A Stove I built

[Cal Schindel <calsch@montana.com>]

About twenty years ago I built a stove which fits some of the material
mentioned on this list. I had an old Marks engineering book which I
referred to for temperature ratings of material so I knew as Harry
Parker said that Portland cement was the weak item.

I used sand, a small amount of bubble soap as a surfactant and bubble
entrapment, pearlite beads, and rock wool insulation which I pulled
apart into small tufts by hand, and portland cement. I did not measure
anything and just relied on my extensive experience with concrete to 
get a "feel" for the mix.

I used a 30 gallon drum inside a 55 gal drum. The 30 gal drum is also
shorter which allowed room for a flattened 6 inch chimney pipe sleeve
in the bottom of the 55 gal drum which served as a secondary burning
chamber. I had a secondary air source which was a schedule 40 2" black
pipe feeding over the top of the fire box and down at the back to right
in front of the secondary burning hole which was at the bottom of the
fire box. The smoke would rise into a second 55 gal drum which was
unlined and mounted above the main stove and served as a heat exchange.
In operation, I was able to shut primary air down to near zero opening
and secondary air adjustable as needed. Several times I removed the
adjustment cap to the 2 inch secondary air pipe and looked in to see
it glowing red which means that the air to the rear of the fire box 
was really hot. It displayed a significant draw with a fairly rapid
flow of air with the cap removed.

I also had a guillotine slide and another shortcut chimney into the
heat exchange at the front of the stove. This helps with smoke removal
when opening the door to feed wood and did work fairly well.

After two years use, the inner barrel was warping significantly and
at the end of the third year this warpage was preventing good operation
of the unit and I felt becoming somewhat of a safety hazard so I
discarded the entire unit.

My conclusions were that the overall design was decent and the smoke
was minimal and quite clean but that the inner lining needs to be
entirely of ceramic, fire clay or some such material. The portland
cement mix was very friable and if directly exposed to wood loading
would have broken out in chunks. With a claw hammer I could dig out
pieces of the lining with ease. But the first line of failure was the
inner drum warping.

For what it is worth, Cal

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