > Hi Iona,
> > If I were in your shoes I would also suggest, "bale-cob". Cut straw
> bales in 1/2 lengthwise, or use them whole. Use a cob straightening coat on
> the inside and the outside 2-3" thick over the bales. I would also suggest
> you make it round and make it as small as you can get away with. Bears
> won't be able to get thru bale-cob; not that I've had to test it ;^) but my
> building is bale-cob, and it's amazingly strong. I staked the bales
> together w/ 4' stakes, pinning each row to the one beneath it, and stacked
> like bricks.
> >
> > Again if it were me. . . I would put a reciprocal roof up first and
> build the walls in after that. Reciprocal roof w/ a living/earthen roof
> that is. Conversely, you could put the walls up, and put the reciprocal
> roof on them w/ a cable tension ring. Or if you have access to timbers,
> build your ring 1st out of timbers, and put the reciprocal roof on that. If
> you don't like the idea of bales, then I would suggest cordwood cob,
> especially if you want to do it during a short building season in the North
> Eastern US.
> >
> > Have you decided on a heat source? Have you considered a Rocket Mass
> Heater?
> >
> > Happy Building!
> > Bill
> >
> > Bill Wright, L.Ac., DNBAO
> > Wright Acupuncture and Massage
> > 251 Auburn Ravine Rd., Ste. #205
> > Auburn, CA 95603
> > 530-886-8927
> > "There is no path to healing, healing is the path"
> >
> >
> >> On Apr 3, 2017, at 7:13 PM, Iona Fairlight Hawken <ionahawken at gmail.com>
> wrote:
> >>
> >> Hi all--
> >> This has probably been covered before, but if I really want to build a
> cob house in a very cold area (like Maine), what are the options? Can I
> build a double cob wall with insulation (wool?) in between?
> >> Also, is cob vulnerable if a hungry bear is trying to enter? Or would
> it withstand a bear?
> >> Any advice would be greatly appreciated.
> >> Best, Iona
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