Matt Walker tiny cookstove build in Portugal

eva guo wrote: Have no idea how to mortar.

This might inspire you...

Burra Maluca wrote:This might inspire you...

Inspire, yes! Allow me to emulate - not likely! I think I would want to start with straight clay slip, as it would be easier to undo when I bugger it all up! Keeping things lined up is critical, and the Layer is clearly very experienced.

Lovely video though - peaceful and proficient!

Jay Angler wrote:«Inspire, yes! Allow me to emulate - not likely! I think I would want to start with straight clay slip, as it would be easier to undo when I bugger it all up! Keeping things lined up is critical, and the Layer is clearly very experienced. !

We're using refractory mortar for ours because we didn't manage to source fire clay in time, but Matt's recommended mortar is  three parts sand to one part fireclay. Maybe with screened fly ash added if you have any available. It might be fun to just build a really simple one to play with and practice the required skills. I mean, I cheat and let Austin do it. But I might have a go at some bricklaying when we get as far as building the bench.

Meanwhile the dragons are dropping hints about how he should be doing things...

I found a couple of youtube videos that Matt Walker made about the actual building process and about mortar.

This is a wood-fired brick oven, not the tiny cookstove, but the basic techniques of building are the same. The time-lapse of the building itself starts about twelve minutes in, but the rest is worth a listen, too.



This is the discussion on mortar for rocket and masonry stoves.



And this is a video of a stone house renovation project that both my son, Alan, and Austin were involved with. I strongly suspect that one of my dragons was involved in putting the pretty burn-patterns on the woodwork, too...



Ah yes, that young red one is obsessed with fire...

Been a bit busy so it took a while to get to this stage of the rocket stove build.  The former is going to stay under the arch for now while I build above it.  Predictably, the spur-of-the-moment decision to make an arch added quite a bit more work, including cutting special sized bricks or it was gonna be too tall.

That arch is lovely, Austin! I love arches - both from the artistic and the physics perspectives. I expect you will enjoy that arch for a very long time.

Jay Angler wrote: I expect you will enjoy that arch for a very long time.

I think we will!

I certainly learned more about Isambard Kingdom Brunel and the science of arches over the last week or so than I have in the rest of my life...



I'll make a longer post tomorrow with more photos of the building process. I took a few bits of video too. This one is my favourite, showing how arch building can be interrupted by the unexpected arrival of the long-awaited car-go train...

Just as an aside, Brunel is one of my heroes.  When he was building the Great Western railway in the 1830s-1840s, trains typically did about 30 mph.  Brunel was enough of an engineer to predict that they would get faster and that hills and curves would become the limiting factor for speed.  That's why the elliptical arch over the Thames, so as not to introduce an unwanted gradient, yet still not restrict the river bed.  My arch though is a simple radius.  There isn't really space for anything more clever.

And to show just HOW much of a visionary he was, the main line from London to Bristol was laid out to allow speeds up to 150 mph.  When they introduced the HST in the 1970s which could routinely run at 125 mph, no work was needed on the track to allow running at that speed.

The same principles were adopted in Japan with the Shinkansen - for a really fast train, track geometry becomes the defining factor.  

I just want to share a few photos and memories of the arch building.

This is the original walker tiny cook stove.



Austin asked me about the stone above the oven door. I thought he meant the pretty inset bit of ornamental stone so I said I wasn't bothered about it as whilst I love stone, I like it to be functional first and ornamental as an extra. He actually meant the stone that bridged the gap above the oven door, which can be done with either stone or a bit of angle iron. But hey...

Anyway, having been told that I wasn't fussed about it (even if I did mean something else) he immediately started to dream of building arches.

That's what comes of having a physics degree and being an engineer I guess. And who am I to stop him!

Anyway, I love arches.

Now we have to design the arch to fit, because the only space available for it is the equivalent of two layers of brick, so we need to make sure it works, and looks good too.

Iggy immediately got to work, as he's the engineer of the dragon family. Rosa helped by supplying a bit of pink thread for measuring purposes. She said five bricks would look silly and clunky. And it had to be an odd number so there is one right at the top of the arch. So seven seemed perfect.

And this is what they came up with. I think Austin helped too...



A bit of mdf was invested in to make the former, and the shape was transferred from the dragons' design.



Two sides are needed to make the former.



Fitting it into place.



It also had some appropriately sized blocks of wood fixed between them to hold them steady at the right distance apart.

We figured that if we made it well, it can be used for any future builds we do.



Then the dragons made a quick mock-up of the design to check it all worked.

I don't want it actually sticking out like that though, else I'll constantly be bumping my knees on it when I'm using the stovetop to cook on.



Note from Austin

The bricks needed extra cutting to make the overall height within spec. They're set on edge like in the mock-up but cut to 4¼" long so the same as the width of the normal bricks. Then they're cut down to be square, at the depth of the normal brick which is 2¾". A bit of a faff, but I like the way it turned out

And a quick action video...



Lots of cuts to make, but we're getting there...



Roxa wants to help, but I think Austin wants to do it all himself.

Because the arch is shallow, it's important to support the ends of it so it doesn't try to flatten out. So there are two specially cut and shaped bricks in position to make sure they stay in place.





A wipe down with a damp sponge to remove surplus mortar, and it's just about perfect!





