When are cracks acceptable?

[Microheli]

I fired up my my brick Pizza oven for the 1st time last night. The oven has a a brick dome with a 2 inch coat of the correct cement. I noticed some exterior cracks two hours into the burn. The cracks were emiting steam like vapor. the interior has no cracks.

This morning I could notice the cracks had some kind of white calcium residue.

Is this normal?

Today after I started heating the oven, I noticed the oven entrance has some cracks along the brick cement joints.

I am worried, am I doing somthing wrong?

After 5 days of heating the oven I was plan to cover the exterior dome with insulation and later regular cement and some decorations.

Should I be doing somthing diffrent?

[brickie in oz]

Sounds like the oven is still wet, did you go through the curing process?

[cholme]

I assume when you say you fired it up, that you are either on the first low temp curing fires? Cracks will occur for a couple reasons. First, if the concrete dried to quickly after the initial pour. i.e. If the air temperature was such that the concrete dried before curing. It is recommended that you keep it moist for a week or so.

The second way to ensure cracks is to start too hot a fire too fast when there is still moisture in the concrete.

Hairline cracks are to be expected, but it you are getting smoke through some of them, you will probably want to patch those.

[Microheli]

The oven is currently in the curing process 2nd day 07/24/2011.

Today I found some hairline cracks in the arch; I am kind of worried that the arch might collapse. Thank you for you're feedback.

[cholme]

Not that it matters at this point, but did you soak the bricks before you mortared them? If your bricks were dry, they will leech out the water in the mortar and won't cure properly. I am not experienced enough to recommend a fix for this. Perhaps some of the Master Builders will chime in for you.

I do think you should address it, those look like more than hairline cracks to me.

[brickie in oz]

Originally Posted by cholme

Not that it matters at this point, but did you soak the bricks before you mortared them? If your bricks were dry, they will leech out the water in the mortar and won't cure properly.

Not true actually.
As Ive stated many times, we lay bricks in 30+deg c with no ill effects to the mortar.

The cracks look as if the fire got too hot too quickly.
Plus the lack of buttressing for the arch wouldnt have helped, as the arch heated up is spread and tried to flatten out.

[Microheli]

I agree, the fire did get to hot and to quickly in the arch area. Is there anything I can do? Can I just leave it like that? Is there a thin compound that could be poured in the cracked area? Is there a risk of the Chimney area falling?

[brickie in oz]

Originally Posted by Microheli

Is there a risk of the Chimney area falling?

Wider shot pics are needed to tell that.

If its not too bad you can dig out the mortar and bog it up again with a mortar slurry.

[cholme]

Not true actually.
As Ive stated many times, we lay bricks in 30+deg c with no ill effects to the mortar.

I stand corrected. I am not a brick mason... just going on what I have heard and read. The spreading makes sense. Is it too late to add a buttress to your arch support? Perhaps something made of angle iron if space is an issue.

[Johnny the oven man]

Arch-bricks would have been a better option, with less gap.
As it stands, those bricks appear to be able to just fall out, there is no "wedge" to hold them in place.