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Re: Re: GSBN:Gypsum plaster on old Nebraska homes?

>First, congratulations again to you and Coralie...we wish you both a healthy
>and vibrant pregnancy and Fall baby.
>Second, I will need to check with Matts on this, but in our research I never
>remember hearing of gypsum plaster being used alone or in any combination on
>the exterior of any Nebraskan historic straw-bale home.


I will add my congratulations along with Judy's and then echo her
comments about gypsum plaster being used on the exterior of any sb houses
in Nebraska or anywhere else that I know of. One of the problems with
gypsum plaster on the exterior is that it remains susceptable to
moisture, unlike cementitious materials like concrete and cement stucco
that harden permanently when they hydrate and cure.

The use of gypsum as a stabilizer in earth, for a process known as cast
earth (like rammed earth only with a soil-gypsum mix wet enough to pour
into forms like concrete) is that if the wall gets saturated the gypsum
softens and then doesn't provide structural stabilization for the soil.
It the wall stays dry, it's strong, if not, well... There's a reason that
people generally don't use gypsum wall board in exterior locations. Look
at what happens to scraps of it left out in the rain.

On the other hand, something most people don't know about gypsum plaster
is that it is used for wall board because of its fire resistive
properties - which are mainly due to the presence in the gypsum of a lot
of chemically-bound water that is released when the gypsum gets hot
enough. This is how gypsum wall board is able to provide fire protection.
When a fire heats the gypsum, the temperature doesn't rise above the
boiling point of water until all the water is driven out of the gypsum.
Since it takes a lot of energy to accomplish that, the temperature on the
unheated side of the wall remains relatively low until all the water is
driven out. Only then does the temperature of the wall board starts to
rise. This enables a thin material like wall board to provide a period of
protection that is more than one would guess would be the case based on
its thickness alone or on its insulating characteristics - which are

So in fire sensitive buildings like public spaces, schools, etc. using
gypsum interior plaster over straw bales will give fire safety and
building code officials more comfort and confidence in the fire-resistive
properties of the wall assembly.

My two cents worth.


David Eisenberg, Director
Development Center for Appropriate Technology
P.O. Box 27513, Tucson, AZ  85726-7513
(520) 624-6628 voice / (520) 798-3701 fax
<a  target="_blank" href="http://www.dcat.net";>http://www.dcat.net</a>

"Truly appropriate technology is technology that ordinary people
can use for their own benefit and the benefit of their community
that doesn't make them dependent on systems over which they have
no control."             John F.C. Turner