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Jonathan Hart 09-17-2007 03:54 PM

Cracks with smoke coming from them
I cured my oven and had many small to medium fires before I fired it fully and had pizza the other night. I have several small cracks that are leaking smoke when the oven is at cooking temp. The cracks first appeared after the first firing and continued to grow every time the oven was fired.
They are just big enough to see a sliver-- and I mean a sliver-- of fire through them and no longer then 3 inches.

What do I do to repair them and what do I repair them with? Is my oven ruined? Oh, it isn't insulated yet and I used the fireclay mortar if that helps..?

Thanks- Jonathan

PS- The pizza was great!

james 09-17-2007 05:25 PM

Re: Cracks with smoke coming from them
Hey Jonathan,

They all crack! :-) It happened to me. There are various approaches to closing them off. I used refrectory mortar to close in hairline cracks in my vent. If you can push enough mortar to will the gaps, and let that air dry, then put another layer our two around that, and let it all air dry, that should do it. Also, you will want to cure the oven slowly again.

What would other folks add? How did you repair your crack?

telehort 09-17-2007 05:31 PM

Re: Cracks with smoke coming from them
I had a crack that I could see a small amount of light through. I did as James mentioned and tried to work as much mortar into the crack as I could, let it dry and put another layer over that..let dry and re cure and it appears to have worked.

Ken524 09-17-2007 06:18 PM

Re: Cracks with smoke coming from them
Will curing the oven after insulating reduce the chances of cracking?

Bacterium 09-17-2007 07:06 PM

Re: Cracks with smoke coming from them

Originally Posted by james (Post 15364)
Hey Jonathan,

They all crack! :-) It happened to me.

so true.....

Jonathan I would say cracks on the inner layer are less of an issue. From experience I believe the insulating layer is where you want to achieve the absolute minimal cracking possible.
My thoughts.....if heat escapes from the inner layer(via small cracks) it will just hit the insulating layer which theoretcally should hold it in and reflect back into the inner layer.

Sure you want the inner layer nice and properly fitting so that it is all keyed together (most important).....however - remember this area undergoes the largest variation in heat, so therefore the largest expansion/contraction range

Now, for something slightly off topic but may come into play......and I'm still working on the detail as I explore options.
My outer layer has 2 cracks (render/stucco coat) that concern me a little - sure don't let any heat out but my concern is moisture ingress - meaning that it may let rain in there which may add problems as far as long term integrity. These cracks appear to open/close ever so slightly - everytime I use my oven. So in actual fact its like an expansion gap - things get hot and they expand - crack opens(max. 1/8th of an inch). It cools down and therefore it closes. If I put a mortar in these cracks it will be rigid and effectively just keep pushing it open/close with expansion/contraction.
Now I wish to seal my outer layer (succo/render coat) with a style of conrete sealer so that it stops mould growth(keeps the oven exterior looking all nice and tidy). I'm hoping to find a flexible coating that will not only inhibit mould growth but also dribble down into the cracks and provide some kind of flexible moisture barrier. My quess is the crack is not something you can stop so I will turn it into an expansion joint.......intestingly enough the cracks are on opposing sides of the dome - its as though the whole things stretches in 2 halves and then closes.

Les 09-17-2007 08:02 PM

Re: Cracks with smoke coming from them

What type of stucco did you use? I understand that there is an acrylic base product that is bullet proof. I haven't shopped for it yet because my shop is still full of sand, portland cement, lime, clay, heatstop 50, etc... :( It seems to me that the blanket(s) should more than accommodate the expansion.

Appreciate you feedback.


Jonathan Hart 09-17-2007 08:44 PM

Re: Cracks with smoke coming from them
GLad to hear that they all crack! I had that sinking feeling that all my hard work was for naught! I was thinking about jamming a mixture of fireclay and water down the cracks and then mortaring over it and calling it good. I figure the clay is very impervious to heat and I just need something to keep the fire and gases in the oven and and not to further hold the oven together.

Thanks again for all the input. Seeing your oven crack after all the hard work was a little troubling.


Bacterium 09-17-2007 08:53 PM

Re: Cracks with smoke coming from them
For the stucco (or as us Aussies call it "render") I did my own mix of washed sand and portland cement (+ small amount of oxide for colouring). I looked at some local acrylic based stuff and it seemed there was no quarantee that there would be no cracks unless I incorporated some form of expansion gap (by the way I read it)......I was under the understanding due to the oven dome area and its shape it would need one..........So in the end I figured I would just apply a final texture coating (after some months of use) over the whole lot once any cracks appeared and oven settled down.

what are other peoples experienced with exposed domes, have they successfully used acrylic based stucco's and not had cracking?

james 09-17-2007 08:56 PM

Re: Cracks with smoke coming from them

Make sure you use a complete refractory mortar when you pack the cracks. You need to make sure that is sets hard, and that it doesn't fall in later.

tom75gkp 10-05-2008 05:40 AM

Re: Cracks with smoke coming from them
Hi all,

I'm interested and somewhat relieved to see that I'm not the only one with cracks in my newly built dome. The cracks I have are hairline when the oven is cool but expand to around 3/16ths of an inch when the oven is fired. At first I thought that I was seeing smoke from them but I think it is actually steam. I am firing it again at the moment and the steam is rising. When the steam stops I plan to fill an empty mastic tube with fireclay and try to inject it the best I can into the cracks. Anyone out there with a similar experience?

Once I have fixed the cracks I plan to finish the oven with a gabled house look and terracotta tiles.

I am also trying to source an infra-red thermometer, anyone know of a supplier in the UK?

I'll try and post some photos of the oven and would be interested in any suggestions anyone has for improvement.

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