Cob: Rumford fireplaces

[ortoneda]

I've been building a Rumford fireplace out of cob during the last three months and here is what I've learned from that:
- The first problem I've encountered is with the drying time. The fireplace is going to be the main feature of a house, a barn made of stone that will one day be a home. So it was about placing a huge fireplace, 120cm. x 120 cm. with a 6m. high chimney, most of it inside the existing building (I mean that only the last meter or so of the chimney was sticking out of the roof). Such a chimney is almost foolproof, it would work under almost any circumstance, to make it even easier, the wall it is leaning on is an inside wall. 
The sun did not shine on the cob, and a batch of cob was always waiting for the next day in the same room, that may have been a mistake increasing the humidity of the room and the drying time of the cob already on the chimney. The point was that I could only work there 2 hours every second day. Two hours was all it took to build a good 15, 20 cm. high of cob and prepare a batch for the next day. It worked fine for me because I was getting paid hansomely and could combine it with some plastering I was doing nearby, if not I could  never have done it. 
- The second serious problem I encountered was tying the fireplace to the wall. It was a stonewall easy to key to but the cob seemed to lean always forward when wet, and so away from the wall. The solution I found was to plaster the wall first, I don't mean the same day or days before, but well in advance. And then I put sticks, up to 50 cms. long sticking out of the wall every half a meter or so, in pairs, I mean one each side. The fireplace was built thick and then I carved out all the angles when dry. Probably somebody would do it simultaneously with oriented-straw cobs, as in benches and all that. I was having enough problems and did it as I am telling you and it has worked out nicely.
The chimney seemed also troublesome, so I put the sticks in the wall and tied some chicken wire to the sticks as I was getting higher. Wattle and daub would have been a good environmental choice, no doubt, but I was being lucky to have a patient client that would wait three months for a chimney, so why spoil it taking much longer time, and (as I was getting paid by the hour)  taking much more money. Again, that's what I did and it worked out. 
So I guess that is it, my costumer is satisfied with his fireplace, unique in Spain, a magazine made a beautiful report on it that has got me some future costumers and I've spent and enjoyed what I got for it. 
Two more things:
I relied on  the book "Wood Heat" for the measures of the Rumford.
- I once read in a book called "The Earthbuilder's Encyclopedia"( I could be wrong on the title) about a modified Rumford that was designed for corners, does anyone know something on that or have acces to that book?, I'm strongly interested.
- I was forgetting something: My suggestion, for the problems of the drying time and the bonding with the wall would be, when possible, to build the chimney at the same time as the house, which was not possible in my case, or build it in adobe, a much better choice for that because one could offer competitive prices and professional deadlines.
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    -   Mateu Ortoneda Colomar
 Area de  informacion de la Asociacion  de Estudios Geobiologicos  GEA     
c/ Infant Paga,  3, 1
Palma de Mallorca
07010 SPAIN
 web-site: www.gea-es.org
 e-mail: ortoneda at wanadoo.es