My first WFO design, any comments before I build?

[Mark1986]

I have started curing the oven since yesterday starting with small fires. I did this for three hours and there were no cracks. You can see it in the photos below.



One thing that did startle me a bit was the amount of smoke and the smell of it. I wouldn't want this to be a problem with my neighbors and girlfriend. Do you think this problem will go away if I start making hotter fires? I'm also wondering if my flue is large enough. Dimensions of the oven and flue:

- chamber > 65 cm wide and 32.5 cm heigh
- Flue/chimney > 12cm wide and 50cm heigh (from opening ceiling)

I'm also thinking about making two doors, one for closing the front and one for closing the oven chamber. Last one will be hard as I didn't make a ledge for it to stop on.

Any advice?

[fox]

Re the smoke and smell… the smoke will be burnt away inside the dome on route out of the chimney but not until the oven is dry and functioning properly at high temperature .
Re the drying fires … it does take time and patience but is very important to go nice and slow if you dont want to many cracks!

There are many ways to go about drying the oven, lots of small fires gradually getting bigger over 5-7 days is pretty standard

Personally I always start with a BBQ brickettes suspended off the floor on a baking rack or similar. I start with only 5-6 bickettes and buildup the amount and time over the first two days.
Then begin the fires, if possible I keep the fire going for a few hour's in the morning , let it cool and do more fires in the evening so quite time consuming !

[Mark1986]

Re the smoke and smell… the smoke will be burnt away inside the dome on route out of the chimney but not until the oven is dry and functioning properly at high temperature .
Re the drying fires … it does take time and patience but is very important to go nice and slow if you dont want to many cracks!

Can you also comment on the flue width and height? I'm a bit worried that I might messed up with the size..

There are many ways to go about drying the oven, lots of small fires gradually getting bigger over 5-7 days is pretty standard

Personally I always start with a BBQ brickettes suspended off the floor on a baking rack or similar. I start with only 5-6 bickettes and buildup the amount and time over the first two days.
Then begin the fires, if possible I keep the fire going for a few hour's in the morning , let it cool and do more fires in the evening so quite time consuming !

Thanks for the tips! I follow this video for curing the oven: https://www.youtube.com/watch?v=5cb3aAkU5R8 . I didn't know that you can also use brickettes. I'm going to try that tomorrow!

[fox]

Yes your 120 flue will be fine for a 65 dome although it will work better if it is insulated.
It is quite normal for a new oven to smoke.

Edit ….just looking at you design you may get some smoke escape as there is not really a progressive approach to your chimney or a lip in place so in fact a 6” chimney might of been a better option!
You will just have finish curing the oven and see how it behaves once unto temperature.

[Mark1986]

fox

Yes your 120 flue will be fine for a 65 dome although it will work better if it is insulated.
It is quite normal for a new oven to smoke.

Edit ….just looking at you design you may get some smoke escape as there is not really a progressive approach to your chimney or a lip in place so in fact a 6” chimney might of been a better option!
You will just have finish curing the oven and see how it behaves once unto temperature.

I ordered an extension of 1 meter in height. Would that have a similar effect as having a wider chimney?

[fox]

Well you may be worrying about something that might not be a problem but if it does become an issue there are a few tricks that will help.
I can’t really tell if you pipe is a twin wall, if not then adding a layer of insulation around it will help no end, it may be possible to slip a 9” clay chimney over your pipe and back fill with loose vermiculite, although that might look out of scale!
To be honest if it really becomes an issue you can enlarge the hole and fit a 6” chimney!
You could also make up something that protrudes down from the front lip, just a bit of wood would do.
Like I have already said you need to finish the drying fires before you will know if it is a smoker…

[Mark1986]

Well you may be worrying about something that might not be a problem but if it does become an issue there are a few tricks that will help.
I can’t really tell if you pipe is a twin wall, if not then adding a layer of insulation around it will help no end, it may be possible to slip a 9” clay chimney over your pipe and back fill with loose vermiculite, although that might look out of scale!
To be honest if it really becomes an issue you can enlarge the hole and fit a 6” chimney!
You could also make up something that protrudes down from the front lip, just a bit of wood would do.
Like I have already said you need to finish the drying fires before you will know if it is a smoker…

The chimney is single wall! I didn't know that insulation around the pipe was a thing.. Good to know!

