Hi Duane,
Your results are close to inline with my experiments, but I don't
agree with your conclusions. Papercrete can be made such that it
will not continue to smolder. Please continue to experiment.
I've conducted ALMOST the exact same test you conducted. I didn't
use any borax in a 1:1:1 paper, portland, sand test mix and obtained
very similar results.
2-1 ratio of portand to paper seems to be very close to the point
where papercrete begins to become non smolder supporting.
All papercrete will char on the surface when exposed to a torch in
the manner you conducted your test. Higher mineral content mixes
will not continue to smolder. Also keep in mind that air circulation
affects the test. If the small embers are fanned sufficiently they
will tend to smolder hotter and longer.
I'm curious about your logic about using a mixture of both boric acid
and borax. One is acidic the other is alkaline. It seems they would
chemically react and form a boric salt and a little (very little)
extra water. I don't know if boric salt has the same combustion
retarding properties as plain borax. I also don't know if boric salt
will penetrate inside the paper fibers the same. 8% borates seems
very high and should have produced much better results than observed
in your test. I'm wondering if the acid/alkaline reaction might be
the reason. Just guessing.
Keep in mind that portland is not the only material that can raise
the mineral content to bring papercrete's fire resistance up to a
level that it will not continue to smolder. Clay works very well.
1:1:1:1 paper, portland, clay, sand with some plain borax will fare
far far better. It might continue to smolder for a short time, but
it will not consume the whole sample as you experienced.
Alternatively 2:1:1 portland, paper, sand with plain borax will also
fare well.
2:1:3:2 paper, portland, clay, sand with some plain borax will also
fare well, but will take longer to dry.
I encourage you to keep experimenting and reporting your results.
The experiment you conducted is not a failure. It's part of the
learning process.
One more thought. When did you add your borates? My rule of thumb
is to add the borax to the paper as soon as possible during the
pulping process. This gives maximum opportunity for it to soak into
the paper.
(All ratios I listed are BY WEIGHT)
Keep having fun. Keep sharing.
--- In papercreters@yahoogroups.com, "mdumiller" <mdmiller1@...>
wrote:
>
> I ran a fairly unscientific but interesting fire-resistance test on
a
> PC sample I had made. From what I see, I'm not convinced that PC
can
> be made totally fire resistant without a lot of additives
(increasing
> its cost to make). My mix included a borax/boric acid mix in a
> weight ratio equal to what the forest service recommends for making
> wood more fire-resistant.
> What was interesting was that the material never at any time as a
> fuel source produced an open flame, only smoldering. Another fact
I
> found interesting was that the block continued to smolder for
twenty
> minutes after the propane torch was removed, looking like a piece
of
> charcoal from the barbecue grill. I would imagine that doubling
the
> portland would slow the smoldering, but I had hoped the borax/boric
> acid mix would extinguish the block once the torch was removed--but
> no luck.
> Some type of integral firestopping might makes sense when PC is
used
> in a wall to limit the spread of the smoldering, since ultimately
the
> block was consummed. To play it safe, I believe that the wall
> surface should be coated with a plaster or gypsum product to
prevent
> the smoldering from starting. Here is a link to pictures:
> http://www.domovitae.com/fcrete/pcfire.htm
>
> food for thought - Duane.
>
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