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Record of my 32" Homebrew cast oven, on a brick base - West Midlands, UK

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  • It looked ok. There is an overriding principle with casting and that is to provide a release. This means instead of having straight sides the mould form should be made so there is a slight angle, maybe only one degree. An example of this is a bucket with a slight conical form. Of course a sand mould doesn’t need this requirement because the sand can be easily removed. Polystyrene is also easily removed. Providing a release from the mould form is actually more important than the application of a release agent like oil.

    There’s nothing worse than not being able to separate the casting from the mould.
    Last edited by david s; 08-05-2020, 06:06 PM.
    Kindled with zeal and fired with passion.

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    • I learned that. The mold was made of polystyrene but I had to use a forstner bit to drill it out. Good thing it was polystyrene.

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      • Nick J C quick question - once you had finished the final render cost and removed the card around the flue - you must have had a ~5mm gap - what have you done about that? Some sort of sealant? I know your oven is covered (and I plan for mine to be too) but I assume we still need to prevent moisture getting in that gap?
        My cast oven build thread

        https://community.fornobravo.com/for...-castable-dome

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        • Silicone. I used high temp silicone as I happened to have some , but standard stuff takes fairly high temperature . Both will melt if you allow flames into the flue, but should be fine if you are careful. My flue gets to around 150c at the point of exit, although bear in mind it has a fairly tall outlet

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          • Slowly progressing on roof, as real work and children demands..... decided to try to tile up close to the flue, and probably silicone it in to finish, rather than flash it in lead but will see how it looks when it is all bedded in
            Last edited by Nick J C; 08-18-2020, 10:50 AM.

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            • Laying ridge tiles

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              • Nick J C Hi and I hope you're well! I am just about to have a go at a door and I wondered if you could help m with a few questions please? I am hoping to make something like your's, as it looks effective and hopefully, fairly simple.

                Did you leave a small gap for expansion? I wondered which, between the door and the oven expanded and therefore, if a gap is even necessary.
                How has the design held out? - anything you would change?
                What mix ratio did you use for the V.Crete and did you reinforce it?

                Thanks again for all the previous help and in advance, if you get a chance to answer some of the above.

                Although I am still looking back, thinking I could have made a better job of certain elements, I am really happy with the oven overall and honestly, your build thread has been instrumental in getting me over the live, so cheers!

                Tony.

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                • Hi TonyPizza. Pretty happy with my door, although I am sure it won't last forever. I used cement board cut to about 5mm smaller than the opening all around, which sits against the flange, with glass fibre stove rope all around to make a reasonable seal. I put some aluminium channel on the edge to stop it chipping. The vermicrete is a reasonably rich mix of about 5:1, so insulation value sacrificed for strength, but still only warm to touch. The vermicrete layer is just smaller than the hole, and glued to the cement board with flue cement.
                  Last edited by Nick J C; 09-26-2020, 06:44 AM.

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                    • Nick J C Outstanding build and very informative thread, I'm about to start my second build, the first was a cob/clay dome hybrid with ceramic insulation, and you have given me lots of points to work on!
                      I'm intrigued to know how much better the Homebrew domes work...what are your heat up and cool down times like? how does it hold the heat over 24hrs say.

                      Lots of West Mids builders on here.....maybe we should have a West Mids thread?!

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                      • Aloha Nick and thanks for the share... awesome job on the oven... I’ll be building mine soon in a very similar fashion.. I have learned something very important from this thread that I will need to consider for my build... I live in Hawaii.... in Haleiwa we get about 39 inches of rain a year... I was under the impression that after everything you do a final render with a water proof stucco to make it water proof and then seal that... but as David s and russel have mentioned completely water proofing/sealing the oven does not allow it to breath or release steam..??? Thus cracking?

                        I also noticed your copper pipe vent at the top of your dome that goes to the insulation blanket... this allows moisture built up in the oven to escape?? I would be afraid to install something like this in Hawaii as I would fear it would allow moisture into the dome...

                        so after much reading and studying and learning I still don’t have a clue.. and I’ll be going to sleep wondering.... I always thought you waterproofed and sealed these at the end... and if you don’t how you keep water out of them..?? and I can’t afford to build a whole structure over the oven.... my wife is telling me maybe we should just get an off grid propane oven... it certainly would be easier... I guess I am a sucker for the hard way... uhhhggfg.... thanks again for everyone’s help and advice...
                        My build:: https://community.fornobravo.com/for...nch-wfo-hawaii

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                        • Originally posted by Dan350 View Post
                          Nick J C Outstanding build and very informative thread, I'm about to start my second build, the first was a cob/clay dome hybrid with ceramic insulation, and you have given me lots of points to work on!
                          I'm intrigued to know how much better the Homebrew domes work...what are your heat up and cool down times like? how does it hold the heat over 24hrs say.

