How much crack is too much crack?

[Marcel]

#58

(M) Tarik, you wrote in part:

(T) "We also went with an 8.5 inch x 13 inch chimney peice as the first part of the chimney/vent area. Do we need to narrow it down as we go up, or will this be fine. It appears that this short peice also draws really well already."

(M) I'm making my own chimney cap and it will narrow only for the last 5" of 17". My understanding is that the smaller aperature will produce a Venturi effect, speeding the exhaust and thereby increasing the draw of fresh air into the oven. But if yours draws well now, I would be leery of decreasing that opening too much. Mine will only narrow about an inch in both directions at the top. But I may be making a mistake as I only have an 8" x 8" clay liner, and those are the outside dimensions. If you start to narrow yours with the next chimney piece you'd first of all have a hard time making a smooth interior taper, and then, if you make your chimney of 4 pieces of 1 foot each, you may end up too small at the top. "If it ain't broke, don't fix it" is probably advice which I also need to follow.

(M) If you want to see my latest images, go to the Photo Forum in about an hour.

Ciao,

Marcel

[aikitarik]

In the end, I decided to go up 4 segments of 8.5x13 inch flue segments, mortared together with steed studs to act as bracing for the inevitable earthquake. We still have picked out a chimney cap to keep out the weather, but we'll work that out.

[james]

Tarik,

I did one with a terra cotta tile that worked like a little roof. I set bricks on either side, to let the smoke out either side. I stucco'd the brick to match the concrete chimney pieces. It looked pretty good. It's the San Gimignano oven here:

http://fornobravo.com/pizza_oven_pho...gimignano.html

James

[aikitarik]

Originally Posted by james

Tarik,

I did one with a terra cotta tile that worked like a little roof. I set bricks on either side, to let the smoke out either side. I stucco'd the brick to match the concrete chimney pieces. It looked pretty good. It's the San Gimignano oven here:

http://fornobravo.com/pizza_oven_pho...gimignano.html

James

Ooh... very nice...

We're gonna do the dragon/gargoyle thing that you did, except we'll probably go so far as to arrange for smoke to come out the mouth. My wife is pretty insistant on that point.

But to cap the chimney... I'm still toying with ideas.. I do like this one as it could tie into the red roof (tile or metal) we want to install.

[Marcel]

#78

(M) Tarik, did you mortar the re-bar to the inside, or outside of your clay liners? __________

(M) I have a thought for a temporary chimney roof. Consider cutting the 5th liner (if you have an extra) on the diagonal with your angle grinder masonry blade. That should produce 2 ninety degree tile roofs that you may be able to balance over the opening until you decide on something more decorative. If you leave some of the adjacent corner edges you'd have one roof too small but the larger one would look more finished. You only have one chimney.

Ciao,

Marcel

[aikitarik]

Originally Posted by Marcel

#78

(M) Tarik, did you mortar the re-bar to the inside, or outside of your clay liners? __________

Rebar? Good idea. I guess I could mortar some rebar to the outside. I've only got two pieces on so far until I finish my roof.

(M) I have a thought for a temporary chimney roof. Consider cutting the 5th liner (if you have an extra) on the diagonal with your angle grinder masonry blade. That should produce 2 ninety degree tile roofs that you may be able to balance over the opening until you decide on something more decorative. If you leave some of the adjacent corner edges you'd have one roof too small but the larger one would look more finished. You only have one chimney.

Interesting idea. I'll ponder it. In the meantime, checkout http://www.designtoscano.com for dragons!

[aikitarik]

Marcel,

I have only 2 segments of chimney flue stacked in place currently, with refactory mortar holding them together and no reinforcement or bracing. It is my intention to build a cage around them out of the steel studs and somehow connect the chimney flue to the cage.

The idea of mortaring in rebar as reinforcement, especially here near the epicenter of the 1989 Loma Prieta is entirely logical and I'll probably do something of that sort, perhaps drilling a few holes to drop the rebar into. I wouldn't place rebar on the inside of the flue pieces simply because of the caustic (and moist) nature of the smoke and offgased chemicals from burning wood which would lead to rapid rusting.

Sorry if I was unclear earlier.

[janprimus]

Originally Posted by aikitarik

I wouldn't place rebar on the inside of the flue pieces simply because of the caustic (and moist) nature of the smoke and offgased chemicals from burning wood which would lead to rapid rusting.

IMHO
Actually, the creosote from the smoke would envelop and I would wager somewhat preserve the rebar located within the flue. It gets quite a sticky almost waxy buildup on it.
Chad

[aikitarik]

Originally Posted by janprimus

IMHO
Actually, the creosote from the smoke would envelop and I would wager somewhat preserve the rebar located within the flue. It gets quite a sticky almost waxy buildup on it.
Chad

So you would recommend rebar mortared along the inside of the chimney flue?

[janprimus]

I dont know that I recommend it or not, I was just saying I didnt think it would rust. Did you ever see a rusty piece of smoked salmon? ;-P
My main concern is the differing rates of expansion and contraction of the flue tiles vs the rebar. I think this is why they cannot put reinforcing metal in refractory cement because of the differing rates of expansion which would certainly cause the material to crack. Perhaps if it were epoxied somehow or epoxy in the mortar... I just dont know how it would stick. The more I think of it the less it sounds like a great scheme.