Cob Off Topic: A Little Healthy Skepticism About FC

[M J Epko]

	(For those who pick this out of the archives somewhere down the road: FC
here means Fibrous Cement... not FerroCement, not Funky Chicken, not Fat
Chance, not Final Countdown.)

	Paul's praise for Mary is deserved. Let me add my gratitude as well. Keep
up the excellent stuff!

	FWIW, Joe Kennedy & I plan to visit McCain in the next few weeks. Earth
Quarterly, and the book, etc, are full of promise and exclamation points,
breathlessly excited and exciting; Joe & I both were intrigued and
open-mindedly dubious. (I guess maybe I'm the dubious party, actually.)

	Here's where I irk Paul by throwing out a bunch of questions and doubts
while having done absolutely nothing (yet) to find the answers myself.

	My first reaction to the "Build A House For $7 A Square Foot!" banner on
the magazine was skepticism... it's the sort of thing that people were (and
some still are) saying about strawbale. Even cob can have a tough time
clocking in at that price, once all of our modern conveniences and the
myriad miscellaneous expenses are thrown in. It's not impossible,
particularly in moderate climates, to build an *entire* house (not just the
shell) nicely for $7/sf or even less (witness Ianto, witness MacDonald,
witness countless scads of recycling and repurposing DIYers), but building
for that cost really has little to do with the material. Stick-framed
houses can be built for that... if the lumber and almost everything else is
reclaimed and recycled. Buying 2x4s from a lumberyard for a stick-framed
house is like buying brand-new magazines and newspapers to build a fibrous
cement house, or brand new tires to build an earthship. 

	McCain's recipe contains 60% saturated paper, 30% sand, and 10% cement.
Understandably then, fibrous cement (like cement-stabilized soil) is
admitted to be moisture intolerant - that it will take up moisture and fail
catastrophically because of it. The 1/10th cement part of the mixture can't
hold the other 9/10ths together under saturation conditions. What I don't
know is how long saturation conditions (under load, live and dead) need to
prevail before catastrophic failure. (Wood and straw, of course, and
virtually any organic/decomposable material, will also fail given sustained
periods of elevated moisture content.)

	Having moved recently to southwestern New Mexico after 37 years in
Minnesota, I can understand why these moisture-sensitive building
techniques work so extremely well down here... and will concede readily
that a FC dome in southern New Mexico, even half below grade, is going to
work many more times than not because the drying regime *far* outstrips the
wetting regime.

	On that note, and dipping back into costs again for a second, it already
seems prudent to consider a FC dome in a moist climate inadvisable unless
heroic moisture-intrusion prevention measures are taken, driving the costs
up significantly. And so if FC is relegated to being the wall component,
with everything else (like the roof, foundation, etc) being typical, this
changes the entire picture. In a typical studwall house, the wall system
represents about 15% of the total materials cost. So if a person got free
paper, free cement, and free sand, and paid for the rest at Home De(s)pot,
they'd save 15% on materials. Yes, 15% saved is 15% saved, but it's already
much more than $7 a square foot... and that assumes free paper, cement and
sand.

	So... How moisture intolerant is it? Has there been a soak test done? How
will it behave in heating climates when the moisture load is from the
interior? What will happen in the spring if snow drifts against it during
the winter? How does it handle freeze/thaw cycles? If the material is
sealed with a moisture barrier (bearing in mind that there's no such thing
as a flawless moisture barrier, paints included), will it "crumble"
internally like adobe does under those conditions? Will it rot and mold,
break down? Like brick, tiny air pockets and channels permeate this stuff
when it's dried, waiting for the opportunity to exhibit unknown and
possibly unforeseen hygroscopic chicanery. At first glance, it appears that
the same cautions required for building with strawbale will need to be
taken with FC, but I have nothing to back that up, and would be pleased to
be wrong.

	On a related note, has anyone besides the Steens tinkered with straw-clay
blocks? Basically they're straw-intensive adobe blocks: same process,
different mix. They've used the things in Mexico in structural capacities,
and found them to exhibit all the qualities that FC has (lightweight,
highly insulative yet with inherent massive qualities, etc... though I
can't imagine that they have the same compressive strength as FC; however,
that kind of compressive strength really isn't needed in most
circumstances, especially in a monolithic structure with no real point
loads like a dome, though it could be handy in non-dome capacities)... and
the things can be made at absolutely *no* cost if a person scythes up their
own straw and digs up their own clay. (The Steens, BTW, have been building
small houses in Obregon, Mexico, which use indigenous and recycled
materials to the extent that some of these places are coming in with
materials costs of *less* than $3 a square foot. Do they look like American
suburbia? Nope. Would an American suburbanite be comfortable in them?
Probably not: too small, no carpet, no air conditioner, no pool.)



   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   Freewheeling autonomous speculation - Think!
      Personality #7 represents only itself.
    M J Epko - duckchow at mail2.greenbuilder.com
               Kingston, New Mexico
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       If you want to waste your time,
       scatter millet and pick it up again.
           - graffiti from Pompeii, 79 A.D.