Cob: Masonry heaters

[Shannon C. Dealy]

On Sat, 12 Jan 2002, Banks wrote:

> I'd like more info on cob heaters, too, but with metal 'innards' like a
> draft-controlled firebox to direct heat to a cooktop & oven.  Could this be
> done?

Yes, though a simpler approach might be to simply use the top of the
"chimney" drum in a bench stove design.  The top of this drum is
the hottest exposed surface of the bench stove and could be used to cook
on.  You might also try putting a small oven rack on top of the barrel
with some kind of a large cover in order to make an oven out of it (I
don't know if anyone has ever tried this, spur of the moment idea :-)

[snip]
> I wonder how the cob would hold up.  Would the iron change sizes with
> heating/cooling, crumbling the cob.
[snip]

Cob bench heating systems often embed a large steel drum into the bench,
from what I have seen, generally crumbling of the cob where the drum is
surrounded by a very thick layer of cob is limited to a very thin layer
immediately around the drum and does not propagate to the rest of the
bench around it.  Where people have tried to do something artistic or play
with the design so that thinner layers of additional cob are wrapped
around upper portions of the barrel, I have seen serious cracking/flaking
of the cob.

NOTE: every bench stove that I know of was fired immediately after the
bench was built, so the immediate expansion of the barrel while the cob
was still wet (forcing it outward to make room for the expanded barrel),
coupled with the immediate drying of the cob around the barrel due to the
heat, very likely plays an important part in keeping the cob from cracking
over time.

Shannon C. Dealy      |               DeaTech Research Inc.
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