36 inch oven dome cracked

[Mexman]

I just rebuilt my oven dome and spent a week building small fires. When I got it up to 800 degrees , the dome cracked in several places. I know I didn't wait long enough for it it to properly cure.
My question, when I repair the cracks, should I heat the oven up to 800 degrees because I noticed, the cracks get bigger (wider) when the dome is hot.
What's the best way to repair the cracks?

[Novaslo]

Re: 36 inch oven dome cracked

Seems like the outershell cracks are no big deal, do you have tight brick joints inside?

What does the inside look like?

[Mexman]

Re: 36 inch oven dome cracked

As far as I can tell, the inside is good. No visible cracks.

[Gulf]

Re: 36 inch oven dome cracked

Mexman,

Can you back up, and let us know if your pic is of a cladding applied directly to the firebrick dome. Or, is this a pic of a masonry render over insulation? To me, it appears to be a render over vcrete or something similar. If so, is there a blanket layer in between the firebrick and the vcrete?

[Tscarborough]

Re: 36 inch oven dome cracked

Unless smoke is coming from the cracks or that is your final finish, do nothing.

[Mexman]

Re: 36 inch oven dome cracked

Mexman,

Can you back up, and let us know if your pic is of a cladding applied directly to the firebrick dome. Or, is this a pic of a masonry render over insulation? To me, it appears to be a render over vcrete or something similar. If so, is there a blanket layer in between the firebrick and the vcrete?

It's a picture of a render over two inches of vermiculite. Steam was coming out of the cracks the first two times I baked a pizza. There's nothing coming out now. My contractor suggested that we fill the cracks with a glue he has for tile.

[Gulf]

Re: 36 inch oven dome cracked

It's a picture of a render over two inches of vermiculite. Steam was coming out of the cracks the first two times I baked a pizza. There's nothing coming out now. My contractor suggested that we fill the cracks with a glue he has for tile.

So, is that the only insulation that you have between your dome and your render?

Vermicrete will swell and relax until it is dry. The firebrick dome will swell and relax with heat cycling. Though, not quite as much. Unless the vermicrete insulation is allowed to dry completely before it is heated to to full operating temp, it helps to have a blanket in between the two shells. Not only to act as first line insulator, but also as an expansion joint between the two. That in itself, may not be enough, if steam is not allowed to escape. A vent (or a temporary vent) at the apex of the dome may help relieve moisture from the build, and also, later moisture from natural humidity.

At the very least, don't seal those outside cracks until you are sure that all extra moisture has been eliminated. You can see steam escaping, but only in massive amounts. Use the "clear plastic technique by David S to ensure that it is completely dry.

[Mexman]

Re: 36 inch oven dome cracked

Thanks Gulf
What is the "clear plastic" tech you mention?
I have a tarp over the oven right now to keep the rain from getting into the cracks. I've been bringing the oven up to full temp about ever three days and I think I have it dried out.
I need a little more insulation on the dome and looking for a two inch ceramic blanket here in my area in Mexico. The dome is cool ( around 80 degrees) except a small area where the flame hits the dome. It over 150 degrees in a two foot sq area.

[Gulf]

Re: 36 inch oven dome cracked

Any clear plastic that you can place over the dome will do. It allows you to see the water droplets forming underneath the plastic from steam condensation during firing. This is a pic of a piece of plastic (I think it was part of a dry cleaning bag) placed over a vent hole that I had purposefully left at the apex of the dome. The shell will be hotter in any area that has not fully dried. In my case, that area became an increasingly smaller area at the very apex of the dome. When it was totally dry, the entire outside shell was closer to ambient temperatures. I'm not saying that you don't need more insulation. But, I would keep the drying fires going until I was sure that all moisture had been driven out.

[Mexman]

Re: 36 inch oven dome cracked

I have my oven covered with a blue tarp to keep the rain out of the cracks. I notice the dome has wet spots even without a fire in the oven. I figured it was condensation during the night.
I assume you are talking about wet spots while heating the oven.