[Cob] Re: cob rumford fireplace

[Amanda Peck]

I've gathered that the difference between an horno with a chimney and one 
without is that the one without puts soot above the door and the one with 
puts the soot out of sight in the chimney.  If it were indoors, then a 
chimney all the way out the roof would be good.

See Kiko Denzer's book.  Better yet, buy it.

They're not particularly efficient at burning, I've gathered.  Ocean may 
have some other thoughts, since he's familiar with a wood-fired pizza ovens 
in a commercial setting--and Intaba's may be in use long enough in a day to 
have thoroughly fired the clay, if they are the cob horno type.   And the 
whole point of the fire is to get the oven up to 500-600 degrees F.  Then 
you take the coals out.

"My family" in Mexico did one burn a week in their giant outdoor oven, baked 
all day with it, finally putting in a giant (4-6 feet long, around a foot in 
diameter) tamale (called a sacahuil) to cook all night.  It was nicely done 
and still warm the next morning when they took it up to the weekly market to 
sell in portions. A little 18" home oven almost certainly won't hold the 
heat that long.

And lots of people report cracks in their ovens.  They're not that bad to 
repair, if the cracks bothers them.   And the dome shape would mean that if 
it failed enough to collapse it would fall in on itself.

by contrast, the Rumford fireplaces, probably even the outdoor ones, get hot 
enough to keep the soot off the back.  They're intended to warm people, to 
be kept with a good-sized fire in them all evening.  And if they fail enough 
to fall down, that big and as tall as possible chimney on top of the thin 
short to back fireplace is going to go somewhere, most likely forward or 
back.

The Buckley Rumford site mentions that trying to make a Rumford without 
using stone or regular brick instead of fire brick for the inside veneer and 
floor often leads to cracks and spalling, that historic fireplaces show 
signs of damage.  He sells plans, not firebrick (those may come from the 
wood-stove store).  But he does have to promise that fireplaces built with 
his plans will hold up.

But if you're really trying to be all home-grown natural, you MIGHT be able 
to just do the floor and back.  (don't try it with the burn tunnel in a cob 
bench, though)
....................

Susan wrote:

Thanks, Charmaine- I've been thinking about an horno with a chimney/vent for 
cleaner burning (another project.)  Most of the cob oven pictures I've seen 
have only the door opening.

As for the Rumford.....it needs a specific shape and size of throat and 
damper.   Those parts can be ordered from Superior clay, and the specs and 
instructions are on the rumford.com website.  Now, instead of firebrick, can 
the fireplace itself be made of cob?  What's the difference between a cob 
oven and a cob fireplace?

To set your minds at rest, this experiment will be for an outdoor fireplace. 
  I won't be building a residential fireplace for at least two years.
-susan
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