Thanks for the tips, I will first see what happens in the coming days before I decide if I need to take any action

[fox]

Hot air rises so keeping it hot up the chimney will help the draw.

[Mark1986]

david s
@fox

Today I fired up my oven to full heat for the first time and made pizza for the first time. The pizza was a great success (for the first time) and the oven functioned well also.

Video: link
Photo:


Unfortunately, there were also some problems. There is quite a big crack in the center from the flue to the opening of the oven and a small hairline crack in the chamber:



This surely was my fault as I fired up the oven too fast. As a result, there is smoke leaking from the flue opening out to the outside of the flue itself. Is there a way to repair this? Do I have to up it up from the top and use some kind of sealant?

Lastly, I noticed that there is quite a chemical smell coming from the side of the flue where also the smoke is leaking, this is not coming from the oven itself. Could this be the insulation blanket getting too hot from the leaking gasses? This is how it looks under the hood:



Cheers!

[david s]

It looks to me as though you have surrounded the fluepipe with castable. As the pipe is far more conductive than the castable it will expand first creating extreme stress on the refractory that surrounds it. The second two ovens I built both cracked the casting around the flue from this problem, so I now always build them with the flue pipe being a slightly loose fit, with the pipe held in position by vermicrete.

The smell could be the cement or pp fibres if you added them, either way it should disappear with more firings.

[Mark1986]

It looks to me as though you have surrounded the fluepipe with castable. As the pipe is far more conductive than the castable it will expand first creating extreme stress on the refractory that surrounds it. The second two ovens I built both cracked the casting around the flue from this problem, so I now always build them with the flue pipe being a slightly loose fit, with the pipe held in position by vermicrete.

The smell could be the cement or pp fibres if you added them, either way it should disappear with more firings.

Sounds plausible! How would I go about fixing it? I want to make sure there is no smoke leaking from next to the chimney. I am planning to drill from the top layer around the flue to the inner cast and put a thick layer of heat resistant sealant around the flue and the opening in the cast. Or could I just put the sealant at the perlitecrete layer around the flue?

Example:



If I want to fix the front crack in the perlitecrete should I do that with a heat-resistant sealant?

Edit:
I thought about another option. I could also try to seal the flue with a heat resistant sealant from flue opening in the cast from below:



Would that be a better or easier option?

Cheers!

[Mark1986]

david s

I went for sealing it from the bottom inside the pizza oven opening. This worked fine!

[Mark1986]

david s

I used my oven for the second time and cracks did start this time. Here is a video of the crack: video.

And photos:


The crack goes through the center and around the cast that I put on in a second go:


Should I be at all worried about structural issues? If so, how should I fix it?

If it is only cosmetics, how would I fill the cracks?


Cheers!

[david s]

I've not used that Victas product, but the highest temperature rated silicon I can find is Permatex Ultra Copper. If used in that position it will get direct flame impingement and would not survive. What does the Victas product say?

Your oven won't fall down because it's a hemisphere. There are two kinds of oven owners, those who say their ovens have cracks and those whose owners lie about their ovens having cracks.

Did you add polypropylene burnout fibres to your home-brew castable?

[Mark1986]

I've not used that Victas product, but the highest temperature rated silicon I can find is Permatex Ultra Copper. If used in that position it will get direct flame impingement and would not survive. What does the Victas product say?

I found a different one from Bison, don't know if that is a brand you would know.. It is a heat resistant sealant for stoves and chimneys with a rating of max 1250 celsius.

Your oven won't fall down because it's a hemisphere. There are two kinds of oven owners, those who say their ovens have cracks and those whose owners lie about their ovens having cracks.

That is reassuring thanks! Well I will be in the category of those who don't lie about it . At the end of the season I will try to fix it with homebrew, should I try to make a v shape in the cracks before I fill it?

Did you add polypropylene burnout fibres to your home-brew castable?

Yes I think I added about 75 grams per 3:1:1:1 sand:lime ortland:clay batch

Cheers!