How much crack is too much crack?

[aikitarik]

My oven cracked during our first firing (not a hot enough to burn the soot off fire) after more than a week of curing.

NBD, I think, because everyone has said that their oven has cracked and will crack. YOu could literally see the moisture along the crack lines. But my concern is twofold... how much is too much?

1) the dome is quite sturdy, but it cracked enough to let smoke out.. also it cracked all around the oven showing fracture lines front and back... when I patch, do I use the same mortar and do I worry about the structural stability in the long run?

2) my front archway, which will be covered up was only a few days old, so it cracked enough that I can probably lift out the keystone... that's just a lesson learned about rushing the heat..

Do I have to start over? *snif*

[Bob C]

Tarik,

I believe I read somewhere that furnace cement in a caulking gun application should do the trick...I am fortunate not to have any cracks that big...(no smoke) but plenty of hairline cracks.

Lets see what the experts say before you use my advice.

Otherwise I would feel obligated to travel cross country to build another oven . Really, I dont believe there is much to be concerned with as long as bricks are secure.

Bob

[Marcel]

Wise cracks

#54


(AT) My oven cracked during our first firing (not a hot enough to burn the soot off fire) after more than a week of curing.

(AT) NBD, I think, because everyone has said that their oven has cracked and will crack. YOu could literally see the moisture along the crack lines. But my concern is twofold... how much is too much?

(M) From what I've read, your dome has considerable structural integrity so collapse would not be my concern.

(AT) 1) the dome is quite sturdy, but it cracked enough to let smoke out.. also it cracked all around the oven showing fracture lines front and back... when I patch, do I use the same mortar and do I worry about the structural stability in the long run?

(M) If it were mine ( which will also crack, and far worse than yours!) I would not add more mass by way of refrctory mortar. I would put another? coat of perlcrete over the entire dome, as well as what you can reach of the chimney manifold, and even the chimney itself, to seal those wise cracks.

(AT) 2) my front archway, which will be covered up was only a few days old, so it cracked enough that I can probably lift out the keystone... that's just a lesson learned about rushing the heat..

(M) I went to your Photos on Yahoo and I believe it was #066 that shows the completed dome with a coat of some kind of masonry. It appears to be refractory mortar. Is that what I saw? ___ If so, I suspect that it is considerable less "elastic" than perlcrete. Consider also the advantage of insulation you'd get from Perlcrete.

(M) Are those great kids in photo # 070 yours? You need nothing more to round out your life!

(AT) Do I have to start over? *snif* [img]file:///C:/DOCUME%7E1/MARCEL/LOCALS%7E1/TEMP/moz-screenshot-66.jpg[/img]

(M) You better *not*! Try to think of this project as a process. You and many others, like Paul and me, are simply in the middle? of that process. Enjoy it and try not to be disheartened. I know that's easier said than done as I view my badly asymetrical dome, but, ... that's why they call it life.

Ciao,

Marcel

(M) P.S. What is "NBD" ? ___

[svtlightning]

Tarik
You'll be fine and so will your oven.
Furnace cement in the tube will do the trick to seal the cracks and set the keystone. I got it at Home Depot, couple bucks. I used it to set the flue liners and it setup strong.
Mike

[james]

Tarik,

Sorry to hear about the crack. As others have said -- your oven will be great. I have had good experiences with fireplace chalk as well. It sets when it gets hot.

I have only found black. Does it exist in other colors?

James

[Marcel]

Furnace Cement for flue liners, & Mossarella

"You'll be fine and so will your oven.
Furnace cement in the tube will do the trick to seal the cracks and set the keystone. I got it at Home Depot, couple bucks. I used it to set the flue liners and it setup strong.
Mike

#55

Hey Mike,

(M) I was unable to find flue liners in lengths greater than one foot so that's what I'm going to use; 5 of them! Jim Hatch's oven looks like he found at least a 3' piece, but on another photo, it looks as though he added a section and I'm wondering what he used? ___

(M) Jim,if you're reading this, please provide your input, too. ___

(M) MIke, are you suggesting that I use "furnace cement" rather than self made refractory mortar to join these one foot sections? ____ If so, how thick a bead should I use? ___

================================================== =====

(M) "Mossarella" indeed, ........ shame on you

(M) Grass ias for your input.


Marcel

[svtlightning]

Marcel

I used the furnace cement in the caulking tube, it dried dark greyish in color.
I just layed a bead the thickness of the liner wall.
My local masonry supply only had 2' in lenght flue sections. They had many differnt cross section sizes in stock. My oven seems to be working well with the 2' sections.

Mike

P.S.
Quit beating yourself over the irregular dome courses. Just keep moving on and it will work out. These ovens can handle alot of variations of design and construction.

[aikitarik]

Thanks, all..

I knew it would crack, I just didn't realize how much. The guys I talked to at our local rock and refactory supplier all said that the locally made ovens they've seen all show cracks and sometimes even a little smoke when going full blast and they're fine. They told me about one local oven that looks like a spiderweb of cracks when it's fully heated, all of which vanish when the oven cools.

They didn't even recommend (or NOT recommend) patching with furnace or refactory cement, which they sell by the bucket instead of tube. Left it up to me. I'll patch the areas that are extreme, but not worry about the rest.

I picked up the steel studs to make my framing and I'm going to use 8.5x13 flue lines for my chimney/vent. Next step is probably coating the oven with perl-crete to insulate things and framing things up! I am trying to figure out a way to leave a hinged lid in the roof so I can get in to perform repairs if needed in the future.

Thanks, again!

[aikitarik]

#54
(M) If it were mine ( which will also crack, and far worse than yours!) I would not add more mass by way of refrctory mortar. I would put another? coat of perlcrete over the entire dome, as well as what you can reach of the chimney manifold, and even the chimney itself, to seal those wise cracks.

This is what I intend!

(M) I went to your Photos on Yahoo and I believe it was #066 that shows the completed dome with a coat of some kind of masonry. It appears to be refractory mortar. Is that what I saw? ___ If so, I suspect that it is considerable less "elastic" than perlcrete. Consider also the advantage of insulation you'd get from Perlcrete.

It's the normal mortar with fireclay we used. No layers of percrete yet.

(M) Are those great kids in photo # 070 yours? You need nothing more to round out your life!

My nephew and neice! They're wonderful... we have none of our own yet.

(M) You better *not*! Try to think of this project as a process. You and many others, like Paul and me, are simply in the middle? of that process. Enjoy it and try not to be disheartened. I know that's easier said than done as I view my badly asymetrical dome, but, ... that's why they call it life.

I am a martial arts student, so I know a lot about process.

Regards,

Tarik

(M) P.S. What is "NBD" ? ___

NBD = No Big Deal

[aikitarik]

Fwiw...

...I patched the cracks in the oven with a tube of refactory mortar during another fire (not as hot! ) and plan to do so again at full burn before we insulate the oven. Seems to work well.

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.

Tarik

[Marcel]

# 58 "If it ain't broke, don't fix it"

#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]

Chimney cap

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]

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]

Re-bar in or outside flue liners? & Temporary roof

#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