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Re: GSBN:Clay plastered wall passes 1-hour test!

More interesting news and great work! Can't wait to hear more.


on 7.20.2006 4:46 PM, strawnet@...strawnet@...:

> A minor correction...(no this isn't a tit-for-tat thing...) Bill meant to say
> 600 pounds per linear foot rather than 600 psi...
> otherwise an excellent addition to the info I sent earlier.
> As for the water, we decided to go eat lunch instead of tubing...so that
> didn't happen. But Matts and I will be tourists tomorrow and there's no
> telling what sort of trouble we may get into with most of a day to just do as
> we please... and now, I have to decide between a plunge in the pool or what
> Matts is doing now - taking a nap.
> What a life!
> David
> -----Original Message-----
> From: billc_lists@...
> To: GSBN@...
> Sent: Thu, 20 Jul 2006 2:13 PM
> Subject: GSBN:Clay plastered wall passes 1-hour test!
> Hi all,
> Since Bruce is on a plane out of San Antonio and David, Matts, and
> Ben are cooling their heels and various other body parts by going
> tubing down the Guadalupe River, I get to tell you a bit about
> today's fire test.
> Rule #1: Don't move a clay plastered wall once you've built it. When
> we arrived at the lab prior to the tests, we discovered that a 1/8 to
> 1/4 inch crack had opened up on the non-fire side of the clay
> plastered wall. Since the wall had been moved to make room for other
> testing in the lab, we assumed that the cracking probably occured
> during the move. The cracks were patched with some of the same
> material less than 24 hours before the test took place.
> When the wall was rolled up against the oven, several more cracks
> appeared on the unheated side. These were not patched. The heated
> side appeared to be intact.
> Based on what we saw yesterday - specifically, the plaster pretty
> much hanging on by virtue of the stucco wire - we had decided that
> we'd aim for a minimum of a one hour test, and make a final decision
> at about 50 minutes at to whether we thought the wall would survive a
> second hour of furnace time. If it was doing real well and it was a
> pretty sure bet that we'd make two hours, we'd go for it, but if it
> was questionable we'd do the safe thing and stop at one hour and get
> a fire rating for unstaked, unreinforced, clay plastered bales laid
> flat in a load bearing wall. We felt that overall that it would be
> more beneficial to homeowners trying to get insurance to get the one
> hour rating than to take the chance and maybe get no rating.
> The clay plaster performed quite well, in some ways better than the
> cement/lime of yesterday's test.
> Moisture levels in this wall were lower than in the cement/lime wall.
> The highest reading David got was 14%, with the majority being below
> what he could measure (down to 11% or so). None of us were
> particularly surprised as the cement/lime was kept misted for the
> first two weeks and the clay wasn't, and because of the higher vapor
> permeability of clay.
> Because we had put a 600psi load on the wall by means of hydraulic
> jacks pushing up from the bottom, the bottom edge of the assembly was
> exposed to the fire. The wall was built with a piece of ply at the
> bottom edge to act as a 'brick ledge' for the plaster, and that ply
> of course caught fire pretty quickly.
> About ten minutes into the test, a small chunk of the second coat of
> plaster came loose at the bottom of the wall - a triangle about 8-10
> inches on a side. The base coat at that location stood up well for
> the rest of the test.
> Cracking of the plaster (other than that one flake) did not occur
> until later in the test. I'm not sure of the exact time, but it was
> at least a half hour into it, as opposed to twenty minutes into the
> cement/lime plaster. Another thing we noticed was that the clay
> plaster took a longer time to heat up. We were able to observe the
> fire side through several view ports, and the light we were viewing
> with was the glow of the materials inside. The clay took a lot
> longer before it got to the glowing point.
> The first cracks that opened up on the heated side occurred within a
> foot or so of the crack on the exterior. These continued to expand,
> large amounts of flame came from them, and eventually (maybe 45
> minutes into the test) a several square foot section of plaster fell
> away, exposing the straw beneath. The raw bales did not just burst
> into flame as we expected - in fact, we could see several straws just
> hanging away from the bale, apparently not burning, even though they
> were surrounded by fire.
> At that point we still felt we *might* be able to make two hours. At
> about the 55 minute mark, we noticed that the straw just inside the
> crack on the exterior plaster was visibly burning, and we chose to
> end the test. Chances of the back wall standing up to the water
> pressure at any place that had been charred all the way through were
> slim. And even though the burning spot we saw was outside the
> official test area (the wall was 12' high by 14' wide, and the oven
> only 10' square), we figured that was a pretty strong indication that
> the test area of the wall wouldn't make another full hour.
> The hose stream portion of the test was uneventful (as much as you
> can call pounding water on the wall can be considered uneventful).
> As with yesterday's test, the remaining plaster (most of which was
> still intact) and the charred straw was quickly washed away, and the
> uncharred straw just soaked up everything that was thrown at it.
> Upon cutting out some of the area on the exterior where we had
> observed the straw burning, we found one channel right along a joint
> between three bales had been burned through. And that was all. The
> straw on either side of that roughly 3-4" diameter burned cavity was
> unscathed. Again, this should surprise nobody, as we know that the
> joints between the bales are our weak spots. We had been pretty
> compulsive about stuffing the joints with straw, but unlike
> yesterday's wall where we had also stuffed in some cob prior to
> plastering, we let the sprayer do the stuffing of clay here. We also
> feel that if we had patched the crack in the exterior plaster the
> fire would not have gotten as much oxygen and probably never would
> have gotten to the back wall.
> So Rule #2 is to compulsively stuff the cracks.
> Dang... I just looked before posting and see that David got his post
> out before I did. Well, now you have more details, anyway.
> (how was the water, David?)
> --
> Bill Christensen
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