Planning my 32" cast oven

[AndreasP]

gnwjr
We had some unexpected rain last week. 0.22 inches overnight, so actual rain, not just a sprinkle.
Made pizza yesterday and the oven worked just fine. Didn't notice a difference, so for now I think the waterproofing is working.

[gnwjr]

Excellent! It’s looking like I’ll be using your waterproofing technique as well. Do you have a source for the breather vents?

Thanks

[AndreasP]

I bought it at Grainger, it's the only place I found a screw in vent. 3/4 I'm NPT, so it fits a copper screw fitting.
I feel it's a bit big so I'm looking for something smaller.

Maybe just close it up completely, since the vermicrete is exposed around the chimney below the flashing at the bottom.
Then again, probably not a ad idea to have an opening on the tallest point of the dome.

[UtahBeehiver]

Most autoparts store carry breather caps. You can use a 1/2" pvc bushing with 1/2" mpt plastic breather valve. See Gulfs build.

[evo]

hey could you share please how long it takes to heat it up and how long it retains the heat for?

[AndreasP]

It takes me about 2 - 2 1/2 hrs to heat up and have the dome completely cleared. I find that waiting another half hour hour or so makes for easier pizza baking and a more consistent heat. So typically I start 3 hrs before I want to make pizza.

As far as heat retention, I have an insulated door, but it doesn't have a gasket, so I think there may be some heat loss around the edges.
The temperature I get depends a lot on how hot the oven was when I started. It takes a lot of wood to keep the oven at 900F, and we often do desert pizza when we are done with the normal pizza.
I find that after 12 hrs. I am around 450 or so, a bit too cold for baking baguette. But not too difficult to heat it up again if I need to.
I am sure I could also improve the temperature by making another large fire when I am done with pizza, but then again, I might just as well make a fire the next day.
It would be nice to have the oven at 550 after 15 hrs or so, what would allow me to get up in the morning, finish the bread and bake it in the oven around noon).

Attached is a graph from 4 different firings. Of course the graphs are a bit offset based on the starting temp, but they provide a good idea of what is going on. I simply fit an exponential decay to the points.

[david s]

Now you've caught the oven building and cooking bug, when are you going to build the next oven?
You've done a fantastic job for your first one and thanks for sharing your journey. One of the greatest things about this forum is that folk are keen to share all their secrets documenting experience and experimentation for the benefit of others. It's a wonderful opportunity kindly provided by our Forno Bravo hosts.

"Fire turns man into a philosopher"

[AndreasP]

David, yes, I completely agree. Without the help from this forum my oven would never have turned out the way it did.

Not planning on building another one for now though, unless we move (no plans there). It's a lot of work and I have run out of space. This oven was already quite the squeeze.

[david s]

I was thinking you might want to help a friend build one.

[AndreasP]

I would certainly do that, but at the moment they are all just coming to our house to have pizza.

[AndreasP]

Had another pizza gathering last weekend.
I Keep having problems with smoke coming out the front opening, especially while firing up the oven (first half hour or so). I do light the fire in the entrance underneath the chimney to get the draft going for a few minutes.
How long do others keep the fire there?

I think my 3ft chimney could be a bit taller, it is 6" diameter, but I didn't really want it to stick up over the fence, and adding an extension would not look very nice.

Last weekend it a bit breezy, so I placed the door on top of some bricks so that there is a small gap at the bottom. This forced the smoke through the chimney and seemed to work really well.

I think I used less wood to heat the oven and the oven was ready a bit faster (kind of makes sense with the door added).

I attached a picture.

Any thoughts on if this is a good or bad idea? Any concerns?

Andreas

[fox]

Is your chimney insulated?

[david s]

Reducing the air intake will take the fuel:air mixture closer to optimum which will send the temperature rise soaring to around 300C/hr. This would be the equivalent of firing a kiln at full blast from ambient, which results in damage to the wares inside as well as straining the kiln’s refractory. The reason is that the temperature difference and resulting thermal expansion difference produces stresses that can result in micro (ones you can’t see) and macro cracking. Far better for the longevity of your oven (or kiln), to fire slowly (200C/hr) which allows the heat to penetrate slower without subjecting the refractory to excessive thermal expansion differences.

Regarding your smoke issues, you may find that simply keeping the fire quite small for the first 1/2 hr will prevent the smoke escaping. I learnt this technique years ago when I was at a market stall and the woman beside me had lots of hand knitted baby ware. Smoking them out was a serious concern, but keeping the fire quite small at start up worked well.

[AndreasP]

My chiney is a simple double walled chimney, not insulated.

I currently use the top down method with a big stack that barely fits through the entrance. I'll try the small fire to see how it works.

I guess I'm happy I only added the door once the ceiling started clearing and tried to see how to keep the smoke from coming out the door.

In the end it's not that big a deal. I use Avocado and pine to start the oven and get it to temperature (free wood).

When I cook pizza I use almond wood which really doesn't seem to smoke (and wasn't free).

Thanks for all your help!

[Kris S]

I don't use pine because it tends to give off a lot of smoke, which I noticed using our wood stove...

Pine tends to smoke a lot especially on igniting when the fire's not very hot yet, and even more so when you shove a whole load in the oven at once.
I also use the top down method to ignite the oven (and wood stove), but just a small bundle of wood to start with (in the centre, not under the entrance) and feed it a couple of sticks at a time until I have a big fire. with this method only the first 10 minutes there's some smoke that escapes, after that none at all.