Dave's cast refractory oven

[aureole]

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).

[TBM66]

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!

[David Reekie]

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.

[TBM66]

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.

[dmun]

Re: Dave's cast refractory oven

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

[TBM66]

Re: Dave's cast refractory oven

excellent idea!

Thanks

[mondo]

Re: Dave's cast refractory oven

TBM66 -

Regarding your 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..."

Are you thinking of creating the segments in the floor or in the dome?


Dave -

Outstanding project and I really think you're on to something. I find the prospect of constructing a full-fledged Pompeii oven daunting. I really just want something I can make decent wood-fired pizza in without spending a fortune. Pricing out a self-built Pompeii, I'm easily into $1,500 US and that's a lot to spend on something that will be used intermittently during the six or eight months of the year it's practical to cook outdoors around here. The ready-made FB ovens (excellent as they are) are up to nearly double that with shipping costs. I figure I can reasonably replicate your oven for under $500; maybe well under that.

Please keep us updated on how your oven ages, any structural problems that arise, etc. And thanks for a very creative contribution to the forum.

Mike Leary

[David Reekie]

Re: Dave's cast refractory oven

Thanks for the kind words Mike. I still love and am in awe of all the amazing brick ovens out there and want to build one someday when I have the space, but if my contribution helps someone else build an oven who would not otherwise have done I'll be very happy.

Funny you should ask for more updates on how it's doing. I took at good look at it yesterday evening, to check again for any more cracks. Previously I'd reported one in the floor, from one side of the entry arch to near the middle. That's not got any bigger. There is another one though that is either new or I'd missed before. It's on the top of the dome, from the middle of the entry arch back maybe 2/3 of the way up towards the top of the dome. Max width maybe 1.5mm or 1/16", at the arch. I don't think it's any kind of problem at the moment - as per previous comments, you could cast the dome in 2 or 4 pieces to start with deliberately and you'd end up with 'pre-existing' cracks like this. I'll continue to keep an eye on it and report back again if anything changes.

I'm very glad of the oven at the moment - we're having major surgery done on our house and have just had the kitchen ripped out, so last night's cooking in the oven (just sausages and roast vegetables) was out of necessity not choice. Still tasted good though!

[TBM66]

Re: Dave's cast refractory oven

Mondo,

I would use firebrick for the floor. I would envision using the paper refractory material that dmun suggested to create the expansion joints in the dome.

[MK1]

Re: Dave's cast refractory oven

I see where some of the masonry heater guys use a thin slice of the kaowool blanket where they need expansion joint filler.
Mark

[david s]

Re: Dave's cast refractory oven

An expansion joint can be easily made from a mix of vermiculite, sand ,lime and cement. It is pretty firm and has some (enough) elasticity.

[ChefDan]

Hi Dave, would it be OK to mix in small granular lava rock or another granular material to the refractory castable cement? Just trying to offset the costs of the refractory cement.

[david s]

Yes, but just be careful that you don't mix up too much at a time. Refractory (calcium aluminate) cement goes off way faster than Portland cement particularly if it's warm.

[ChefDan]

Thanks Dave. Would you recommend the portland / perlite homebrew instead of refractory castable?

[david s]

Yes, but if you have the castable already you could use it. I'd be seiving the course aggregate out of it first though. Most modular cast ovens butt the castings together and fill any gaps with refractory mortar from the outside. I do a stepped joint for mine but this is more difficult to organise in the mould, especially if you are doing a one off casting. An expansion joint is better placed in a position that will allow free movement of the inner oven and or the entry, against the cooler outer decorative arch and the outer shell.