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  • david s
    replied
    A 5:1 vermicrete is not a dense refractory layer so will do virtually nothing in regards to contributing to thermal mass. As it is an insulating mix it will be resistant to absorbing heat as well as being unable to store it. If you look at the table I left in my last post you will see that a 5:1 vermicrete has very low strength (around 200 psi compared to a proprietary castable refractory of around 4-5000 psi see CCS cold crushing strength for the product I use, on attachment). Stainless needles will do little to strengthen such a weak mix. Other builders have replicated the gym ball/ vermicrete domes, but none have offered performance in the long term, even after invitations to do so. i suspect they all fail due to the poor strength of the inner dome which apart from thermal expansion tensions, is subject to knocks and abrasions. Do plenty of research before proceeding, or build a real cheapie with the intention of a rebuild once you learn its deficiencies. Suggest you start searching this site for mobile ovens and also look at home-brew castable. As you're in the UK also try their forum ukwoodfiredovenforum.

    TDS - CASTFLO AG 1450 ARG.pdf
    Attached Files
    Last edited by david s; 08-06-2019, 03:25 AM.

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  • badrobot
    replied

    I should probably stay realistic on what I need to achieve here which is to establish a mobile wfo, (it may be that just buying one in might be the better option at the beginning)

    That said I would still appreciate any advice, guidance on a developing a sound method as I will still explore my own build using a castable I make myself. 1 part refractory cement/5part vermiculite+SS Needles (which I am yet to purchase) I may forgoe the cut brick idea at this stage until I have the time/funds, it was just a thought. Definitetly something to experiment on at some stage. Do you think it is possible to find a proprietary castable refractory cement/brick combo that might work together?

    The working space/ internal trailer sizes are: L1400xW900xH500 the top half of the trailer.


    So to summarise, I figure the oven being around approx 850mm external at the base with a max height of 420mm, allowing space for plinth, with room for an arched entrance depth of around max 400mm.
    the main dome of 60mm thickness, consisting:
    1 part refractory cement
    5 parts vermiculite
    2-5% SS needles to add strength
    ceramic fibre layer of 1-2inch
    all tied in with wire/chicken wire
    a scratch coat, to give final layer a key
    then a final layer of render (not quite sure of most appropriate thickness of render for this build?) or what to best make this layer out of?

    Do you think I am on the right lines?

    This is an example:

    This oven has the attention of detail I liked and would love to recreate (great open flue design/heat retention/herringbone brickfloor/build quality) sadly the spec/cost are too big for my requirements alongside shipping costs from states/australia.

    https://www.melbournefirebricks.com....ired-oven-kits

    I am totally willing to be educated/pointed to other places to swat up further. Do you know of a good reference point regards making a 'small' mobile oven. I had put those figures 10-25mm and 50-60mm as a guide initially as I was not set on sizes.

    Hope this all makes sense. Thanks David


    Last edited by badrobot; 08-05-2019, 04:18 PM.

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  • david s
    replied
    Click image for larger version  Name:	image_83170.jpg Views:	1 Size:	332.7 KB ID:	415700 Iím unsure of the finer detail of what you are planning. ď 10-25 mm firebricksĒ does that mean some are 10 and some are 25? and 50 mm inner dome thickness or 60 mm? You canít be sure about the thermal expansion of the firebricks and your castable mix at different temperatures which could be problematic. What kind of castable are you considering? Will it be a proprietary castable refractory or refractory cement with added aggregate? Melt extract fibres are the recommended reinforcing for castable refractory and will increase strength if added a min of 2% by weight of dry castable. If you go above 5% it makes the mix less workable and as theyíre called needles so you need to learn to handle them carefully.

    "the shop bought ones are only pre cast in parts also" That is true and apart from making handling the pieces easier, making assembly easier it also provides for thermal expansion. It's also true that some manufacturers provide a one piece dome for mobile use as it's less likely to rattle to bits.

    Adding sand to an insulation mix will add needless weight and drastically reduce its insulation value (see table attached).
    Re moving the dome, you need to do a calculation to work out itís weight. You donít say the ovenís size, but a small increase in diameter produces a big increase in volume and weight.

    The beauty of the sand mould is that you can cast the dome on top of the floor right where itís going to be, no moving.

    Concerning catenary arches, of which I am a big fan, unfortunately although their stability is superior to any other arch, to get one low enough for a pizza oven, produces unusable space at the floor level because of the walls being at a lower angle in that area.
    The hemisphere, as 2000 years of Roman ingenuity has proved, is a far more suitable form.



