#11  
Old 05-11-2009, 04:07 PM
Peasant
 
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Default Re: Dave's cast refractory oven

Back to the story. Time to start tidying things up. Pointing the front arch makes all the difference in the world to how finished it looks. I did it at the end of a long session of making not much progress on something or other, and it cheered me up no end.

Slate tiles on the stand around the dome. The dome and stand will be painted creamy-ish. (Actually the dome got a first coat 3 hours ago. But I haven't got any pictures - too dark ;-). Stainless twin-walled chimney - just balanced in place here.
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  #12  
Old 05-11-2009, 04:17 PM
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Default Re: Dave's cast refractory oven

Which brings me back to FOOD!

Pizza last Sat, roast dinner (breast of lamb rolled up with herbs and a little lemon juice, roast potatoes) on Sun. No pics of the lamb :-( but a few of the pizza - with a happy man!

For the pizza I was too timid with the fire - both for the initial firing, and in the size of the fire I kept going while cooking - so it took a few minutes to cook, but still tasted fantastic!! Plenty of learning to do there. My dad always taught me when building and managing wood fires that "you're trying to heat the room, not burn wood" so my normal wood fires have lots of glowy embers - I think I need to relearn that for the oven, and start "burning wood" with sky-high flames. But it'll be fun to practice!

Huge thanks to James for the plans (even though I didn't follow them much they provided vital inspiration) and running the forum, and to aureole with a very kind donation of materials which really kick-started me into action. And to all on the forum for inspiration - and pictures of ovens to aspire to / fail to live up to!
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  #13  
Old 05-11-2009, 05:20 PM
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Default Re: Dave's cast refractory oven

Quote:
Originally Posted by David Reekie View Post
Les - yes I am, and no they are not. I have my fingers firmly crossed !

Seriously, they ought to be OK for chimneys, which is basically what this is. I hope.

I'll report back if they fail :-(

David - it gets pretty damn hot there. I thought the general consensus was there may be an expansion problem between the cores and the mortar inside the core holes. Definitely keep us posted as this will further the knowledge base.

Les...
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Old 05-12-2009, 01:08 AM
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Default Re: Dave's cast refractory oven

What a cool oven! And I love the setting and all those tille stone walls in your garden. Thank you for posting that, I enjoyed reading about your build.

Please do let us know how things progress - it'll still take a while before your oven is fully cured (specially with dinky little fires like the one in the picture ). Not that I would expect any problems, it all looks very well thought out and beautifully built. As for the bricks, we will see... If its anything to go by, I didn't use refactory bricks for my outer arch either, but it was all a bit different anyway.
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Old 05-12-2009, 01:29 AM
Peasant
 
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Default Re: Dave's cast refractory oven

Thanks Frances - it was fun writing it up too, as well as building it.

Re the bricks - and answering Les aswell - different expansion between the concrete in the cores and the bricks is a good issue - I didn't think about that one. I might get away with it - the bricks with the filled cores are at the sides of the arch, the top bricks are cut away to provide the vent, and they are the only ones which have got really hot so far. We shall see...

Frances - you're right that it isn't cured yet. I made a stupid mistake at one point and got the insulating slab under the oven a bit wet, and it definitely isn't dried out yet - the concrete slabs get far too warm far too quickly, and the oven doesn't retain heat well at all. Hopefully nothing a few more fires won't solve. I did wonder at one point about building a big fire under the slab in the wood store to help dry it quicker, but have resisted so far
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Old 05-12-2009, 02:25 AM
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Default Re: Dave's cast refractory oven

Good work David! Nice to see most o the bits have been used up, at any rate. You worked quickly once you got going, too.

I found the castable refractory stuff cured a lot quicker than regular cement, so hopefully it won't be a bit issue for you. There's always the option of coating the inside with something else if you want to reflect the heat back (like the original romans used the Pozzolana).
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Old 05-27-2009, 07:22 AM
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Default Re: Dave's cast refractory oven

Dave,

My discovery of your post is so timely.

I've been wrestling with the idea of doing a cast in place oven for some time.

I always get overwhelmed with designing the mold. Do I gather that you simply made the interior mold and then plastered the outside of it with refractory concrete.....no female form for the outside?

I also note that you did it as a single unit. Any expansion and contraction problems anticipated?

Thanks very much!
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Old 05-28-2009, 08:58 AM
Peasant
 
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Default Re: Dave's cast refractory oven

Good questions.

As you say, I built it over dome of earth/clay, well patted down and covered with strips of old newspaper. I plastered it on with a plastering float. I had no external former. This worked really really well for me - the correct consistency of the refractory concrete I used was much drier / stiffer than normal concrete, and I was able to built up the full thickness in two coats quickly applied without the first one drying, with no slumping at the bottom of the sides. I was amazed at how easily this part of the project went - I was dreading it a bit, but the concrete made it very very easy.

I've now had the oven right up to temperature with some properly big fires - over 500C (about 950F) dome temperature. So far cracking has been minimal - I have not seen any cracks to the dome at all, and there is just one crack in the floor. This is better than I expected!

I am still a bit cautious about how fast I heat it up - it's taken me maybe 90 mins to build the heat, and I could have built a bigger fire more quickly. Maybe I'll have problems if I do that, I don't know yet.

It stays hot while cooking very well - I had no problems cooking pizzas for about an hour for a big party - did 20+ pizzas, mostly taking around 2 mins. It ws slower to make the pizzas than to cook them.

I still don't know how well it will ultimately retain heat after the fire goes out - I'm definitely still drying out the insulation under the oven, so it cools down quicker than it will when that insulation is dry. I don't expect it to ever be as good as a thicker brick oven here - but I expect it will get up to temperature quicker. A thicker cast refractory dome would be slower to heat up but stay hot longer.

So at the moment, I'm very pleased with performance and don't have any real problems to report. Even the brick entry arch / chimney support is holding up fine so far.

I'll keep reporting back if I do hit any problems.


dave.

ps - I've now done fillet steak as well as pizza - came out great!!!

pps - I have no evidence for this, but I bet that refractory concrete is much more variable than firebricks. So the stuff I got from my supplier might be very different to what you get. That might be your biggest risk. I'm not sure I can help you much with this issue - I used 'Pencrete 1300' but haven't found any proper spec sheets for it.
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Old 05-28-2009, 09:53 AM
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Default Re: Dave's cast refractory oven

Thanks very much Dave! Its a beautiful oven.

I'm thinking that I will use a very simple former for the first 5 or 6 inches and free float from there.

Perhaps I will also cast in a very thin (1/16") section of wood dividing the quadrants into quarters. Once the wood burns out I can seal with morter and have an expansion joint.
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  #20  
Old 05-28-2009, 11:17 AM
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Default Re: Dave's cast refractory oven

Quote:
Perhaps I will also cast in a very thin (1/16") section of wood dividing the quadrants into quarters. Once the wood burns out I can seal with morter and have an expansion joint
I'm not sure an expansion joint is what you want here. It sounds like a smoke leak opportunity to me. If you want to segment your dome as an anti-crack measure I'd use something thin and non combustible like foil or a special refractory paper that's used for this purpose
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