>Pumice
Defined
Uses
for Pumice
Worldwide
Application
Hybrid
Applications
Affordable Housing
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 Pumice-Crete® is a low density concrete
made from pumice aggregate, portland cement, and water. It is a
mix that succeeds in providing structural strength and insulation
in one material. Typically it is poured on site in wall thickness
of 14" or greater and no additional insulation or structural components
are necessary. Wall surfaces are finished by applying plaster coats
on the interior and exterior which further aid the thermal performance
by trapping air within the honeycomb Pumice-Crete® mix. The walls
are very durable, fireproof, have good noise resistance, and are
very aesthetically pleasing because they can be formed to fit many
architectural appearances and styles. Being lightweight Pumice-Crete®
is relatively easy to install and is cast on site out of not highly
manufactured ingredients making it a very resource efficient material.
Pumice-Crete® buildings are warm and easy to heat in the cold of
winter and stay cool and comfortable in the heat of summer. Pumice
is a lightweight volcanic rock that is found in many parts of the
world where volcanoes are present. It is a sponge like material
formed by expansion of  gases
while molten lava rapidly cooled. It is a porous glass froth that
is found in very shallow deposits in such places as New Mexico,
Arizona, California, Oregon, Washington, and Idaho. Due to its toughness
and durability it has been used as a lightweight aggregate in concrete
for over two thousand years. It is an inert material and therefore
has no reaction with any of the ingredients of concrete and steel.
Its loose weight, in damp condition, is from 950 to 1300 lbs. per
cubic yard, depending on the grading of the material.
Pumice aggregate is mixed with only enough cement and water to produce
a light concrete with a cured strength of 400 PSI. Only enough cement
is used to coat the aggregate and bind it together where it touches.
This is a lean mix and no attempt is made to fill the space between
the stones. This makes for a honeycomb like material with an evenly
coarse surface. For most one and two story applications this is
adequate structurally and self supporting with no need for additional
support members. More cement increases the strength but reduces
the thermal insulating quality whereas less cement increases the
thermal insulating qualities but reduces the structural adequacy
Our basic mix for exterior walls on a single story  structure
uses under 3 sacks of portland cement for every cubic yard of aggregate
with water being the only other ingredient. This material reaches
400 PSI strength quickly and has a thermal insulating value that
I estimate to be R-I.5 or more per inch. It is no where near the
structural strength of typical concrete used today which are usually
2000 PSI and above but those strengths are not necessary in thick
wall situations.
Low Density Concretes are those that have a cured weight of over
20 pounds per cubic foot and under 50 pounds per cubic foot. The
Pumice-Crete® mix most commonly used weighs just under 50 pounds
per cubic foot once cured which puts it at the heavy end of the
low density concrete spectrum. A yard of Pumice-Crete® weighs around
1250 to 1350 pounds. This is an average weight and can be 10% more
or less depending on actual mix design.
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--SCOTT MACHARDY, OWNER
PO Box 539, EL Prado, New Mexico 87529 machardy@newmex.com
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