Cob Re: fibrous cement

[Gordon & Laura Solberg]

>To: M J Epko <duckchow at mail2.greenbuilder.com>
>From: earth at zianet.com (Gordon & Laura Solberg)
>Subject: Re: fibrous cement
>
>MJ/Mark --
>
>        Thanks for your response to my response.  My article on fibrous
cement in Earth Quarterly was essentially quoting Mike McCain and Sean
Sands.  I think that direct responses from each of them would be very
interesting.  I have e-mailed our respective messages to Mike via friends in
Crestone, and will mail them to Sean in Canada.  Whether or not you get a
reply is up to them.  In the meantime, I'll respond to you directly, with
the best of my understanding.  I'll pull some of your statements out of your
message and reply to them:
>>
>
> I was thinking of a finished minimalist home with the niceties
>>we've come to consider essential like plumbing, electricity, possibly a
>>heat plant, etc - not a minimalist rain shelter. I confused the use of the
>>word "house" with my use of the word "home." My misunderstanding.
>
>        It's a matter of definition.  One person's home is another person's
minimalist rain shelter.
>>
>>	
>> In light of the many variables in numbers that exist for so many
>>materials, I'd be interested in knowing how the R value of FC was
>>determined, what the testing conditions were, the mix and density and
>>moisture content of the material tested, etc.
>
>
>        It will be up for Mike to say where the 2.8 figure came from.  I
talked to Eric Patterson in Silver City.  He hasn't had an official R value
test made on his f.c. formulation, but had comparison tests made, comparing
f.c. with other substances, at New Mexico State U.  According to Eric, f.c.
was comparable to fiberglass insulation.  Eric uses R 3.0 when he talks
about f.c.  He said that he was going to roust through his papers and send
me a copy of the test results.
>>
>>	Of course, that doesn't take mass-effect into account. FC is quoted as
>>being "a substance that has a high insulating value and a high thermal
>>mass, all in one package. There is no other building material that can make
>>this claim." Other building materials coming to mind that likely would have
>>a viable shot at the banner would be the lightweight air-entrained
>>fiber-plus-binder products like Faswall, Rastra, etc., and possibly a
>>couple of the manufactured strawboard products.
>
>        This is very likely.  I think any product that has mass/insulation
mixed together would fall into this ballpark.  What's interesting about f.c.
is that here we have individual sand grains separated rather widely within
an insulating matrix, so that it takes a relatively long time for heat to
flow from one sand grain to the next.  This is an intuitively fascinating
idea, but I think that considerable laboratory testing would be required
(using different concentrations of sand) before we could get a clear idea
about the advantages, if any, to the concept of mixing sand into the mix for
this purpose.  
>
>
>
>>
>>	Every wall material has both mass value and insulation value; FC is
>>ostensibly striking a balance between the two. In the same paragraph, the
>>quote continues "... a fibrous cement wall will take all day to warm up,
>>and all day to cool down." That's exactly what adobe and cob proponents
>>have been saying for centuries, and strawbale proponents for a hundred
>>years... hardly a "revolutionary" statement.
>
>        I think it would take experimentation to pin all this down.  Just
think, for the price of one B-1 bomber, we could do all the research
everybody on these lists can possible conceive of, and then some.  I'd like
to compare uninsulated adobe, adobe with foam on the outside, f.c. with
sand, and f.c. without sand (for starters) under different temperature
regimes and see if they really do "take all day to heat up and all night to
cool down." Specifically, to what extent do they heat up and cool down, and
how fast do they do so.  
> 
>>
>>	I run into another quandary there in that statement, and not just with FC:
>>typically, depending on density and other characteristics, diurnal
>>temperature swings affect only the first couple inches of a given mass, as
>>I understand it - even in the case of direct insolation. Perhaps that was
>>the intended meaning: that when it's hot during the day, the wall will heat
>>up to a certain depth from the sun on one side and warmed interior of the
>>structure on the other, to a depth of maybe an inch or so on either side
>>(since FC is so highly thermally-resistant), but not all the way through
>>during the course of a day... then when it's cold at night, it'll radiate
>>that heat back into the room and to the outside. All materials do that to
>>different degrees. The quandary I run into is in my understanding of how
>>mass walls work. I could be wrong; I often am. Correcting me will help
>>everybody, so if I've presented something incorrectly, somebody speak up:
>
>
>        I think that intuition will carry us only so far in this situation.
Has anybody done temperature measurements with thermocouples imbedded at
different depths in the wall, so that the heat transfer dynamics can be
accurately determined?  If so, I ditto the above request:  please speak up.
