Cob: Re: Re: Cob + Strawbale + Earthships (fwd)

[David Knapp]

Tony,

The soil that is rammed into tires is relatively low moisture, something under 10% if I remember correctly.  The same soil works great in the rammed earth, earth bag technologies.  Cob in its best form has more moisture than that in order for it to be pliable enough to be hand molded into the wall.  If you where to try and squeeze a cob loaf into a tire, after the tire is nearly full, I'm afraid trying to push more into it to bulge the tire would simply not work.  Even though a piece of old cardboard or feedsack is used in the bottom to cover the hole in the tire, the cob would simply want to squeeze out the top when you tried to push more in.  If you used less moisture, it might help, but then you might as well stick to the normal rammed earth process.

Also, if you go to the trouble of installing posts to stabilize the tires, you may as well skip the tires to create a post & beam frame that you can cob/straw bale infill.

I'm all for mixing of natural building technologies to create our individual master pieces, but certain combinations become fruitless when blending them too much.  It's better to stay with a given technique and add too it without altering the original process too much (I'm all for anyone making a small backyard demo :-)

For example, we'll be building into a S-SW slope.  We are going to build the earthship shell (to take advantage of earth tempering via the berming) and use rammed earth, straw bale (end walls) and cob (as much as possible) for the utility room and bathroom wall partitions as much as possible.  I want to avoid all plywood and/or processed wood where a natural alternative exists as a better solution.  While the greenhouse sections will have sloped glass on the south facing sections, the kitchen section will have vertical glass (less glare and easier to control shades).  We moved the plan for the refrigerator to the other side of the hall about five feet to the north into the dining room U and am adding a small rammed earth partition so the winter sun hits that instead of the refrigerator.  When we start adobe filling the tire void, we will be finalizing where we plan to add several cob benches (mudroom, living room next to wood stove, etc).  In each case, the varied natural building techniques are all present and anyone showing up to help can jump right in on their individual expertise without much confusion.  Our earthship will be in the mountains at 8,700 feet, so we are doing everything to maximize our passive solar gain, large mass for earth berming for tempering our heating and cooling, and heavily insulating the ceiling (R-60 to R-100!).  We wanted a living roof to further help buffer temps, but we also want to catch clean rain fall so we had to go with a metal roof (Propanel) for our 10,000 gallon water cisterns.  Because this is a canyon with 12,000 foot mountains to the east and west, winter solstice (Dec. 22) only brings 3 hours of sunlight per day.  Another earthship close-by has worked out a deal to sell their excess PV generated electricity to the local utility in summer and buy it back at the same rate in winter when there is a short fall (they do have battery storage for grid outages).  I will negotiate with the utility to settle up on any excess once a year on April 1st to reduce income taxes (Ideally we want to produce 99.999% of what we use averaged over a year).

In order to get a building permit, the tires will have to be rammed with earth in the normal manner, else an engineer will not risk his reputation and career to sign off on the drawing.  As an alternative, you could build a demonstration wall that the code folks could monitor.  It'll cost a bit to get the engineering data needed to get them to buy into it.  My guess is that most folks building in natural building techniques would rather quietly slip between the cracks and not draw attention to themselves.  Since we are building in a planned subdivided sustainable community, we had to go with what the code officials would buy into without much fuss.

Dave

************************************************
David & Sheila Knapp
Winnebago, Illinois
Renewables at bigfoot.com
http://www.geocities.com/renewables/

"As you think, so shall you be!"
************************************************

----- Original Message ----- 
From: "Tony Glaser" <aglaser at engsoc.carleton.ca>
To: "David Knapp" <renewables at bigfoot.com>
Cc: <coblist at deatech.com>
Sent: Wednesday, January 12, 2000 3:34 PM
Subject: Cob: Re: Cob + Strawbale + Earthships (fwd)


> 
> Thanks for the info Dave. Maybe cob-enclosed-earth-filled tire walls would
> be thick enough to insulate well. Do you know how think they would be?
> Would I have to have cob on both sides of the tire-wall, or could the
> outside just be wrapped in chicken wire and plastered?
> 
> Another idea is to tie the tires together, as you say.  Then I could fill
> the tires with ONLY straw. I could put posts around the outer perimmeter
> of the tire-wall and cob on the inside. The posts and cob would be load
> bearing with their own foundations, while I imagine the
> insulating-straw-tire wall wouldn't need much of a foundation as it's not
> supporting anything and can move if it wants during the frost.
> 
> What do you think?
> 
> Tony
> 
> 
> 
> --------------------------------------------
> Anthony Glaser
> aglaser at engsoc.carleton.ca
> http://www.engsoc.carleton.ca/~aglaser
> Year 3 Electrical
> Faculty of Engineering, Carleton University
> 
> On Tue, 11 Jan 2000, David Knapp wrote:
> 
> > Tony,
> > 
> > Just be sure that you have a way of connecting the tires together.  Normally the tires and centers are compacted with 300 - 350 pounds of soil.  The tires bulge and interlock with each other.  It would be next to impossible to achieve this without filling and compacting the centers too.  Without it, you will have a wobbly, spongy wall.  Normally tire walls are round or U shaped as the individual case may be, but most are earth bermed.  Those that aren't are usually wrapped in a straw bale outer layer.  In my opinion, you'd be much better off to cob the wall and wrap it in straw bales (doing straw bale stucco on the outside).
> > 
> > Dave
> > 
> > ************************************************
> > David & Sheila Knapp
> > Winnebago, Illinois
> > Renewables at bigfoot.com
> > http://www.geocities.com/renewables/
> > 
> > "As you think, so shall you be!"
> > ************************************************
> > 
> > ----- Original Message ----- 
> > From: "Tony Glaser" <aglaser at engsoc.carleton.ca>
> > To: <coblist at deatech.com>
> > Sent: Tuesday, January 11, 2000 4:37 PM
> > Subject: Cob: Cob + Strawbale + Earthships (fwd)
> > 
> > 
> > > 
> > > 
> > > Hi folks,
> > > 
> > > Just looking for thoughts on my idea.  For those who don't know,
> > > earthships are a method of building using discarded car tires filled with
> > > earth and surrounded by concrete.  The tires are stacked like bricks
> > > and also serve as the foundation below grade. They are built in a 'U'
> > > shape with the opening of the 'U' facing south for passive solar.
> > > 
> > > I live in a cold climate and my idea is to fill the rims of the tires with
> > > dirt, the centers and gaps with straw, and cob both sides (more on the
> > > inside than out).
> > > 
> > > My goal is to find an architect and structural engineer in my province
> > > (Ontario) to get it working with and make the plans freely available.
> > > 
> > > What do you think?
> > > 
> > > Tony
> > > 
> > > --------------------------------------------
> > > Anthony Glaser
> > > aglaser at engsoc.carleton.ca
> > > http://www.engsoc.carleton.ca/~aglaser
> > > Year 3 Electrical
> > > Faculty of Engineering, Carleton University
> > > 
> > > 
> > > 
> > 
> 
>