Cob Re: Carpet/cement per Pat

[Don Stephens]

With people innovating and sharing "It doesnt matter if we're all
sometimes wrong, there's bountiful reason for HOPE!"

Pat wrote

> I was at home depot(building supply store) and saw a 4x8 sheet of 
> fiberouse cement board (my name for it). I told myself, heck soak a 
> 4 x 8 piece of carpet and you'd have the same thing...a photo is at:
> http://www.gnat.net/~goshawk/losroom.htm ....

Great!  As I've indicated, the world is rapidly being buried in
used, abused and discarded carpet (along with paper, etc) and I'm always
thrilled to see someone come up with another way to see "waste" as
resource.  I want to cogitate a while on the possibilities...back later... 

> So in the house's case I will make the following changes:
> 
> 1. plaster both sides of the carpet.
> 2. use it only in the roof sections with good slope so no water sits.
>  
>    (the roof it's on now actuall has small "ponds" where the water 
> sits after a rain) (I realize that's wrong but this is a proto type 
> so I figure if it can work under the worst conditions...)
> 
> 3. add some kind of layer between two layers of carpet for 
> insulation in the roof. (clay straw (moisture problems?) earth (heavy 
> but good) etc)

Earth - not so good.  Earth is wonderful stuff and super in cob, rammed
earth, stucco, floors, thermal storage, growing stuff on your roof,
buffering short-term temerature fluctuations, etc., but as insulation,
it's heavy and only about R-.2 per inch (dry), eg.: a foot of earth is
less insulating than 1" of straw (~R-3).  Weight of a cubic foot of dry
earth ~ 120# dry - Weight of a square foot of compressed straw 1" deep " ~
8 ounces!  heavy = more structure = more effort and or expense!

> for a solid roof:
> top:  carpet/cement
> middle:  earth, clay straw etc (other ideas?)
> bottom: carpet/ cement....
> 
> I will be building both a dome roof and a shed roof with this 
> technique. For the dome roof I'm looking at building something like a 
> sweatlodge structure over the walls and then lay the carpet on that. 
> The shed roof will just be sitting on 2x4's or something. 
> That's my end of of the elephant....Pat

Your roof sandwich sounds like an interesting beginning!  The base layer
(on either temperary or permanant structural support) works.  The carpet/
cement cap layer sounds good too.  What seems to be needed is an
insulating filling that is high "R", low weight, environmentally kind,
cheap or free AND solid/monolithic.  If the bottom layer is strong in
compression and tension (carpet with enough concrete should be; it would
be even stronger with a layer of chicken wire imbeded in the concrete on
top of the carpet) and the top is also strong in compression and tension
(same coment as above), and if the filling of your sandwich is rigid,
monolithic and bonded to those top and bottom layers, then the whole thing
acts as a continuous beam.  If it's flat (as in your shed roof, or in a
wall) it has a structural behavior like a plywood/foam sandwich panel.  If
it's a dome, it is a shell structure and we know they are amazingly able
to transfer loads. (anybody doubting this can try crushing a egg, end to
end, between their palms!)

So what to put in the middle that sticks together, becomes rigid, provides
good insulation and doesn't weigh a ton?  First thoughts are fibrous
cement and cement/clay/straw.  (I am not a big fan of cement, when it
can
be avoided, because it's not very ecofriendly, but it has some
charactoristics that non-the-less make it endearing, used sparingly, in
certain applications.)  One of cement's special features is that it's
"hydronivorous" - it eats water to cure and will keep getting stronger
until it's run out of warer.  In a fibrous cement or cement/clay/straw
mix, I see that as meaning that it will keep absorbing moisture out of the
mix until it is well below the moisture level at which molds or other
natural decay can occur (10-15%).  

So if you made your bottom layer of carpet/cement (stuccoed on the bottom,
as you mentioned, to prevent moisture from reaching the backing), then did
a rather "dry" 8" to 15" middle layer (F/C or C/C/S) and let it set up,
then painted the bottom of your top carpet with a thick cream cement
coating before putting it in place on top of the sandwich, then capped it
with more cement (this carpet coating on both layers would be stronger,
less expensive and use less cement if mixed at least 50/50 with sand -
probably more like 30/70) and maybe some chicken wire, it should be
monolithic, hell-for-strong if your ratios were right and have an R-value
of 16 ro 30.  Before doing a real roof of this kind of experimental stuff,
it would make sense to try a few test sandwiches (with different mixes/
techniques)  about 4' x 4', let them cure a month, raise them off the
ground a little and then se how many folks can stand on top of them,
jumping up and down in rythm, before they fail (add a pail of beverage, a
little music and call it a party!)  And then, of course, report back to
the rest of us on the results....Don

PS:  Are you receptive to the idea of a "living Roof" surface on top? 
That's one of the techniques of which I'm particularly fond and one I've
been experimenting with since the 60s.  It's ecofriendly, cheap, gives an
almost eternal life to the waterproofing membrane underneath (no UV, no
freeze and thaw cycle, no dry and wet yoyo, no physical trama from foot
traffic or falling branches), manages run-off better and it's "purty".