[Cob] fly ash in cob or plaster (was fly ash in foundation)

[Barbara Roemer]

This section from wiki entry on fly ash may be pertinent.  If it does tend
to pop out, wouldn't make a good additive for plaster, though could still be
used in cob....

Also, see another section from the same query on fly ash, but scan down for
heavy metal info which I've pasted in below the bricks entry.  Seems that
binding up the fly ash in concrete or perhaps cob would be a better use than
that as a plaster in an inhabited structure.

Barbara

Bricks

Ash bricks have been used in house construction in Windhoek,
Namibia<http://en.wikipedia.org/wiki/Windhoek>since the 1970's. There
is, however, a problem with the bricks in that they
tend to fail or produce unsightly pop-outs. This happens when the bricks
come into contact with moisture and a chemical reaction occurs causing the
bricks to expand.

In May 2007, Henry
Liu<http://en.wikipedia.org/wiki/Henry_Liu_%28civil_engineer%29>,
a retired 70-year old American civil
engineer<http://en.wikipedia.org/wiki/Civil_engineer>,
announced that he had invented a new, environmentally sound building
brick<http://en.wikipedia.org/wiki/Brick>composed of fly ash and
water. Compressed at 4,000
psi <http://en.wikipedia.org/wiki/Pounds_per_square_inch> and cured for 24
hours in a 150 °F (66 °C) steam bath , then toughened with an air
entrainment <http://en.wikipedia.org/wiki/Air_entrainment> agent, the bricks
last for more than 100 freeze-thaw cycles. Owing to the high concentration
of calcium oxide <http://en.wikipedia.org/wiki/Calcium_oxide> in class C fly
ash, the brick can be described as "self-cementing". The manufacturing
method is said to save energy, reduce
mercury<http://en.wikipedia.org/wiki/Mercury_%28element%29>pollution,
and costs 20% less than traditional clay brick manufacturing. Liu
intends to license his technology to manufacturers in
2008.[12]<http://en.wikipedia.org/wiki/Fly_ash#cite_note-11>
[13 <http://en.wikipedia.org/wiki/Fly_ash#cite_note-12>

Environmental Problems

Fly ash, like soil, contains trace concentrations of many heavy
metals<http://en.wikipedia.org/wiki/Heavy_metals>that are known to be
detrimental to health in sufficient quantities. These
include nickel <http://en.wikipedia.org/wiki/Nickel>,
vanadium<http://en.wikipedia.org/wiki/Vanadium>,
arsenic <http://en.wikipedia.org/wiki/Arsenic>,
beryllium<http://en.wikipedia.org/wiki/Beryllium>,
cadmium <http://en.wikipedia.org/wiki/Cadmium>,
barium<http://en.wikipedia.org/wiki/Barium>,
chromium <http://en.wikipedia.org/wiki/Chromium>,
copper<http://en.wikipedia.org/wiki/Copper>,
molybdenum <http://en.wikipedia.org/wiki/Molybdenum>,
zinc<http://en.wikipedia.org/wiki/Zinc>,
lead <http://en.wikipedia.org/wiki/Lead>,
selenium<http://en.wikipedia.org/wiki/Selenium>,
uranium <http://en.wikipedia.org/wiki/Uranium>,
thorium<http://en.wikipedia.org/wiki/Thorium>,
and radium <http://en.wikipedia.org/wiki/Radium>. Though these elements are
found in extremely low concentrations in fly ash, their mere presence has
prompted some to sound alarm.

The U.S. EPA <http://en.wikipedia.org/wiki/EPA> has said in the past that
coal fly ash does not need to be regulated as a hazardous
waste.[15]<http://en.wikipedia.org/wiki/Fly_ash#cite_note-14>However,
a revised risk assessment may change the way CCW is regulated
[16] <http://en.wikipedia.org/wiki/Fly_ash#cite_note-15> Studies by the U.S.
Geological Survey <http://en.wikipedia.org/wiki/USGS> and others conclude
that fly ash compares with common soils or rocks and should not be the
source of alarm.[17] <http://en.wikipedia.org/wiki/Fly_ash#cite_note-16>

[edit<http://en.wikipedia.org/w/index.php?title=Fly_ash&action=edit&section=16>
] Contamination in Byker

In the 1980s and 1990s, around 2,000 tons of fly ash from local incinerators
were used by the local council deliberately to surface footpaths around the
Byker <http://en.wikipedia.org/wiki/Byker> and
Walker<http://en.wikipedia.org/wiki/Walker,_Newcastle_upon_Tyne>districts
of Newcastle
upon Tyne <http://en.wikipedia.org/wiki/Newcastle_upon_Tyne>,
England.[18]<http://en.wikipedia.org/wiki/Fly_ash#cite_note-CAT-17>Considerable
concern was raised in the local community when this was
discovered. Later studies found contamination by dioxins and furans from
this fly ash, although no strong evidence for heavy metals (the area has an
industrial past that may explain the leves that were
found).[19]<http://en.wikipedia.org/wiki/Fly_ash#cite_note-U._NCL.2C_Byker-18>