It's time to talk about papercrete's counter-intuitiveness again.
I've tested relative R-Value with a homemade calorimeter.
I described the apparatus and testing method in this previous post:
http://groups.yahoo.com/group/papercreters/message/45
My results indicated that compressing the slurry into the form
INCREASED the insulating properties. The more a sample was
compressed, the higher the R-Value. My most compressed sample was
compressed by driving a front tire of pickup truck wheel on top of
the form. I estimate it was greater than 400 PSI compression.
While I think it may be possible to compress wet uncured papercrete
so much that it will start to lose R-Value, I don't think it is
PRACTIAL to overcompress it in a DIY environment. My wild
undocumented guess is that one would need to compress the wet slurry
to thousands of PSI to crush the paper fibers enough to start
decreasing insulation properties.
My sample size in these tests is small and I certainly haven't tested
every possible combination. It takes time and attention to detail to
run a calorimeter test and get good data. Calorimeters are fiddly to
use in the best circumstances.
My theory to explain this phenomenon is that the best insulation is
achieved by trapping air INSIDE the paper fibers. Loosly hindering
air flow BETWEEN fibers is only moderately effective. I think
compressing the slurry tends to push the fibers closer together which
significantly reduces the permeability of the final product to air
infiltration. I also theorize that micro convection currents are
greatly diminished by the denser fibers.
Keep in mind that almost all papercrete with significant paper
content will have higher insulation value than fiberglass batts.
Also remember that cellulose insulation manufacturers list "packed"
cellulose insulation to have a higher R-Value than "loose"
cellulose.
Another point to remember is that the higher the mineral content of
papercrete the lower the insulating value will be. A balance between
strength, weight, and insulation is appropriate. Different recipes
of papercrete for different applications make sense.
The idea that compressing insulation hinders performance applies
primarily to fiberglass batts. Fiberglass fibers are solid glass
rods. Compressing the batts pushes out all the air. Compressing
cellulose only pushes out the loose air. The trapped air inside the
paper fibers remains.
I estimate that a mix ratio of 1:2:1 paper, portand, sand, can reach
R4 with very tight slurry compression. I haven't run any calibrated
tests to determine if this is correct. I'm very confident that a mix
ratio of 1:1:1, paper, portland, sand will go well above R4 with
slurry compression. Perhaps as high as R5. Again, I haven't done
any calibrated tests to prove it.
--- In papercreters@yahoogroups.com, "mdumiller" <mdmiller1@...>
wrote:
>
> I haven't tested this theory, but I think the amount of water
> reabsorption of cured papercrete is related to the amount of
original
> water in the mix as poured/used. As the water evaporates from
curing
> PC, creating airspace voids in the pC, rewetting will tend to
permit
> water back into these itsy spaces. The fibers are probably encased
> in portland and don't absorb much, which is why a block that is
> rewetted dries so quickly.
>
> I'm guessing that if you took two identical just-poured pc blocks
and
> squeezed all the water out of one of them and let them both dry,
the
> one with the water squeezed out is smaller and of higher density
and
> probably won't absorb as much water. It contains less air space,
> even though they both contain the same amount of paper and other
> material.
>
> On the other hand, if you don't put in enough portland to coat the
> fiber, then the paper fibers themselves will saturate and become
part
> of the equation, and in this case, I think you're right.
>
> In situations where you expect to have PC exposed to a lot of
> moisture, based on this theory, it would be wise to compress the
> blocks while wet to eliminate water. Obviously this could impact
the
> insulative properties of the finished product. And this is just a
> theory, so don't do anything based on this untested crazy idea.
>
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