Riserless core bread oven

[fuegos]

Before i begin i would like to thank everyone on this forum & in the wider Rocket Stove community for all the hours of research & experementation so freely shared but especially Matt Walker for the riserless core & the advice & encouragement given to me & others.



First a little background .We're off grid in a remote mountainous region of Spain , been here for nearly 20 years & have been baking at home for a long time.Our philosophy is to live lightly ( & cheaply! ) , re using & improvising . Solar power , milling our own timber & generally building things from what we have is a big part of our life here so getting a copy of the Rocket stove book by Ianto Evans & Leslie Jackson got me thinking.Although we have unlimited firewood here we built a well insulated small wooden cabin but a RMH just didn't seem practical or necessary given the local climate.So after reluctantly abandoning the idea of a RMH a few years later we managed to get a load of second hand fire bricks from an old water mill that had a bread oven - something its self that warrants another post - & decided that we would build a conventional barrel arch bread /pizza oven .Well that was the plan & a site was cleared & a stone base was built but then for various reasons the project stalled for 2 years...

Once i saw Matt Walkers outdoor oven video i decided to go for a riserless core.Searching through the threads on this forum gave additional inspiration , the post by Bram & his sketchup drawing were particularly helpful , but bad weather & of course the Covid situation has meant that the build has taken more than 2 months & it's still not finished.

The bricks we used are old hand made ones & the dimensions are slightly different to modern ones - 25 cm X 12 x 5.5 . the firebox is 50 cm x 20 x 25 the venturi is 70 mm , the oven chamber is 55cm x 50 x 50 .As you can see from the photos the firebox was going to be wider but i miscalculated & had to narrow it so the oven floorbricks had a smaller span.I decided against secondary air because the confinement meant getting any metalwork done was impossible. The lightweight bricks on the outside are really cheap here & of course insulating.The mortar is 3:1 sharp sand & clay , dug out of the ground when we excavated to build the footing of a new compost toilet.It appears to be almost 100% clay as the pucks we made dried & were the fired in our woodstove without cracking.After various test samples we cast the oven roof slab in place a arlite (1) sand (2) /clay((1) mix.There was some cracking so we re finished the top with a screed of clay sand mortar - 3:1 On top of this weve poured loose arlite for more insulation .The oven door is faced on the inside with aluminium tread plate & fits tight top and bottom but isn't air tight .Maybe an angle iron frame with fiberglass rope wolud be an improvement? maybe i'll try the rope on this door ?

To finish off the outside i'm thinking of doing a scratchcoat of clay/sand & then a lime mortar on top to waterproof , the idea being that if need to rebuild i can re use the bricks.

The first firing was with a small amount of kindling , it was really easy to light & soon started to roar, going smokeless very soon.

Subsequent firings have confirmed for me that this is indeed a powerful core as demonstrated yesterday when i got carried away , filled the firebox with a mix of pine & holm oak & and manged to burn the bread !

So far so good.....

photos.app.goo.gl/FuLfeHkSB3oc14MP9

[szczepanek]

Hi Fuegos,
What a wonderful thing you've shared! And nicely documented, too!
I'm very interested in how it performs. Any info about the temperature inside it, or the time taken to make it hot and to bake a pizza, I'll follow it closely
Thank you and bon appetit!

[fuegos]

hello szczepanek & thanks for the kind words.At the moment i've no way of measuring the temperature & we've only fired it 4 times. The last firing started with 2.5 KG of pine & oak lighting at 10.40. we started with a casserole at 11.00 & put the bread rolls in at 13.15 , cooked by 13.50 another 2 KG of wood was added - about 1 third oak 2/3 pine & the casserole went back in.By 19.00 we took it out to eat & the oven was warm to the touch until 23.00.A previous firing was 2 loads of wood one after the other & the exit from the riser into the oven was burnt clean so i think that pizza would be cooked in about 2 - 3 minutes !
It?s very easy to light & it seems the best way is to use plenty of kindling & add the wood slowly until heat builds up.I'm burning without a door until the load is mostly burnt.

[fuegos]

We've been firing the oven every 2 days but we are still learning with every load.We now have an oven thermometer which makes baking easier but the timing is still a little tricky ,i suppose experience will overcome this.As the load burns out , with just embers in the firebox the oven is between 160 - 180 C . With just 2-3 3 CM diameter pine sticks the temps will quickly rise to 240 - 260 C & will fall back to 180 within 20 - 30 mns.we've been baking rolls on a tray -about 20 mins & sourdough in a dutch oven so the falloff in temps is actually ideal.Just adding one stick of wood at a time will keep the temps at the desired range.The firebox door is a sheet of aluminium treadplate with a wooden handle held in place with a brick.This seems to slow the burn & probably reflects heat back into the firebox.The ratio of firewood is now about 80/20 pine & holm oak , branchwood between 2 to 8 CM .I'm using more kindling to start & with a little blowing it goes smokeless really quickly.
so far so good....

[fuegos]

I finally got round to finishing the outside at the end of July. The clay/sand scratch coat worked out fine and the lime mortar stuck to it no problem with proper wetting down between coats.Lime mortar needs to dry out slowly to cure properly and this was a concern with the high ambient temperatures so i wrapped the whole oven in plastic sheet and continued to wet down for a few days after.There has been some cracking but i'm ok with that , just see them as expansion joints ! they're almost invisible when the oven is cold.In retrospect making it a true double skin would have helped , using a mesh as well .Also the lime i used was NHL 5 , as NHL 3.5 would have been more suitable but i could't get any. The wooden door handle , as expected , didn't last long and was replaced with a long threaded rod and a stainless steel tube that works really well , cool enough to use without gloves. Also i'm firing differently .I now go for a full load from the start , mostly round pine sticks from 2-3 cm to 6-8 cm .I then use split firewood in the second load with just 1 or 2 pieces of oak.When the flames die down i block the chimney in the oven with a baking tray and this sees the temps up to 240 - 250 C after about 10 to 15 minutes .Iv'e found that this temperature drops fairly quickly so i now unblock the chimney after 15 mins and do a last half/third load with some small pine sticks 2 - 4 cm. This takes the temperature up to 260 - 290 C.Again i block the chimney exit & preheat the Dutch oven to bake soda bred which takes 20 mins .At this stage opening the door bleeds off a bit of temp quite quickly so after the soda bread it's at about 240 c - 250 c ideal for baking the sourdough .Next up is the Dutch oven again with a stew , curry or something else .As the temps drop further it's ideal for a onion tart or onion bhajis.The space below the roof has a door at the back for plate warming , drying herbs etc.So between 6 to 8 KG of wood can bake enough bread for 5 days and lunch/ dinner for about 2 or 3 .not bad .
I still haven't fitted secondary air and have had to do a few repairs here and there.Making the core and the oven chamber out of dense firebrick was a pragmatic choice at the start but has turned out out be ideal for an oven.In retrospect even more insulation on the outside would have been a good idea.Overall it's exceeded our expectations and made an important difference to us as our propane bill has been dramatically cut down.All i need to do now is work out how to build a core to run our propane fridge ;-)

photos.google.com/album/AF1QipMuEuWpZ4FNUEzLVC8cRW80FQ6xL08FpylzdE4U

[hof]

What about smoke? 

You've got a long tunnel after port. How is influences on combustion?

[fuegos]

Nov 18, 2021 12:06:57 GMT -8 hof said:

What about smoke? 

You've got a long tunnel after port. How is influences on combustion?

it goes smokeless about 2 minutes after startup.the long tunnel is basically a riser & works fine.As an oven or cookstove having a low compact core means you can have a cooktop or oven at a reasonable height without having the firebox right on the floor.