About to start mortaring, any comments before I do?

About to start mortaring the brick bell and chimney into place. Back brick rectangle bell will rise to about 1.2m (a bit small methinks, but I have limited space and can't block up the window too much) and the chimney bricks will rise to meet the flue:



I think the dimensions of the fire chamber and riser are right - not properly arranged in the picture.

I reckon the manifold into brick bell and the port into brick chimney are good. The flue is huge and has a constantly powerful pull to it.

I am going to use this clay and sand, after sifting it and getting something of the nice texture I got when testing it between the bricks, as pictured:








I have this stuff, refractory cement, one for the brick laying of the fire brick burn chamber, and another for patching cracks and holes (the A60 stuff):






Planning to throw a cupful of each into a bucket of each clay/sand mortar mix.

Any thoughts about whether I'm on the right or wrong track would be much welcome.

I do plan to cob over the entire thing when it is complete.  

I went ahead with the build. Used it 5 times now for between 2 and 4 hours - works excellently. Cob cracking a bit. Clay/sand plaster holding up 100%. The thing will be plastered at some point with a more elastic cob plaster; gonna use it as is for the coming winter first.

Good work! Sorry I didn't see this when you first posted. I have a few questions... How hot does the chimney face of the brickwork get? Is it similar temperature from bottom to top? Is it similar to exposed faces of the bell? What are the internal dimensions of the feed tube, the heat riser, and the existing flue?

If you are not currently getting good heat from the chimney brickwork, I would suggest opening the top of the bell/chimney, removing as much as practical of the dividing wall, and turning the bell/chimney into one volume. Then run a piece of stovepipe down from the original flue to around 6" above the floor of the bell space (called a "plunger tube"), so only the coolest gases escape from the bell space. This would allow the brickwork nearest the occupied space to be a main part of the radiating mass.

Your pictures are not saved in a way that our software can handle well, for unknown reasons, so I am reposting this one to make it available as a thumbnail for the thread.

Hi Glenn. Thank you for your reply and interest. I am extremely happy with the unit as it is, and, considering the planning and work that went into getting to this point, I am unlikely to make changes.

I tried to answer your questions but realised I'm not sure that I understand them! So let me try describe the heating process rather, based on the longest of 5 or 6 burns so far, which was 4 hours.

The tank/barrel gets very hot very quickly and radiates heat excellently. The brickwork near it gets hot quickly as well, presumably from heat radiating from the tank/barrel. The flue also gets quite hot after an hour. After 2 hours, the cob around the wood feed is very hot, and the heat is starting to be felt coming through the double brick wall below the barrel/tank. Next is the top of the brick bell, which is warm to the touch at 3 hours. At 4 hours, when I let the fire go out, the heat was moving into the chimney-side bricks as well.

Glenn Herbert wrote:What are the internal dimensions of the feed tube, the heat riser, and the existing flue?

Feed tube: slightly off square - 15, 15, 15.3, and 16 cms. So a 230 to 240 cm2 CSA. Basically a 6 inch feed.

Heat riser: 17*18 cms. So a 300 cm2 CSA. (Oh, and I wrapped the riser in foil - I don't have a picture of this).

Existing flue: I think the CSA is 435 cm2. An octagonal flue with each side 9.5cms.

So a huge flue for the unit, with the result being a powerful pull. Possibly too powerful, which is a good problem in my opinion. I climbed onto the roof to test the heat coming out the top of the chimney at an average burn rate, and it was just warm on the palm of my hand, so I'm satisfied that the heat is being efficiently pumped out through the barrel/tank, and also stored in the bricks, with minimal heat escape through the chimney.  Not being a perfectionist, I am very happy with the unit!