Adhoc 36" Oven in Lake District, UK

[SableSprings]

These new structures contain a lot of internal moisture. Remember that the oven expands as it's heated. When you put perlcrete/vermicrete directly on the dome, it will always crack simply because the oven expands and the "shell" doesn't expand as much. Most of us now recommend putting ceramic batting on the dome, do the curing and when the moisture is all driven off and out, the final hard shell is added. The fact that your blanket layers are hot is an indication that you are still driving off moisture from your build. Ceramic batting will also pick up moisture in humid/wet conditions just like the ceramic board. You just need to have patience and continue to fire the oven...it will gradually improve heat retention and reduce heating times as it becomes fully cured. Looking at your pictures in post #40, I'd assume the areas that are still black have not been fully cured. The top areas tend to cure more quickly than the lower levels (and cooking floor). A fully cured oven will start to clear at the top and move down the sides as everything comes up to > ~650F. If moisture is still in the mortar, bricks, or insulation that area will stay cooler until the moisture is fully removed.

It will be easier for the oven to cure without the vermicrete/perlcrete outer layer. Be patient and continue reasonable fires as long as things remain damp. A great tip from David S is to lay a piece of clear plastic over the oven and if moisture is still being driven out, it collects on the inside of the plastic and you know that you need to continue the curing process. The cooking floor is always the last to be cured with the moisture tending to be more "trapped" in the base insulation board and bricks...BE PATIENT!

Relax, you've done a good job and have a working oven...you are now into the finesse part ...enjoy an adult beverage with your items hot and tasty from the WFO.

[MickyPizza]

I crawled inside yesterday and brushed up the offending area. On quite close inspection and given the shee size of the external cracks, nothing to be worried about INSIDE. With the blanket lifted up to photo the cracks the other day there WAS steam coming up through out of them though. Maybe moisture from the external mortar joint and bearing in mind I'm hammer and chisel jobbing it - my mortar gaps are bigger than most folks on here...
I scraped the extrnal cracks out and smeared in some heat mortar to repair it. On inspection of my photos though, the second pic perhaps shows a crack my eyes never picked up on (top right)
Its nice to see my upper higgedly piggedly courses looking good to go though. Rained all yesterday so created a template for a door. Getting a local blacksmith to forge one for me. No rain today. Heat mortar to be plastered over the cracks today. Then will chicken wire the blanket in place for good!!

When I hit top temps, even with all them blanket layers on - it WAS quite warm on top so Im adding some, but not all, of blanket 2 on today.

Question.... (maybe for UtahBeehiver r SableSprings ) The blanket has been outside, covered by tarps etc. But - its damp. What do I do? Do I keep lighting fire after fire after fire, till it all dries out before adding the vermiculite/concrete layer. OR can I just light a fire, get the worst of the moisture out and continue on adding the insulating concrete without concern? Thanks guys..

[MickyPizza]

She's looking good... had to get MORE slate again. I got some kiln dried hardwood and managed to increase temps. But STILL not up to 700-800F . But you know what? I was just being impatient. !!! I rang my mate Tim who has a mobile oven and has now opened a Pizzeria in Inverness (Cheese & Tomatin) and he said (regarding the outdoor mobile one he has) It took 90 mins to 2 hrs to get to temperature!!!!! I kept adding more wood and mixing it with soft wood etc and temps went over 700F for the first time. Woop woop!!! But... I got impatient.....
I couldn't help but throw in my first pizza!! Took about 3 or 4 mins to cook...but it was a great moment.
In the end temps hit 811 F!!

And then.....the cracks appeared. Big dirty ones, all over the outside.

Some points...
I decided on leaving blanket loose for this reason, so I could check if any repair work was needed - it IS!!
When hitting temps of 500F or so, the blanket on outside was cool, but If I put my hand up her skirt so to speak, then the dome itself was quite warm. Which said two things - one, it works! And two - maybe I only needed the ONE roll of blanket on there (14.64M - 610 x 13mm (Density 96kg)

It was quite damp though even though it had been stored in the house.

[MickyPizza]

First chance to update. I have worked SOLIDLY for nigh on 6 weeks. Every single day (I have three jobs mind) and have went leaps and bounds in my progress.

I started on the slate entrance. I thought that if I tied in firebricks with slate rather than two seperate arches (one for front, one mini one for vent) then it would hold strength better. The Arch for vent was incredibly tricky and bricks seperated once. I mortared in some reinforcements to add more bind to them. I also used the time to light my drying out fires whilst working which served to help my new work set quite fast too
I really battered in that slate keystone until the whole arch felt like it wouldnt budge. Its weird working like this - it realy is a leap of faith that these arches wont collapse when you haven't done them before!

I created a facade (hollow) which, when the vermiculite concrete layer, then finally cement render goes on, you wont see the rear of it, just front and sides. I filled the hollow gaps in with vermiculite just for a bit of a laugh.

I got temps up to 500F or so. I stepped up slow, but these were only fires of max of 1-2 hrs. No door placed over or anything. I was really struggling to get over 500F... So I ended up with lots of regular 'medium fires'

Some cracks appeared but nothing major. Then I thought - because outside was drying nice, time for the blanket and maybe with THAT on, the extra insulation would increase internal dome temps...

[MickyPizza]

Looking good! Looks very similar to mine inside actually. Yeah I'm planning on covering it with a layer of ceramic blanket then vermicrete. You can't really see from my photo but there's a gap left in the top of the outer arch for the chimney. The front arch is deeper than it looks in the photo.

How are the fires working out? Any cracks?