                          Lots of West Mids builders on here.....maybe we should have a West Mids thread?!
                          Hi Dan350 ..... My oven heats up to a clear dome inside in between 1 and 2 hours depending on how carefully I attend it. When I am done with it for open fire/pizza cooking, when the fire has gone out, I close off the door, and it is usually still hot enough to cook bread by the following morning (200 C). Heat retention with a well insulated dome like mine is pretty much determined by the door design I would have thought. Mine is average in terms of insulating capacity but was quick and easy to make. A door with a thick cavity stuffed with ceramic, and well sealed with glass rope im sure would make it better performing.... Sure are lots of Brits in the area on this forum.... lots of time at home I guess...Now Ive had the Covid vaccine im feeling brighter about the future!

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                          • Originally posted by Boogie-D View Post
                            Aloha Nick and thanks for the share... awesome job on the oven... I’ll be building mine soon in a very similar fashion.. I have learned something very important from this thread that I will need to consider for my build... I live in Hawaii.... in Haleiwa we get about 39 inches of rain a year... I was under the impression that after everything you do a final render with a water proof stucco to make it water proof and then seal that... but as David s and russel have mentioned completely water proofing/sealing the oven does not allow it to breath or release steam..??? Thus cracking?

                            I also noticed your copper pipe vent at the top of your dome that goes to the insulation blanket... this allows moisture built up in the oven to escape?? I would be afraid to install something like this in Hawaii as I would fear it would allow moisture into the dome...

                            so after much reading and studying and learning I still don’t have a clue.. and I’ll be going to sleep wondering.... I always thought you waterproofed and sealed these at the end... and if you don’t how you keep water out of them..?? and I can’t afford to build a whole structure over the oven.... my wife is telling me maybe we should just get an off grid propane oven... it certainly would be easier... I guess I am a sucker for the hard way... uhhhggfg.... thanks again for everyone’s help and advice...
                            Hi Boogie-D ... Good luck on your build. My advice is that you cannot rely on the dome itself to remain waterproof without protecting it over and above 'waterproof stucco' or paint etc over the final render coat. Unless you have very infrequent rainy days (unlike UK) you will be spending quite a long time 're-curing' your oven after a wet spell/at the beginning of the season... basically you will have to wait a long time to reach temperature, and have a smokey time of it, for a few times before your oven is dry again. Even if your oven is covered, there will be slow moisture ingress over the weeks, and this is why a hole is designed into most ovens to allow this to pass out as steam/water vapour without pressurising the shell and cracking it. Mine was a very straight forward affair (I have posted how I made it) although I did get my son to 3d print me a cap - it could be done pretty easily with a dome of copper/plastic resting on the top.

                            On balance, I do not regret building a roof for my oven - I havent bothered to even paint it yet, and may not, as I quite like the concrete colour, and it allows it to 'breathe' a bit. My roof was an extravagant affair with tiles I reclaimed from our house, but that was just because I wanted to spend time on it as a recreation - and there was no rush to build it, as the oven was working perfectly by then and the pressure to see the first pizza was nolonger on. For most of the time, I just had a plastic canopy over it, and that worked perfectly well, but just wasnt pretty.

                            Your other option would be to enclose the whole oven in its own house - although conceptionally this sounds like more work, I dont think it is, because you dont have to render the oven shell, and dont need to be so careful about the construciton aesthetics, and creating a perfect hemisphere. You can also shove in as much cheap insulation as you like in the space between the housing and the homebrew cast. On balance, I am happy with what I did, but mainly because I was most interested in developing the skills of construction and the oven appearance, rather than the pizza quality.

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                            • Thanks... a lot to think about.... luckily I live in a pretty dry area of the islands (39 inches a year) summers are like a desert... and I could cover with a tarp... right now I am very uncertain if I will begin building my oven at all... fire bricks... I’ll explain on my build thread..
                              My build:: https://community.fornobravo.com/for...nch-wfo-hawaii

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                              • Originally posted by Nick J C View Post

                                Hi Dan350 ..... My oven heats up to a clear dome inside in between 1 and 2 hours depending on how carefully I attend it. When I am done with it for open fire/pizza cooking, when the fire has gone out, I close off the door, and it is usually still hot enough to cook bread by the following morning (200 C). Heat retention with a well insulated dome like mine is pretty much determined by the door design I would have thought. Mine is average in terms of insulating capacity but was quick and easy to make. A door with a thick cavity stuffed with ceramic, and well sealed with glass rope im sure would make it better performing.... Sure are lots of Brits in the area on this forum.... lots of time at home I guess...Now Ive had the Covid vaccine im feeling brighter about the future!
                                That's good news! (About the vaccine) I didn't think anyone much under 60 was getting it anytime soon?!

                                So as I was prob at 100c the day after doing pizza, but my door was only 1/2" wood with big gaps around it and sat in front on the flue - a very poor design, I've just rebuilt the gallery using your pictures for guidance and got a mate doing me a steel door on the plasma Jig at work! Hopefully be more like 200 the next day then and better for slow cooking!

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