42" Pompeii construction in Adelaide

[david s]

G'day All,
David and Mark, many thanks for the feedback.
David, if I may, I'm interested in a little more info on firing the oven insulated as I'm not really grasping the point. Whether insulated or not the firing and heating initially from within the dome through to the outside would surely be the same with or without insulation, after all the bricks will be the same temp throughout when starting the fire?? What am I missing here? Also, how would one know the extent or degree of cracking if the dome is covered?
Mark, cracking as shown in photo's. No detectable heat rise using a heat gun near the cracks suggesting no hot air is escaping, and the last fire was real hot. I do have 2 minor cracks through the inner arch along joints at the top, not shown in photo's, very minor.
Thanks again, it's all great info.
Kind Regards
Greg

Hi Greg,
The accompanying video explains what happens if a clay flue tile is heated when uninsulated. Being thin makes the likelihood of failure much higher, however the same principle remains. It is the difference between the temperature of the inner and outer surfaces that leads to a difference in thermal expansion that leads to failure.

https://www.bing.com/videos/search?q...tail&FORM=VIRE

[P3 Stoaker]

G’day all. Google assisted, the apex is the top.
Can anyone see why the vent can’t be at the back towards the bottom?
Also, anyone got any good ideas how to best seal the render at the bottom of the dome? My oven is outside and therefore want to prevent water getting in under the render. I an laying bluestone slabs around the oven on the hearth and have them slopes away but water is likely to ‘wick’ in.
Regards
greg.

[JRPizza]

I didn't need one. I cured without insulation and got a few internal cracks big enough to let any steam out

[P3 Stoaker]

G'day All,
I'm looking at insulating the dome soon and wondering about location of a breather. I see a lot of recommendations to position the breather at the apex of the dome. Could someone please explain where that is?
Does it even matter where the breather is? It's only letting any pressure out right?
David S and Mark Jerling, not sure if you saw couple questions in previous post?
Kind Regards
Greg

[P3 Stoaker]

G'day All,
David and Mark, many thanks for the feedback.
David, if I may, I'm interested in a little more info on firing the oven insulated as I'm not really grasping the point. Whether insulated or not the firing and heating initially from within the dome through to the outside would surely be the same with or without insulation, after all the bricks will be the same temp throughout when starting the fire?? What am I missing here? Also, how would one know the extent or degree of cracking if the dome is covered?
Mark, cracking as shown in photo's. No detectable heat rise using a heat gun near the cracks suggesting no hot air is escaping, and the last fire was real hot. I do have 2 minor cracks through the inner arch along joints at the top, not shown in photo's, very minor.
Thanks again, it's all great info.
Kind Regards
Greg

[MarkJerling]

G'day Mark,
I ended up doing an even bigger and hotter fire today. A little more cracking but I'm fairly sure still what would be considered minor in respect to the thickness however there are quite a few.
I'll probably grind out a little and refill, then into the insulation. I didn't lay my brick base. Its fairly big and not really straight forward and I've not laid bricks before so I got a brickie to do it, and I'm glad I did. Pics posted on the first page or 2
Kind Regards
Greg

Please post some photos of your latest cracks. Are these inside or outside the oven? I've read the advice here that it's a good idea to insulate prior to first fires.

I did not realise you did not build your brick base. I've never laid a brick before but after building my base I was an OK brickie by the time I got to the dome! LOL

[david s]

Greg, if you have been firing the oven uninsulated then it’s probably the reason you’ve got cracking issues. Heating one side of the dome whilst the outer surface is cool, sets up uneven expansion stresses. If it’s insulated the bricks have a chance to be more evenly heated resulting in less extreme temp and expansion difference. You aren’t the first to experience this and there’s not much you can do to fix it. You can try grinding out the cracks and refilling them, but the cracks are still there. The oven can’t collapse and should be fine.

[P3 Stoaker]

G'day Mark,
I ended up doing an even bigger and hotter fire today. A little more cracking but I'm fairly sure still what would be considered minor in respect to the thickness however there are quite a few.
I'll probably grind out a little and refill, then into the insulation. I didn't lay my brick base. Its fairly big and not really straight forward and I've not laid bricks before so I got a brickie to do it, and I'm glad I did. Pics posted on the first page or 2
Kind Regards
Greg

[MarkJerling]

Those look like relatively minor cracks. Trick would be to see if they get worse or if that's it! Always nice to make the first pizza! I see you built a brick base. (As did I) Nicely done!

