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GSBN:Re: fire test -- your opinions?
Bruce, King of Sausalito wrote:
ASTM fire test ... the tentative wall types are two-string Texas
wheat bales---one with bales flat, and one with bales on edge---both
with no pins or mesh, and both with two coats of lime-cement plaster.
the people who will need a fire rating for their building (I suspect)
will also need the higher hardness and durability of lime-cement.
Given that we already we already have data for the fire-resistive
performance of Portland cement lime plasters when used to encapsulate
straw bales and that there are already data and standards in existence
which clearly define the cover requirements and what performance can be
expected of such plasters when used in non-SBC scenarios, it seems doubly
redundant to expend scarce research & testing resources to test identical
PC/lime plasters on almost identical substrates (albeit oriented
Granted, one would expect the strings to fail relatively quickly on the
on-edge stacked bales (elapsed time quite likely predictable based on
existing test data) but one would hope that anyone building with on-edge
stacked bales would know that through-the-wall ties would be needed to
make up for the poorer straw/plaster bond anyway so that string failure
due to edge-stacking should not be an issue.
It could be easily argued that the biggest Brown mark against SBC is the
high embodied-energy content of the cement and/or lime that is used in the
"typical" SBH, (ie slab-on grade foundation, PC and/or lime plaster skins
inside and out).
If the only officially-recognised fire test data "out there" is data for
PC/lime plasters then those will likely be the only plaster types that
will be recognised by the officials who decide upon what gets written into
the Codes or gets built in their jurisdictions for a long, long time.
(Remember the rebar pins requirement ?)
In most parts of the world outside of Krazy Kalifohnia (where the
landscape spontaneously self-combusts on a regular basis) fires begin on
the interiors of buildings and it is the fire resistance of interior
materials that are of primary concern.
There is really no reason why we should not be promoting the use of
earthen plasters on interiors since its weakness (poor weathering
resistance) is not an issue on interiors.
There is no doubt in my mind nor should there be in that of any building
or fire official that 40mm or more thickness of a Portland cement or lime
plaster is at least as fire resistive as any of the conventional cladding
materials that are routinely used in urban housing situations -- vinyl,
wood or aluminum siding, synthetic stucco-covered polystyrene foam boards
Nor is there any doubt in my mind that Portland cement/lime plasters do
not provide sufficient protection against rain wetting of SB walls if the
plaster is fully exposed.
If SBC were to gain widespread use in urban scenarios, I doubt very much
that the tight confines of urban and suburban lots would allow for the
widespread use of wrap-around porches and sufficiently wide overhangs that
would be required to provide adequate protection for fully exposed
So that tells me rainscreen claddings will likely be the cladding of
necessity in urban situations and since bales need to be fully
encapsulated by plaster, even beneath rainscreen claddings, do we really
want to be creating a scenario where future SBH builders will be required
to use PC/lime plasters under those rainscreens even though the weather
resistance/hardness/durability aren't really required and where earthen
plasters (albeit slightly thicker to make up for lower strength) would
serve quite nicely ?
I say if only two walls can be tested, test one with PC/lime plaster on
on-edge bales if you absolutely must test a PC/lime plaster, but the other
one absitively & posolutely should be an earthen mix, preferably a mix
that is *the* best in the SB World so that the numbers that do result,
will amaze the pants off of the officials.
=== * ===
Kanata, Ontario, Canada
<ArchiLogic at chaffyahoo dot ca>
(winnow the chaff from my edress in your reply)
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