My latest precast oven, struck today

[david s]

Hi, I have just returned after many years , also have pulled the mold out of a friend's garage, I'd like to cast again but the refractory concrete is just a crazy price now, does anyone have a recipe for diy refractory concrete that will hold heat?
thank you from the UK

Check out the homebrew cast ovens in the "other ovens" section. The recipe is 3:1:1:1 with the addition of burnout fibres to reduce the possibility of steam spalling and perhaps fibres for strengthening.

[sonomacast]

Hi Sonomocast,

Is it possible to share the detailed moulding process?

Thank you.
kingandenzo

Hi, I have just returned after many years , also have pulled the mold out of a friend's garage, I'd like to cast again but the refractory concrete is just a crazy price now, does anyone have a recipe for diy refractory concrete that will hold heat?
thank you from the UK

[UtahBeehiver]

King,

This is a really old post your are asking your question. Very much doubt the poster is active any more.

[kingandenzo]

Hi Sonomocast,

Is it possible to share the detailed moulding process?

Thank you.
kingandenzo

[casper]

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

[Tiggi]

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

[david s]

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.

[casper]

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)

[david s]

Re: My latest precast oven, struck today

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

[casper]

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?

[david s]

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

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.

[casper]

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

[chale]

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?

[sonomacast]

Re: My latest precast oven, struck today

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

[Tiggi]

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?