>
>
>
>>
>>	Over time (how much time depends on the material... we might assume that a
>>12" FC wall of R-33.6 might take as much as several days before it reaches
>>core-temperature stability), the effects of diurnal temperature
>>fluctuations on uninsulated mass walls (which is what a FC wall is when
>>we're talking about it in this capacity... K-Value, the measure of thermal
>>'transmissivity', and its inverse sibling R-Value, the measure of thermal
>>resistivity, are not mutually exclusive: they co-exist, and can't be turned
>>on and off) in generally-cold or generally-hot climates can be disastrous
>>to comfort. If a diurnal thermal flywheel effect is invoked in a place
>>where the mean summer temperature is 90F (which is not determined by
>>averaging the daily high and daily low temperatures, but by charting
>>hour-by-hour or even minute-by-minute temperatures... in other words, a low
>>of 70F at night and a high of 100F during the day is an average of 85F; but
>>if it's 100F for three hours during the day, and 70F for a half-hour at
>>night, they don't cancel each other out), the wall will naturally want to
>>moderate to an uncomfortable 90F or so over a course of days, at which
>>point the wall's ability to absorb a given day's heat (thereby making the
>>house feel cooler) will be all but lost. The house will feel like an oven.
>>By the same token, in a cold climate where the mass wall's core temperature
>>dips to 25F, the heat plant (whether passive solar, woodburning, whatever)
>>will be working to not only heat the interior, but the infinite-heat-sink
>>of mass wall which keeps dumping the warmth outside.
>
>
>        Yes, this is one disadvantage of underground houses in cold
climates.  I think the ideal house would have several different areas:  an
underground "cave room" for daytime summer comfort, a screened sleeping
porch for nighttime summer comfort, a glassy sun room for winter days, and a
highly-insulated room for winter nights.  Thermal mass can become foe rather
than friend under the conditions you outline above.
>
>
>
>>	Strawbale might be the better answer for those climates where the extended
>>average seasonal temperatures are fairly well above or fairly well below
>>the comfort level, since it has about two inches of highly-insulated dense
>>mass on all the interior walls... just enough to accommodate diurnal swings
>>effectively without it turning into a losing battle, and in such an
>>arrangement (extremely well insulated) that the real financial costs (if
>>any) of heating or cooling the mass are minimal.
>
>
>        Please expand on this so that I can get a better idea of what you
are saying here.  Particularly  "two inches of highly-insulated dense mass
on all the interior walls."
>
>
>>
>>	Also on that subject, it should be pointed out that every one of Mike
>>McCain's objections to strawbale construction given on page 14 of Earth
>>Quarterly #1 is answered by one or more lower-cost and easier options...
>>and several of his broad assertions were exactly wrong. I know that they
>>there were his comments, not yours, and that you don't necessarily agree
>>with them. I feel compelled to point out, however, that the only validity
>>his comments have is in the context of a couple of needlessly-restrictive
>>strawbale codes which exist in contrast with proven viable strawbale
>>techniques (such as using them in a loadbearing capacity) and other codes
>>adopted in other municipalities. I find it alarming when somebody
>>authoritatively compares an apple with an orange, when all they've ever
>>done is licked the outside of the orange. Of course it was bitter; he
>>didn't take the time to get to the good stuff. But I guess it's better to
>>have a bitter outside and a sweet core than vice-versa. If you'd like me to
>>answer his extended quote point-by-point, I will, but not to the cob list,
>>where it would be too far off-topic. I'll happily answer it to the
>>strawbale list, or privately. And you can be assured that I won't be
>>speaking in any sort of authoritative manner about FC until I actually have
>>some sort of authority in the subject... which is what I'm pursuing with
>>you here, with all my questions and skepticism. I really do want this stuff
>>to be the cure-all that it might be.
>
>
>        This is for Mike to answer, not me.  I was but the messenger.
Rebuttals are always welcome in EQ if you are interested.
>
>  
>>
>>	I'm still not sure what to make of the moisture question. On one hand,
>>there's somebody soaking down his floors for 2-1/2 years to grow snails...
>>on the other hand, "[f]ibrous cement absorbs water, so precautions must be
>>taken to prevent this, especially in wet climates." 
>
>
>        People generally prefer a drier environment than snails.  In the
context of the article, "precautions" refers to human comfort, not
structural problems. However, I have talked to Eric Patterson since then,
and he is of the opinion that f.c. will begin to break down if it remains
moist for too long.  How long? For the price of one B-1 bomber ashtray, we
could do the research and find out.
>
>
>
>It soaks up water "like
>>a sponge" and doesn't deform under saturation conditions, yet you can press
>>on it when it's soaked and water seeps out (which indicates deformation
>>from simple hand pressure). Perhaps I'm looking for answers where none
>>exist. I do that fairly frequently.
>
>
>        I think the more precise phraseology would be, "doesn't deform
significantly under saturation conditions."  I would love to see compressive
and tensile strength + deformation tests done with f.c. when it is bone dry,
after it has picked up all the moisture it can from a 100% humidity
environment, at full saturation, and at different levels of saturation in
between.  Paying for this would mean robbing the bomb release control lever
off that B-1 bomber.   My guess is that tensile strength would degrade
rapidly with increasing moisture content, and compressive strength would
degrade much more slowly.   
>
>>
>>	I'll look forward to any information, observations, thoughts and ideas
>>that you'd care to impart; my ears and mind are open and waiting.
>
>        Thanks; I'm sure that I'll have a lot more to say about this after
I have my little f.c. office built and can see how it performs in real life.
>
>
>                                                Gordon Solberg
>                                                www.zianet.com/earth
>
>p.s.  I will post this on essa and cob; feel free to post it on straw if
you want.  
>