My first WFO design, any comments before I build?

[Mark1986]

Update 3 years later..

So I didn't do much to my oven in the last years. I used it a couple of times but it was quite a lot of work getting it on temperature en not smoking out the whol neigbourhood..

This year I decided I wanted to finish my oven:

1. Remove the chimney from the cast
2. Reattach it on top of the cast
3. Put on render so I can paint the oven
4. Add reinforcement to the wooden stand under the oven

So I'm almost done with point 1 and 3.


I removed the flue:



Made a cast for the flue. Its a bit more narrow than the flue itself. I will grind it down once the new flue is on top:


I put render on the dome of the oven. It turned out a bit rough. But I will sand it down and fill some of the rough patches:



david s

fox


I have a question. I just went for filling up the flue gallery (right term?), like you see in the picture. Now I didnt really think this out on how I put the new flue on top and make a joint. Would you have any recommendations?

I can't put it on top and just use a heat resistent adhesive kit. That wouldn't be strong enough..

I though about making a cast on top, just a bit wider then the flue. Then put it in and fill it up with heat resistant kit.

Advice would be much appreciated!

Best,


Mark

[fox]

You could make a few expansion cuts with a mini grinder inside the chimney pipe or even better remove that pipe and fit a 150mm pipe on top of the opening.
That Vitcas silicone is ok in none flame path locations, it is not a hard setting silicone but is a good product for sealing certain components.

[Mark1986]

david s I think I'l let the cracks inside the dome for what they are. They don't bother me..

The crack on the front that was caused by the expanding and contracting flue pipe is something I would like to fix though. I was thinking about drilling a space around the flue pipe entry in the opening of the oven and fill it with heat-resistant sealant. Is this how you would go about doing it?

[david s]

Ok, give it a try, but filling cracks is rarely successful. Generally once they’re there then thy are there to stay.

[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!

[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]

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!

[Mark1986]

david s

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

[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!

[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]

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!

[fox]

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

[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]

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]

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?