42" Pompeii construction in Adelaide

[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

[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 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

[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.

[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

[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

[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

[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. 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.

[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

[david s]

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.

I don't think it really matters where the vent is, because it's a bit like the hole in a saucepan lid just to relieve pressure, but make sure wasps and other insects can't make nests in it and block it up and make sure water won't run in. Steam pressure is more likely to build up at the top of the dome where it'll be hotter so you could make a case for placing a vent at the base of the dome where the steam pressure will force water out. When firing a new kiln for the first time, empty and to service temperature typically water will start dripping out from at least one bottom corner at around 400 C. so perhaps that's where its drain should be.

Regarding the dome to hearth joint I use Flexible Pointing to seal up the whole dome and make sure there's a pretty thick coating at that joint. If you water down the stuff 20% you can simply paint it on.

[MarkJerling]

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

Sorry for the late reply. That does look like very minor cracking to me. I would not worry about it.

[P3 Stoaker]

G'day David S and Mark,
Thanks for the reply and info. I think I'll put the vent towards the back, probably half way down?? I'm not really sure yet.
I found a business here in Adelaide called Construction Chemicals. They are most helpful on the technical advice side and their products are more than meeting my needs, or will I believe, yet to use many.
When I asked about a render I wanted water proof and was planning on adding fibres. They sell a render covering these requirements, waterproof and fibres already added. I'm yet to use it but seems like it should do the trick.
Question for any Aussies, what vent did you use? I have seen plenty of pictures from Russell and others but I'm not having much luck here in Aus. Has anyone purchased one? Do you know the name of the item?
Kind Regards
Greg

[MarkJerling]

Try these guys: Xylem Australia 2 Capicure Drive, Eastern Creek, NSW 2766

[P3 Stoaker]

G'day All,
Thanks for the info Mark. I ended up cornering myself in that I'd never found a vent, despite searching and the weekend was here, insulation and vermiculite. I needed a vent fast and made one. Hope it will be alright but seems fairly simple, let pressure out !!! I just plugged the elbow but I drilled a couple holes in the cap. I jammed steel wool in both ends. Ref photo 5.
I had a gap to fill, photo 6. The floor bricks are on calsil board (cannot see). The grey strip is concrete foam and the white bit is vermiculite. So filled the gap with v-lite.
I ended up using wire running across the dome to hold the blanket in place. I anchored wire loops at the bottom, photo 4. Worked well.
Started the v-lite yesterday as recommended and that provided a firm footing to continue this morning.
Todays photo's in the next post.
Regards