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GBlist: GBlist slip form walls



There was some recent discussion on the use of foam as the insul. for a
masonry sandwich. There was also some discussion about a month or so ago
where I mentioned that we have used EPS foam for both slip form rock
walls and concrete walls. 

EPS foam (used by itself) is quite inexpensive. It is expanded with
pentane which dissipates very rapidly from the time of manuf. - at the
point of installation it generally can be considered inert. The plastic
itself (a benzene polymer) is considered stable within normal
temperature ranges. I have never been entirely comfortable with using
plastic especially chlorinated plastics but given the need to insulate
and provide some barrier for moisture transmission and do this at a
reasonable cost - this product works. My only concern is with proper
application as water diffusing through the conc. can run on the surface
and collect in openings or breaks in the masonry.

One alternatives that I have not worked with but given time would like
to incorporate are: Mineralwool in higher densities. Roxul, Fibrex and
probably other companies manufacture high density mineral wool boards in
varying thickness (up to 6"?). Some are manuf. as a insulating
drainboard, others as a high thermal resist. for industrial
applications. Rvalues are approx. 4/inch and the material would be free
draining which could be an advantage. Urea formaldehyde is used as a
binder (approx.2% content) the fibres are larger and coarser than the
equiv. glass products which should reduce risk in exposure.

Use of a mineral wool board would not provide any moisture barrier but
I'm not sure that this is a problem and might be an asset as the wall
material itself (depending on cement content and curing) has a degree of
moisture resistance, is not a material that will  suffer from periodic
high contents of moisture (care in detailing as moisture can be
transferred to other materials). Air and moisture filtration and
diffusion characteristics of the wall are calculable and might
(should/could) be used to some benefit.

Perhaps the most interesting (for my sensibility) alternative to
investigate for slip form walls is the insulating potential of the
concrete binding mix itself. As long as sufficient strength or stiffness
remains to bind the rock material a large number of materials that have
the potential to create air pockets or contain air (chopped straw, etc.)
can be used. Enough research on mixes of this sort have been done to
adequately predict insulation values to be able to make a reasonable
performance design that would be acceptable for most code requirements.
The wall would be thick and would have to probably incorporate some
steel (or bamboo) for additional reinf. stiffness. but it would be
lighter, would have a reduced cement content, would be free of plastics
and would have an appealing simplicity of design in the materials used.

John Salmen
TERRAIN E.D.S.
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