Chris

Up to heat now Chris...mashooosive cracks on outside. But inside looks OK... read on....

[mazzazza]

Looking good! Looks very similar to mine inside actually. Yeah I'm planning on covering it with a layer of ceramic blanket then vermicrete. You can't really see from my photo but there's a gap left in the top of the outer arch for the chimney. The front arch is deeper than it looks in the photo.

How are the fires working out? Any cracks?

Chris

[MickyPizza]

FIRE!!! Got the first fire done - newspaper only.
I couldn't locate THIS post - https://community.fornobravo.com/for...33-oven-curing (have done now) so only took it to around 170F Was burning for around an hour with lots and lots of paper continuously burned through. Will do another today with a bit of kindling and aim for just over 200F (what it SHOULD have been yesterday) and aim for 300 tomorrow. EXCITING!!!

[MickyPizza]

Hi Micky, Sorry for late response - I don't get notifications from here and I'm only on every few days. Yeah that's true - and Thai curry paste is way better in a pestle and mortar.

I'm scared of even leaning on my dome - I'm sure it's fine but don't want to put it to the test!

Looks good Chris. Not entirely dissimilar to mine, but I bet your upper courses are far neater. You gonna cover it all with a layer of home brew to seal it all up? Cant see how you are gonna do a chimney mind. I lit my first fires yesterday

[mazzazza]

Hi Micky, Sorry for late response - I don't get notifications from here and I'm only on every few days. Yeah that's true - and Thai curry paste is way better in a pestle and mortar.

I'm scared of even leaning on my dome - I'm sure it's fine but don't want to put it to the test!

Ha ha - I didn't see it - in the past I used to try and blag that I knew what people were talking about when they mentioned football but I'll admit now I don't have a clue.

https://www.youtube.com/watch?v=ESVjzf4FzyU

[MickyPizza]

Hi Micky, hats off to you for doing all that with just a hammer and chisel! I'm in Newcastle, at about the same stage with my oven. Just finished the front arch and thinking about what to do for a chimney. I've been cutting my bricks with a hand angle grinder with a diamond blade. Works well but creates shit loads of dust.

Chris

Nice one Geordie. Photo? Way I was thinking was - they never used power tools 200 years ago. Similarly if I make a Thai green curry - I bash the hell out of the ingredients in a mortar and pestle as them little Thai old wifeys wont be using a Magimix in their humble shanty town dwelling. But as with BOTH situations, boy its hard work Ive made for myself!!!

I read somewhere that the crowning moment is STANDING on your completed dome, I dont actually trust mine structurally, bit like Martin Dubravka in goal for the Toon....what a sickener it was tonight

[mazzazza]

Hi Micky, hats off to you for doing all that with just a hammer and chisel! I'm in Newcastle, at about the same stage with my oven. Just finished the front arch and thinking about what to do for a chimney. I've been cutting my bricks with a hand angle grinder with a diamond blade. Works well but creates shit loads of dust.

Chris

[MickyPizza]

At last, the dome is a done deal!!! All sealed with a good 1cm of heat mortar all round the outside (home brew) and after initial heeby-jeebys of being cramped up in the oven space, I just got on with it, cleaned up the cracks, mortared a little and wiped it all down with a damp and dry cloth.
The upper 2 courses are very wobbly looking and not forming a perfect smooth dome but I hope it will be OK.
Also - its hard to tell from the pic but there is a recess to the left of the doorway, just the way my brickwork doesnt match. Swehould I fill this? Or just leave it as is?

Waiting a week now before curing fires, letting this thing air and dry as much as possible. For the entrance and vent, I have roughly a brick length from oven arch to front of plinth, so Im gonna have a slate arch at the front and visible and inbetween, firebricks. These will be half bricks, but interspersed with longer bits of slate so they kinda dovetail together sotospeak.

[MickyPizza]

MickyPizza,

She looks just fine to me. All of that is going to be covered up anyway. In the old world, bread ovens weren't built to emulate the Pantheon. They were built to perform as efficiently as possible. I'm betting that she will cook just fine and that the slate finish will be stunning. My hat is off to anyone who tackles and completes one of these with a brick set.

Thank Joe - reassuring encouragement. I'd spent night before last reading numerous crack related posts on here too. Ive dug mortar out and resealed as best I can. It will likely crack once more during the curing process anyways!

[Gulf]

MickyPizza,

She looks just fine to me. All of that is going to be covered up anyway. In the old world, bread ovens weren't built to emulate the Pantheon. They were built to perform as efficiently as possible. I'm betting that she will cook just fine and that the slate finish will be stunning. My hat is off to anyone who tackles and completes one of these with a brick set.

[MickyPizza]

Then - disaster struck. The half ok/half 'it will do' keystone, when hammered in, one of the last course bricks shattered and the top of it fell into the oven. So, I removed keystone and said brick and made two more bricks. It (the penultimate one) looked a good hammer, tight fit, leaving a good wedge on the final keystone.
Well didnt I hammer it home with wayyy too much force and bloody split the oven!!!! I almost cried. Cracks down two sides, including one of the arch bricks has totally seperated and is just kind of floating by 1 mm now!

I scraped out grout as much as I could and started pushing more stuff in. I crawled inside and scraped out the worst of the interior cracks and mortared that up.

Im HOPING that when I do my interior final grout, that I can seal the damn thing up. To finish, I added the final stone and plastered mortar all over the top and any offending cracked joints as best I could. Hardly the 'crowning glory moment' I had been anticipating. I now have the arduous and tricky, interior clean up ahead of me.

In other news - I got more lovely Honister slate to make the exterior arch and clad the done with when finished.