[Strawbale] [SB-r-us] Strawbale passes fire tests!

[billc]

At 5:46 PM -0700 7/20/06, Nancy or David Gray wrote:
>Hello. Grand kudos to you folks and what a great group. You must 
>have had a lot of fun.

Yeah, it was a great group.

>Thank you for going the load-bearing route and the on-edge method. 
>Many in the past stressed on-edge would be bad in a burn. Guess they 
>might, but then anything is bad in burn unless it's covered with 
>cement-lime plaster it seems.

Actually, according to the lab guys, "everything burns eventually". 
They should know, they do it all the time.

In some ways the clay plaster did better than the cement/lime.  It 
took longer to get to the point where it glowed, and aside from one 
smallish triangle of second-coat plaster coming off early, it didn't 
start cracking 'til ten minutes later than the cement/lime.

We're pretty confident that if we were to do the same test again we 
could do a better job on the clay plastered wall and get it to two 
hours as well.  Some factors that played against us were that there 
was not as much clay on the "cool side", and not enough straw mixed 
into that clay, so when they moved it up against the furnace the cool 
side cracked, letting air in.  This allowed the fire to get back 
through a gap between three bales (well stuffed with straw, but still 
an obviously weaker point) and burn all the way to the cool side.  In 
retrospect, we should have patched that crack.

By the end of the cement/lime test, the only thing holding the 
plaster in place was the stucco mesh.  I suspect that the clay 
plaster probably would have completely delaminated by the end of two 
hours as well - in the area where a large chunk fell off, the bales 
took the full brunt of the 1600+ degrees (F) for a good twenty 
minutes, and the charring only got to the depth of the first wire on 
two wire bales (18" wide) except in the gaps between bales and 
courses.  Maybe three inches deeper in those joints.  So there was a 
good 9 or 10 inches of  bale left, easy, everywhere except for where 
it was cracked on the cool side.

Between the slower heat absorption of the clay and the additional 4" 
of straw with the flat instead of edge bales, the temperature rise on 
the cool side was extremely low.  I wasn't watching the temperatures 
as closely on the clay plastered test, but the one time I did look - 
maybe halfway through the test - the temperatures on the cool side 
were just a few degrees above ambient.    I know they jumped up after 
a large chunk of heated-side plaster came off, but I don't know how 
high.  They were certainly well within the allowed average of 275 
degrees above starting temperature.
-- 
Bill Christensen
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