Experimental Norse-Kiwi Hybrid Oven!

[Wildflower]

Hello from NZ, where, after a lot of tinkering and economizing (unfortunately firebricks are $7 a pop here!), I've decided to try out a hybrid - half discarded Jotul cast-iron stove from Norway, half dodgy masonry-novice barrel-vault.

I've read a lot about different types of issues on this forum (including the heating differentials between iron and brick), but I'm hoping that with a bit of luck the thing will work.

I've attached some photos of the site and the base being poured...trying to keep the kids out of the concrete was the toughest task! Next I'm planning on vermicrete or perlcrete under hearth insulation.

I think this build might provide some entertainment for all of the people out t here who (to their deserving credit) have built such amazing and beautifully masterful ovens!

Cheers!

[jeeppiper]

Re: Experimental Norse-Kiwi Hybrid Oven!

Looks like a winner! Keep the photos coming!

[Greenman]

Re: Experimental Norse-Kiwi Hybrid Oven!

Be interesting to follow your progress. It is something very different but everything is worth a crack. $7 for firebricks is a bit rough. I thought that since there would have been more call for fireplaces and things in the land of the long white cloud that they might be a bit more reasonable.

Like Jeeppiper said, keep the photos coming.

[cobblerdave]

Re: Experimental Norse-Kiwi Hybrid Oven!

G'day Wildflower
Ive been looking at your pic of the norse firebox and thinking of how I would convert it into an oven of sorts.
Internal Chimney...blank it off. you don't want the heat to escape straight out of the oven, you want it to linger around and exit the door so the Mass of the oven is heated. you can always build one on the front externally.

Oven height to door height..... with wanting to get the most out of the heat before it exits the oven you'll want the door to be a smit lower than 2/3 of the height of the roof inside your oven. From the pics it looks more like 4/5s.
I recon a layer of Pearlite/cement inside the oven up to the bottom of the current door. A layer of Pressed Clay Pavers on this to form you oven floor. This should get this closer.

Oven Mass..... The steel will heat up fast and cool down just as fast. A layer of material to store this heat in so its not wasted and give you extended and steady cooking is needed. Cladding the oven in a lime rich cement mix could work. A layer of brick or pavers is another. Roughly 50 mm to 100 mm is usable.

Insulation..... Now you have a mass to store heat in you will need to stoping it from escaping (and burning little fingers) so an insulation layer is needed under and over the oven. Its important, if nothing else is perfect this will go a long way to redressing the balance. Probably pearlite cement would be good and cheaply available.
Anyway just some ideas you might find useful

Regards Dave

[Wildflower]

Re: Experimental Norse-Kiwi Hybrid Oven!

Hey there,
Thanks for the posts, and Dave, thanks for taking further interest!
My research (primarily based on this website) suggested that this MAY work, and therefore my plan at the moment is:

Pour cement "frame" for the vermicrete insulation. This will be about 150mm thick, and come inside the oven and raise the floor of the oven by about 20mm. This, plus the height of the firebrick placed on top, leaves an opening height of 230mm. Applying the magic factor, that would mean an ideal internal dome height of 365mm. Does this sound about right?

To lower the internal height of the cast iron oven (which will be the front third of the oven), I'm thinking of lining it with firebricks (two on their narrow side at each side, and then 4 of so over the top, balanced on flat steel rectangular pieces (not mortared, so expansion should not pose a problem?). There will be a gap under the outlet for the flue.


The back two thirds of the oven will be composed of two arches of firebricks (a la Annie's M's oven), with the usual back wall. The height of this arch would be 365mm. The floor would extend off to the left of the oven, which would happily result in an off-set door, so I could put the fire/wood to one side while cooking.

The walls of the bricked part of the oven would be supported with 25mm ceramic fiberboard backed against grills from the dump pushed up against the rebar rods I've pre cemented at (hopefully) the right spots. This may help the no doubt dodgily built walls from collapsing under the forces of the arch.

So, lining the cast iron stove with firebricks will hopefully increase the thermal mass and make the door/oven height dimensions within cooee. Then, to insulation: I was thinking of putting a few layers of cermaic fibre blanket over the whole lot, then wrapping in chicken wire, then a few layers of stucco. Vermiculite is $70 for 100 L bag here - so not a cheap option for insulation. Over the dome/arch, I would also use the ceramic blanket and chicken wire/stucco.

I've got a good bit of flue with a heavy cast iron damper within it. I was going to put that over the chimney opening, so that I can completely close off the oven.

Last of all, I'm planning on a curved overhanging roof a bit like Fornax Hominus' oven in Canada.

Phew! Makes me realise how much work we've got ahead of us. I see plenty more trips to the recyclers/dump ahead of us!

Any input/ideas and humor appreciated!
Cheers,
Wildflower.

[cobblerdave]

Re: Experimental Norse-Kiwi Hybrid Oven!

G'day Wildflower
Sounds like you have a plan on the go already
I placed the thermal mass on the outside of the iron of the oven due to space.
How big a hearth floor do you end up with inside?
regards Dave

[Wildflower]

Re: Experimental Norse-Kiwi Hybrid Oven!

