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My latest precast oven, struck today

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  • casper
    replied
    Re: My latest precast oven, struck today

    You would think. For my first oven I stopped counting at 8 bags ?14 each
    That gave me a 3" layer all round
    A 3" layer of blanket costs ?60 for the one roll, yet performs better than a 9" layer of vermicrete
    Also, with really good insulation, the oven gets hot so quickly, less than half an hour, gets up far hotter and retains cooking heat till the next day, even two days.

    My first vermicrete oven was over edge on brick with 2"concrete overlay (6" wall) and 6" perlite insulation. Took 90' to warm up, never got above 220 degC, you could feel the outer surface losing its chill and continue to pass heat till the oven cooled to 60deg within 24hrs. Next oven brick was on the flat (3" wall) with 3" ceramic blanket and 3" ceramic board under. Fires to 400degC+ within the hour and 24hrs later is still 170deg

    Yes it is worth it, and no its not significant price difference

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  • Tiggi
    replied
    Re: My latest precast oven, struck today

    From my own casting experience I can say this is a way to do it. The whole process was easy and smooth. I built it in 5 pieces in my garage. I worked on the oven while building the platform and the rest of the stuff.
    I ended up with 3" thick walls and the material that I've spent on the concrete was about the same if not cheaper I would need to spend on the bricks.
    As far as the usage I do not see any difference from what others with brick ovens have reported. I can bake in it next day without firing it again. Just this weekend my oven was 550F @ noon after I did pizza night before.

    If you need any more details just let me know.
    Thanks

    Leave a comment:


  • david s
    replied
    Re: My latest precast oven, struck today

    Vermicrete is cheaper and you can use normal cement with it ok. The problem is drying the stuff out.Not so easy if you live in a wet climate.

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  • casper
    replied
    Re: My latest precast oven, struck today

    I see. I must have a go then at casting. But I want a 1m dia floor. To make the segments my refectory supplier has a useful insulating sheet rather like soft cardboard, so a good way to keep the separation?

    Still, cutting a brick in half at an approximate angle is easy to do, makes the curve and joint thin enough. I used a 9" angle grinder freeform cut by eye, more or less at the right camber and angle of cut. Or the brick can be bought as an arch brick too, ready shaped to make a curving arch with the merest smear of cement.
    1m oven took about 70 bricks at ?2 each, and two buckets of wet cement at ?23 each

    Either way I would recommend using the ceramic blanket and the best heatproof board for under the floor, at least 3" all round. Makes a massive difference, I would never use vermiculite concrete again, nor insulating concrete which is just firecement with perlite mix)

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  • david s
    replied
    Re: My latest precast oven, struck today

    Creating compound curves with bricks is both difficult and time consuming.

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  • casper
    replied
    Re: My latest precast oven, struck today

    Good to know. I haven't tried castable, except to hang a cast hood smoke chamber to free up the stage from supporting the chimney and give me a clear platform. Yet I wonder why bother casting when it is easy to build with bricks?

    Leave a comment:


  • david s
    replied
    Re: My latest precast oven, struck today

    Originally posted by casper View Post
    FB and a raft of Italian and now British manufacturers are making segmented ovens, but that is for ease of manufacture in bulk. What would be your advantage?
    I have built two brick ovens now, the first a traditional barrel oven, then this Tuscan round one. Both are so easy, just a week for an amateur bricklayer like me

    1. castable oven materials is way more expensive than brick
    2. Far more complex for a one-off. Do it brick by brick and correct as you go, instead of remoulding and start again, complex moulds that take ages but are not re-used
    3. unless you have a vibrating table to compact the cement, its not possible to get strength unless you make it thick and heavy. Castable is not as strong nor as efficient as refectory brick
    Apart from creating more easily manageable pieces there is an advantage in having a number of sections because large cast refractory pieces tend to be more susceptible to cracking. This is the main reason floor bricks are laid loose and in smaller pieces.

    1. Yes, it is expensive stuff and because volume goes up cubed a small increase in diameter means a massive increase in material ($) So a cast oven is more suited to small ovens.
    2. For a one off you do not need a complex mould. A sand castle covered in wet newspaper to cast against by troweling the castable on is extremely fast. Yes you will probably get some cracks, but the spherical form means it holds together ok and the cracks don't get bigger.
    3.Using the method I described above and with careful placement of the castable and the addition of stainless steel needles, I believe that the castable is as strong and thermally conductive as firebrick.In fact in industry, here at least castable is being used increasingly as a replacement to firebrick.

    Leave a comment:


  • casper
    replied
    Re: My latest precast oven, struck today

    FB and a raft of Italian and now British manufacturers are making segmented ovens, but that is for ease of manufacture in bulk. What would be your advantage?
    I have built two brick ovens now, the first a traditional barrel oven, then this Tuscan round one. Both are so easy, just a week for an amateur bricklayer like me

    1. castable oven materials is way more expensive than brick
    2. Far more complex for a one-off. Do it brick by brick and correct as you go, instead of remoulding and start again, complex moulds that take ages but are not re-used
    3. unless you have a vibrating table to compact the cement, its not possible to get strength unless you make it thick and heavy. Castable is not as strong nor as efficient as refectory brick

    Leave a comment:


  • chale
    replied
    Re: My latest precast oven, struck today

    What did you use to divide the segment pieces? Also did you use an exterior mold or just pour to 3" over your current interior mold?

    Leave a comment:


  • sonomacast
    replied
    Re: My latest precast oven, struck today

    The dome used approx 400 kilos (880 lbs) of 1400 cast, Good luck

    Leave a comment:


  • Tiggi
    replied
    Re: My latest precast oven, struck today

    I am planing on casting an oven also, so how much of castable refractory did you end up using for dome itself?

    Leave a comment:


  • sonomacast
    replied
    Re: My latest precast oven, struck today

    Well I have just lost my Job, Construction is tight over here, So I guess it's back to Oven building

    Leave a comment:


  • casper
    replied
    Re: My latest precast oven, struck today

    I think James Bairey would be delighted. Its a passion for him that he wants others to share. Ever since he set this up he has offered encouragement to think we can do it too. Thats a big difference in attitude between entrepreneurs in California and here. Heck, he might even offer direct advice and support!

    Leave a comment:


  • david s
    replied
    Re: My latest precast oven, struck today

    Originally posted by casper View Post
    As far as i know fbuk dont manufacture anything. Not even for R & D. Should we stop making cars or boats because others do that better?
    Certainly not. But I think FB UK import from FB USA and then resell them. It is just that this forum is run by FB. Yes it's a free market and I believe there should be more local manufacture. The truth is that trying to compete these days with $1 per hour labour from Chinese manufactured goods is really hard. This includes FB manufactured ovens that use American labour.
    Last edited by david s; 04-29-2012, 02:00 AM.

    Leave a comment:


  • casper
    replied
    Re: My latest precast oven, struck today

    As far as i know fbuk dont manufacture anything. Not even for R & D. Should we stop making cars or boats because others do that better?

    Leave a comment:

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