As Nick pointed out. I'm referring to a papercrete wall, not a
strawbale wall. I only mentioned strawbale to compare and contrast
some of the issues.
The problem with using a simple humidity sensor is that humidity
sensors measure moisture in the air, not in the bulk material a wall
is made of. Keep in mind that it is my intent to allow my walls to
be vapor permeable to the outside. Therefore the humidity of any air
inside the wall will change dramatically faster than the actual
moisture content of the wall itself.
To illustrate, imagine a nice dry sunny day an hour after someone
turned off their lawn sprinklers. While the humidity level close to
the ground gives a little hint to what is happening inside the
ground, simply walking across the ground to see if your footsteps are
squishy is probably a better measurement. :)
When something gets wet, it tends to dry from the outside surfaces
inward. Measuring the weight of the bulk material when it is known
precisely what it should weigh when perfectly dry will give a very
accurate measurement.
*(Temporarily changing the subject to strawbale for comparison)
I also point out that it would be more difficult to have this 'core
samples' system for a strawbale wall. Straw Bales simply don't core
as easily. It's not impossible, of course, just more difficult.
*(Back to discussing Papercrete now)
As far as measuring .01 grams, I don't need that level of accuracy.
If I make each sample large enough, say .1 kilo (dry) or more, then
tenth of a gram accuracy on the typical postal scales will produce
one tenth of a percent resolution in mass measurement. I'm
comfortable with that. A typical papercrete might have a dry density
of about 160 kilos per cubic meter (It varies widely depending upon
the recipe). A tenth kilo core sample in that example case assuming
a very typical 30 centimeter thick wall, would be a little less than
8 centimeters in diameter. An 8cm hole in a wall very workable
without compromising any structural issues in the wall.
If I have a large number of samples, I will be able to learn a great
deal.
--- In papercreters@yahoogroups.com, sire@... wrote:
>
> I suppose you have thought this through, and not to rain on your
parade as it were, but do postage scales measure hundreths of
grams? Is the density of water vapor in your papercrete plugs the
same as its density in the straw? Do you have a way of converting 1
gram of additional weight in your plugs to relative humidity?
Because at some point you will have to talk to the rest of the world
to communicate your findings.
>
> Wouldn't it be simpler and easier, assuming you want to use holes
in the straw, to periodically insert humidity sensors?
>
> Neal
>
> -------------- Original message --------------
> From: "slurryguy" <slurryguy@...>
> Papercrete may have an advantage over strawbale when it comes to
monitoring moisture levels. Strawbale has struggled for years to come
up with moisture sensors that are effective, accurate, and durable.
>
> My plan is to not try to get fancy at all. I plan to drill a series
> of holes into my walls and then fill the holes with a perfectly
sized papercrete plug going all the way into the wall. The plugs will
all be carefully sized to exactly fit the hole and all the plugs will
weigh exactly the same amount. I will cover each plug with an access
panel. It will be a simple matter to remove the panel, pop out the
plug and weigh it on an accurate postage scales. Any changes in
sample weight over time will be due to moisture content.
>
> The concept may not be high tech, but it will be extremely reliable
over the long haul, and be extremely accurate. The technique also
lends itself well to visual inspections for other potential issues,
like insects or mold and such things. It also is extremely
inexpensive.
>
> It will be important to seal the inside and outside surface well,
so that core sample gets it's moisture from the surrounding wall, not
by leakage from the hole to the outside.
>
> --- In papercreters@yahoogroups.com, "ElfNori" <elf@> wrote:
> >
> > Also, it might be worth embedding moisture sensors in each walls
at the bottom inside the waterproof layer and directly above that
sensor in the regular papercrete part of the wall. I don't want to
spend a lot of money on this, but I think the sensors would tell us a
lot.
> >
> > Dusty? Yes? No? Thoughts?
> >
> > ElfN
> >
>
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