    Last edited by david s; 08-06-2019, 03:10 AM.

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  • badrobot
    replied
    Originally posted by david s View Post
    I think you might be headed for trouble.
    If itís a trailerable project then any oven brick or cast is subject to bumps and vibrations that heavy brittle material does not like. An all brick oven is likely to rattle to bits. Some manufacturers offer a one piece rather than multi sections for trailerable ovens for this reason. Generally a 50 mm casting, well insulated is quite sufficient thermal mass. Whereas a 50 mm thick brick dome has insufficient thickness for the bonding of the bricks, stationary or mobile. Iíd be concerned that a marriage between thin bricks and casting, whilst probably ok for a stationary oven, would have too much inherent structural weakness for longevity. But Iíd love to see you try it and report back.
    Regarding the gym ball idea, because it requires a fair amount of formwork and necessitates removal, lifting and replacement of the heavy cast dome, it will be way more trouble than using the sand mould method where the dome can be cast in situ.
    Hi Dave , Thank you for your feedback. Trouble ya say....

    The casting of my own only intends to replicate the likes of which can be standard fare for any mobile set up really, 50mm for inner part -50mm for the insulating outer seems a reliable and an appropriate one in my case regards weight/mobility. And the shop bought ones are only pre cast in parts also btw.

    I had planned to create a inner casing dome using refractory cement around 50mm thick + maybe melt extract fibers? I read on hear that you might be the person to ask about the latter. (60mm with said brick lining) and once cured another 50-60mm layer of sand/cement/vermiculite + something akin to straw to bind mix as the insulating layer to finish. Maybe then some sort of tiles if I can afford the xtra weight.

    In response to the gym ball method, I am a carpenter so a bit of form work is no problem, and there is no need to lift, remove cast dome as you can just pull the nozzle out of ball to deflate once its at least half way to curing (around a couple of weeks) once it cures it doesnt seem to be an issue, and I can always get some help to manouvre. I am thinking placing all cut brick lining on gym ball then carefully building up cement from bottom. I also figure their should also be some intrinsic strength gained from the regulated shape of the hard round gym ball not disimilar to the residual strength of a well built (arch) seen in Pompeii brick ovens, Something inherant in a catanery arch which is partly why I chose it over the sand dome method, but I totally share a concern regards the possible vibration from trailer. (as I understand melt extract fibers help with thermal shock but will they add strength you think? I am no engineer :/


    Last edited by badrobot; 08-04-2019, 02:30 PM.

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  • david s
    replied
    I think you might be headed for trouble.
    If itís a trailerable project then any oven brick or cast is subject to bumps and vibrations that heavy brittle material does not like. An all brick oven is likely to rattle to bits. Some manufacturers offer a one piece rather than multi sections for trailerable ovens for this reason. Generally a 50 mm casting, well insulated is quite sufficient thermal mass. Whereas a 50 mm thick brick dome has insufficient thickness for the bonding of the bricks, stationary or mobile. Iíd be concerned that a marriage between thin bricks and casting, whilst probably ok for a stationary oven, would have too much inherent structural weakness for longevity. But Iíd love to see you try it and report back.
    Regarding the gym ball idea, because it requires a fair amount of formwork and necessitates removal, lifting and replacement of the heavy cast dome, it will be way more trouble than using the sand mould method where the dome can be cast in situ.
    Last edited by david s; 08-03-2019, 06:44 PM.

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  • badrobot
    started a topic Mobile Community Oven Build In UK

    Mobile Community Oven Build In UK

    Hello all. I am looking for a bit of feedback around using/incorperating 10-25mm fire bricks (cut by me) to line the inside of a cast pizza oven self build. I am thinking of using the gym ball method.

    I have a pretty reasonable understanding of the way I need to go about it for the desired result, yet have this developing idea that I would really like to incorporate, so thought I would ask for some input.

    I would like to give the cast method some of the thermal mass qualities of the Brick oven method, though my project requires me to make it light yet robust (and costs to an absolute minimum) hence the gym ball/cast method, I already have most of the materials: including the ball, though I really would like to add the thermal mass and aesthetic quality of the inside of a brick oven to the project though with a total weight restriction of 650kg (Brenderup 1150s trailer) I can not afford the full weight of a full brick version but figure that in theory as long as the fire brick (tiles) are cut and packed neat and close together inc the keystone, the rest of the cast method should follow with no problem. Has anyone already done this? Any reason why it wouldn't work? Hope all this makes sense, does to me hah.

    Any relevant thoughts/questions welcomed.


    Many thanks
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