Hi Dave,
I guess it's a plan of sorts!
Anyway, the way I had envisaged it, the oven would act a bit like the entrance arch in the normal ovens, the main baking would be done out the back.
The internal width of the oven means four bricks can lie across it. With the two bricks on each side lining the oven, the width at the front is 310mm. After that, the oven cooking surface opens out to a width of 590mm. The depth of the cooking surface is 690mm.
There are a few photos here that show the basic idea with the bricks laid out on a board.
Just waiting now to pour the vermicrete under-hearth pad!
Cheers,
Zoe.

[Greenman]

Re: Experimental Norse-Kiwi Hybrid Oven!

Now it is starting to make good sense. Watching with great interest.

[cobblerdave]

Re: Experimental Norse-Kiwi Hybrid Oven!

G'day wildflower
..... Yes that makes sense now. That's a brilliant idea, making the oven your entrance way .... Sorry I just didnt see that
Regards dave

[v12spirit]

Re: Experimental Norse-Kiwi Hybrid Oven!

Hi wildflower,
Interesting build. I have already designed my steel oven and built a cardboard replica for it. Ready to go to the iron fabricator to make it out of steel. I was thinking of making it hybrid to the sake of thermal mass. What is the thickness of the walls of your steel stove?

[cobblerdave]

Re: Experimental Norse-Kiwi Hybrid Oven!

To lower the internal height of the cast iron oven (which will be the front third of the oven), I'm thinking of lining it with firebricks (two on their narrow side at each side, and then 4 of so over the top, balanced on flat steel rectangular pieces (not mortared, so expansion should not pose a problem?). There will be a gap under the outlet for the flue.

G'day
The flat bar concerns me a bit is.... It likely to bend and sag especially in the heat. You much better to use angle iron the shape gives it its strength. My entrance and chimney are supported on two pieces of angle and have been for 4 years now. Not too much rust to date but they will need replacing eventually. But you aware of that and are planning for it.... Great
Regards dave

[Wildflower]

Re: Experimental Norse-Kiwi Hybrid Oven!

Rightio! Well, things have gone pretty well, and on top of the cement slab I formed up a cement border into which I could pour the vermicrete hearth insulation. Of course I made this border too low, so I had a go at my first ever bricks and lay a row on top. This was quite fun and apart from the mortar falling off the ends of the bricks when I was trying to "butter" them (ha!), it all went pretty smoothly. Still, it made me wonder about how I'll go with mortaring the firebricks..yikes. Anyway, I ended up with 15cm plus of vermicrete. It's fairly flat, but I'm wondering if it would be a good idea to
a. use fire clay and sand on top to level or
b. spread a layer of homebrew mortar on top to make it smooth and level, and then the fireclay and sand
?
And also, am I right in the impression that the hearth bricks should NOT be mortared in place, and that the wall bricks should NOT be mortared to the hearth bricks?

Many thanks,
Zoe.

[Wildflower]

Re: Experimental Norse-Kiwi Hybrid Oven!

Thanks for the hint about the use of angle-iron instead of flat iron - I had no idea!

[cobblerdave]

Re: Experimental Norse-Kiwi Hybrid Oven!

G'day Zoe
You right you shouldn't mortar down the hearth brick or the first layer of the vault. The hearth can be leveled on a layer of clay and sand alright. The first layer of vault bricks mortared to each other but not down.
As for the bricklaying well .... It so happens I'm "masonry impaired" so I understand exactly what you mean.
I can give a few a few things that might help.
Vinegar and rubber gloves. If you find it hard to use a trowel you'll be tempted to use you fingers. Don't . Get yourself some strong rubber gloves and if you end up with mortar burns wash in vinegar. It will not fix the damage but will take away the sting.
Gauging trowel. Its not a brick trowel at all but a plastering tool. But its small and has a round end and heaps easy to use for the mug bricklayer.
Mix small batches of mortar so you have no pressure to lay bricks fast. A 20 ltre plastic bucket and a paint mixer on the end of an electric drill will do it. Let the mortar sit for a while after mixing sometimes it soaks up a little more water than you think it will.
Soak some bricks as you go in a bucket, it will stop them from drawing the water out of the mix.
The fireclay is the bit that makes the mortar a little easier to stick to the brick and let's you squish it into position if the mortar does crack away . Stop. Remove the brick, scape off the mortar and do it again. Don't wash the brick, the remaining mortar left makes it work the secound time much better.
Hope something here helps
Regards dave

[Wildflower]

Re: Experimental Norse-Kiwi Hybrid Oven!

After a winter hiatus, it's oven-building time again!!!
Mixed up t he homebrew with a paint/drill tool and then went to work, built up the two rows of the walls. Looking OK, but was surprised at how stressful the whole caper was!
The mortar may be a little on the thick side, but it is what it is. I think I'll leave it a week before starting on the arches / vault.
Thanks for the advice, CobblerDave.
Now it's time to workout how to do those pesky arches...