We were given an old insert style stove (i.e one that is meant to be installed into a wall) and as we have a huge (terrible...) open fire place we installed the stove with gusto.
It doesn't work particularly well and we would like to try and insulate the stove and build a bit of thermic mass using cob and stone. This would involve filling in some of the space between the stove and the fireplace. We would be building two walls on either side of the stove each approx 50cm wide, 1m deep and 1m high , a wall behind the stove, perhaps 2m wide, 30cm deep and 1m high and perhaps 20 or 30 cm thickness over the top of the stove itself. The stove has a large glass fronted door with an ashtray and air intake below. On either side of the ashtray are two grilles designed (I think) to draw air under the stove and up the back. We will probably leave two open channels in the wall behind the stove to allow this airflow to continue.
So, thanks for reading! My main question is, given that the cob and stone will be supported on all sides, do we need to build it layer by layer waiting for it to dry or can we do it all in one hit? Also, could we then run a fire to dry it or would it be better to let it dry (eternally..??) naturally? Its not super hot here! Of course if anyone can see any improvements or errors in this idea please point them out, your eyes and minds are much appreciated
Your concept sound reasonable, I do warn folk that "fire units" of any type have the potential of being very dangerous for obvious reasons. It is hard to recommend something that modifies a system. I also meet many "professionals" that are afraid to give advice for such "changes" so getting them involved can be fruitless as well. I would have them check and clean your chimney, and just see what they in general would say about your system. You can always check back in here.
Now from what you described, I would just pack in the stone and clay till you are done filling in all voids around the stove, leaving the exposed front with a hand fitted stone in the dry laid look, no visible mortar joint. The cob is going to crack considerably and possibly smock if you have fiber in it. Some folk will leave the fiber out, while others will use "furnace gasketing rope" as their fiber material. You may also consider using real lime mortar for the front exposed areas and/or cob/lime mortar mix. Remember, this is still a fireplace and is not going to be very efficient at all. You would be better served with a real wood stove that is fitted into the fireplace opening and perhaps augmented with cobb and stone. Another option is rocket stove that uses the fireplace flue but that is more design than I could describe here safely.
posted 7 years ago
Hi, thanks very much for the feedback. In fact this is a temporary solution until I can build a rocket stove next year. We don't mind if its not perfect because it will be removed anyway, we're more interested that it should help the stove burn at a higher temperature, using less wood and stocking heat better..
I am presently surrounding our wood stove with cob and have found a few lovely examples of it online. I am also following the technique of building cob bread ovens. The layer closest to the heat shouldn't contain organic matter. But then an insulative layer comes after that with plenty of straw. It seems like if done correctly, major cracking shouldn't be a problem. I was worried about doing this so close to the heating season. I would have preferred it to have had a chance to thoroughly dry before lighting a fire. That likely won't be the case. But they seem to start fires in the cob pizza ovens right away and don't have a lot of problems. I hope that will the case for me. If not, I plan to fill the cracks over time.
Great, thanks for the support! I'm gonna have a crack at it asap
posted 6 years ago
Did you ever finish your project? I got the cob in around the woodstove and it is working great. There was minimal cracking. I have learned that it is better to fire the woodstove while the cob is still damp so my fears were undfounded. I still need to cob above the stove around the chimney (want to wrap it with copper tubing for water heating first). But that will wait until the weather begins to warm. Anyway, I am very pleased with my project and the difference it made for our comfort levels (definitely moderated the temperature swing). Hope it worked out for you too.
Collection of 14 Permaculture/Homesteading Cheat-Sheets, Worksheets, and Guides