New Oven, smoke leaking when curing

[midlife]

Hi There

I'm Jon. I've recently finished an oven project, pics attached. It was 2 years in the planning (and saving!) and has taken 3 years to build on and off. It was designed and built myself with the help of my Father in Law. I'm an office worker by trade and this has been a steep (but enjoyable) learning curve and resources such as this forum have been invaluable. Any criticisms or comments would be gratefully received. I know it's quite close to a wooden fence but with a small Garden I had little choice and I figured some people have these indoors so it should be OK!!

My main reason for posting is because I've started the curing process over the last week, firing it for a few hours each day and slowly building it up. On the 4th day and the most intense fire yet I noticed some smoke leaking from the bottom of the exposed chimney section where it meets the metal dome. The last picture on the attached pdf shows where I mean. You can see the silicon has lifted, maybe due to metal expansion with the heat but it should still be sealed under there so I think I'll need to re-do the top chimney section at least. But that sounds like a job for the Spring and I wondered if anyone could tell me if smoke leaking under the dome is a safety issue? Has anyone else covered their oven with metal?

Many thanks

Jon

Attachments:

Presentation2.pdf (1.11 MB)

[oblertone]

Hi Jon and welcome; that certainly is a different build but extremely neat and I personally love the metal dome which I've never seen before, was it a custom built for your project?

As for your smoke issue, it's hard to see where the 'smoke' could be generated unless it is coming through the joint of your preformed dome. You will get some smoke issuing from the front entrance when in use despite there being a flue in place, so I'd reseal the joint and just use it as is. Trust me, no-one but you will notice.

Most curing regimes are intended to drive water from the structure, however your is a preformed dome covered by vermiculite and insulating mat, neither of which contain water. Given that the gap between dome and exterior wall is filled with insulation I'd be surprised if that got hot at all, and certainly won't need curing in the conventional sense of the term.

The only cautionary note I would have is the seal between the brickwork and your metal cover needs to be sufficient to stop your insulation getting wet.

[midlife]

Thank you for the reply.

The dome is actually a fire pit from www.roundwood.com . My father in law spot welded the drainage holes and drilled the chimney hole. I then had a local company powder coat it for me.

I think the smoke leak is coming from where the top vertical section of chimney meets the dome. I was concerned that build up of smoke under the dome might be an issue? I plan to fix it but wanted to keep firing it in the meantime?

Interesting point about curing not being such an issue. Every day's a school day!

I've used standard outdoor silicon where the dome meets the bricks

I've taken hundreds of photos of the build and would be happy to post if anyone would find it useful. Learnt a lot about concrete worktops along the way as well.

Thanks again

Jon

[simonh]

looks great, I would be surprised if it was smoke from the oven escaping there, are you sure it is not the silicon itself overheating (the chimney will get pretty hot)

Simon

[midlife]

Hi Simon

Thank you for this. Interesting thought. The silicon used on the top of the dome was fire rated to 1000 degrees (it's only around the sides where the dome sits on the bricks where I've used standard exterior silicon). Also there was quite a lot of smoke so I'd be surprised if that was the cause. The last chimney piece had to go after the dome was fitted because of the flange. The only thing holding it in place is silicon so I think I may have to lift it off and figure out to rivet it or something?

[downunderdave]

Hi Jon,

My immediate thought is that it is your high temp silicon burning. You say it is rated to 1000 degrees. I presume that is F. The highest rated silicon I can find is Permatex Ultra Copper which is rated to 700 F (371 C) intermittent. The heat from an oven can scarcely be called intermittent. I use it between the ss flue pipe and its seal which is similar to your set up in that it is well above where the flue pipe meets the inner oven.The stuff is only just adequate for my oven design. If you used a product that remains flexible to 1000 C I'd love to know what it is.
Another consideration is that the excessive moisture in the oven during the drying fires can create steam which may be mistaken for smoke.
Another possibility is that smoke is leaking between the stainless pipe and the flue gallery.
Also you say that the steel dome has been powder coated. I don't know what temperature they use for this process but it may we'll be lower than what you are subjecting it to and therefore the powder coat may be burning.Can you hold your hand comfortably to the outside of the steel dome?

[downunderdave]

See "What are the maximum service temperatures?"

www.cjponyparts.com/skin/frontend/cj-pony/default/images/install-pdf/install_pc-v.pdfbd

[jagnut]

Jan 28, 2018 11:10:33 GMT downunderdave said:

See "What are the maximum service temperatures?"

www.cjponyparts.com/skin/frontend/cj-pony/default/images/install-pdf/install_pc-v.pdfbd

Sorry downunderdave for interrupting this post i have just seen the photos on this build and i must say it looks fantastic .One problem with using steel in this way is condensation to the under side of dome , the next easy fix to the silicone on the top of the dome is straight forward because your dome is steel and the flue is stainless steel the expansion rate are different ,the best way to over come this is to use flat sided fire rope and sandwich it between dome and flue pipe top.  Then fix with stainless steel pk screws (self tapping screws ) .This way will act like a expansion joint  and flex with different temperatures ,you will have to also allow for changes in ambient temperature being a steel dome .

[downunderdave]

I think there is sufficient elasticity in the silicon to cope with any difference in expansion rates. Pics show my set up and although it no longer looks pretty the silicon there is still good after 10 years. The reason I said the high temp silicon is "only just adequate" is that in my mobile oven design which I hire out frequently, I have had to redo the silicon about three times. The difference is that sometimes when people hire my mobile oven they obviously want to see how high they can get the temperature gauge. This probably means big flame up the flue and the silicon can't take the extra heat. The two terracotta caps in my design also allow steam to escape between them as they're not a perfect fit. Re condensation, there will be water condensing where any moist hot air meets a cold surface whether it be steel, fibreglass or concrete.
I think your build is beautiful and you should keep firing it and you'll nut out the problem.

[midlife]

Hi There. Thank you so much for the replies and sorry for the delayed response. I have a newborn and have been somewhat preoccupied the last few months!!

That's great advice on the firerope. Here's the silicone I used;

www.glowing-embers.co.uk/ChimneyAndFlues/FlueAccessories/HighTemperatureSealants/EnvirografSiliconeSealantHeatResistantUpTo1200degC

I must admit I have been concerned that the metal dome doesn't allow the oven to "breathe" and that moisture could get trapped but I'm certain it's smoke and not steam escaping.

As for the powder coating, I fired it up to full temperature for the first time at the weekend. Took almost 2 hours for the inside of the dome to go white. Cooked Pizza in 90 seconds and it was delicious, pic attached. The dome did get very hot to the touch but it was a very sunny day which I'm sure contributed. On the hottest part I had to take away my hand after about 1 second. If the powder coating fails then I'll have to come with an alternative covering. It would be a shame but not the end of the world. Just an expensive mistake!