I had three or four small cracks in my oven and they did not get any worse. I've not filled them with anything as I don't imagine it matters.

[P3 Stoaker]

G'day All,
Exciting times, I've run a series of curing fires over the last 7 nights, starting very small with a little charcoal and gradually getting bigger. Last night and this evening I thought might as well cook pizza as the fires are getting hot. I've been using a heat gun and whilst I have increased the temps I think another good indication is the size of the fire and amount of flame. I thought I had a fairly hot oven tonight but the pizza's were taking 5-10 mins to cook so I think that isn't all that hot. Mistakes and tips;
1. I've made some plywood boards, I make the pizza on the board and slide off onto oven floor, works a treat. I did read a tip suggesting that just before actually topping the pizza turn the base over and the drier dough that was on top allows easier sliding off for the pizza, this definitely works.
2. I cooked tonight just after moving the fire to the side from the centre. Not a good idea, the floor of the oven was way too hot where the fire had been.
3. And the pizza, terrific, awesome.

I do have some cracking around the dome, as seen in the photo's. The cracks appear to open up when the oven is hot, not surprising. I cannot detect an increase in heat at the crack compared to either side when using the heat gun indicating air is not getting through from within the dome. Questions
1. Will the dome cracking open and close during each heat cycle over the life of the oven?
2. Any thoughts/recommendations as to whether the cracks should be repaired at all and if so whats the best way? There is quite a few, some possibly slightly wider, I'll grind out the mortar if recommended but certainly not unless it's beneficial? I do expect the cracks would be considered minor.
Many thanks and kind regards

[P3 Stoaker]

G'day Barry,
Many thanks for your comments. I've quite enjoyed design and build of the entry, much more than the dome. The cutting was really quite straight forward and I did what I could on the petrol saw but its quite old, vibrates a lot, moving the work and the table isn't all that accurate, but it worked well as a bit here and there doesn't matter. I also cut a lot freehand and dry with a 5 inch.
The grooves are as you say, my attempt to get things to hold together a little better. I figure even if the hairline cracks appear, as expected, the grooves might help to keep it all in place. I figured probably couldn't hurt ??
Please keep in touch and sing out with any questions.
Kind regards
Greg

[Baza]

WOW - a guy takes a hiatus from the forum and comes back to AMAZING work!! Greg - you're work is EXQUISITE!!! The cuts, the build, the thinking - and THANK YOU for sharing the pics and questions - you are helping us all so much. Grateful for your build questions here - when we get out of the winter and I'm back to building - I will be at the vent arch stage and this work here will help immensely!!

Wondering about the notches you cut in the brick? Is it to provide more hold when mortaring?
As for firing - I've seen many schools of thought - blanket and burn and others being burn - then blanket - then finish burn (as you suggest).
Given the purpose is to cure and release moisture as well - I think your approach will work ... and like your build and Russell's advice to EVERYONE that starts their cures: GO SLOW! Small fires, slow and steady over time.

Honestly - Happy for you mate! Great stuff!
YOU GOT THIS!!!

Barry

[P3 Stoaker]

G'day All,
Well the time is near and I've read up on curing fires. I plan to run the series from around 100 deg f through to about 700 deg f from memory before I insulate the dome. That will allow me to see the cracking and address/repair area's if needed. I'll then run a few more fires and eventually insulate, 2 inch blanket and 2 inch perlite.
One question for the wisdom of the forum, I read conflicting approaches to the duration of each fire. Some say get to the target temp and let it burn out/cool, whereas others say to keep that target temp for a while, presumably a few hours if possible.
Interested in your thoughts/recommendations.
Kind Regards
Greg

[P3 Stoaker]

I benefited greatly from photo's, here is a few more of the vent.

[P3 Stoaker]

G'day All,
Previous post questioned typical render thickness. I ended up going with about 10mm (1/2 in) for the top layer of the vent, photo no 1.
Not sure if it was a huge overkill but I wanted the vent brickwork to transition from the rectangle, in the actual arch to round by the top of the vent brickwork. I will be covering the top with a stainless plate, sides turned down around the edge and a riser welded to the plate that the flue can sit over. The oven is outside so any water running down the flue will be directed away and not end up on the vent floor. The relatively smooth transition from rectangle to round should encourage the exhaust UP, with any luck. I wasn't sure if the top stainless plate was over a larger rectangle with an 8 inch exhaust hole in the middle, if the exhaust would cavitate or circulate and resist heading where I want it to?
Thanks again for all the assistance and idea's, lots of those in place as seen below.
Kind Regards
Greg