Another note from Austin

gonna leave the former there for now, it can come out later.
It also needs to be flush with the main front face so as to make it easier to fit the oven door

One more layer of brick to do, which will involve a LOT of cutting to fit around the arch, then it's time to build the core. I've issued instructions to come home with a supply of firebrick and perlite at the earliest available opportunity so we have supplies in ready.

Watch this space!

Austin & Burra;
Your build is looking great!
The Arch is a fine addition!
After watching Austin using the handheld grinder to make cuts in the brick, I thought I would mention using a sliding chop saw (or a sliding compound saw) with a diamond blade.
Cuts are super fast and very straight.  Also, are you soaking your bricks in water, a few minutes before cutting and mortaring?
Keep up the good work!

Thanks so much for sharing this build Burra and Austin. I do love the idea of the tiny cookstove....Your's is looking beautiful! Love the arch.

Update time again!   Got layer 6 finished with the last and trickiest of the custom brick cuts for the arch.  

We had a piece of steel sheet in the shed but it turned out on closer inspection to be a bit thin to be the core support, so we tooled off to the steel supply place and bought a sheet of 3mm (about 11swg) which will do the job nicely.  Note to others: hand cutting 3mm steel sheet with an angle grinder is a bit like work, if your steel supplier has the ability to cut it (such as a guillotine) then it's worth getting it cut to size.

Anyhoo, here's a picture of layer 6 completed with the core support resting on top.  The dragons seem to think that it needs holding down, obviously they've not tried to lift it.  Or maybe they're cooking up some nefarious plot again.
(on the left are 3 bricks for layer 7; they are there as I had some mortar left over to use up)

Here's a video of the sheet being cut to size.

Great fun, and the dragons loved it. Especially that young red one...



I feel honour bound to mention that those sparks can cause problems. The fire last year was started by a neighbour cutting metal with a grinder like this up on his roof. The sparks set fire to dry grass, he noticed and jumped down off the ladder to put it out, managed to fall and injure himself, the fire spread to his wood-pile, then the wood-pile went up like something out of a nightmare with an incredible rocketing noise and spewed burning embers half a mile up into the air. The wind was strong that day, and blowing in our direction, and we lost a lot of stuff, including our tractor and very nearly my son's house.

But anyway, back to the rocket mass heater build...

After the sheet was put in place, the dragons took it over and Rosa, the little pink dragon who is rather overly domesticated and likes to play at keeping house, brought them a picnic, complete with a supply of apples. I think the excuse was we needed a core next and they think the ones in the apples might help.



I suspect it was just an excuse actually...

Anyway, a supply of firebricks had also arrived, so Austin has been laying them out in a mock-up to see what adjustments have to be made to the plan to allow for the different sized bricks here rather the ones Matt used in America.

Serra, the most slim-line and serpentine of the dragons, has been volunteered by the other dragons to test the path of the hot air in the build so far, and ended up getting a bit stuck in the port of the mock-up core...



It was a bit of a squeeze for the poor old girl.



I think she's doing it!



When she did manage to get through, she spun around six times at the most incredible speed then shot upwards and disappeared, so far without trace.

Maybe she completely combusted or something.

Never can tell with dragons...

Burra Maluca wrote: I feel honour bound to mention that those sparks can cause problems. The fire last year was started by a neighbour cutting metal with a grinder like this up on his roof. The sparks set fire to dry grass, he noticed and jumped down off the ladder to put it out, managed to fall and injure himself, the fire spread to his wood-pile, then the wood-pile went up like something out of a nightmare with an incredible rocketing noise and spewed burning embers half a mile up into the air. The wind was strong that day, and blowing in our direction, and we lost a lot of stuff, including our tractor and very nearly my son's house.  

This is a good reminder to people. Burra and Austen have done a lot to help their land recover from the fire. Many places have a history of fires helping the land, but that was when the vegetation was adapted to "The Fire Cycle". Fire would open up forest and create meadows that had much more biodiversity than the forest could support on its own. An obvious example in North America is "Fireweed" which is adored by bees and grew in profusion after a fire. Humans have mucked up a lot of that cycle. Personally, here in North America and in parts of Northern Europe, people learning to work with the Beaver People would be a big help, but Humans tend to want things their way, and Beavers have much different opinions on the same matters. We need more Chinampas and fewer multi-acre dry-land farms, if we want to work with Beavers.

After the sheet was put in place, the dragons took it over and Rosa, the little pink dragon who is rather overly domesticated and likes to play at keeping house, brought them a picnic, complete with a supply of apples. I think the excuse was we needed a core next and they think the ones in the apples might help.

So long as Rosa just thinks you need a "stove core" and not "apple cores" to toss here on permies because people aren't following our "be nice" rule, Rosa can have lots of apples!

Hi Burra, thank you for documenting your build so well, it is coming along nicely and now you are getting to the more exciting bits!
As you are obviously a dragon fan, I thought you might like to see my own dragon.
I just finished it early this year.

Oh now that is a beautiful dragon!

I admit to being a tad jealous of that mighty beast.

Serra, who seems to have rematerialised, is attempting to claim that there is one just like it lurking in the back of one of the water mines up on the mountain. And is possibly related to her granny, as seen in the photo...



But then Serra, who is after all one of my alter egos, is rather prone to making up silly stories...

She's made me promise to relay some tales of her adventures, but I have the humanure to attend to this morning which is going to take up all available energy I have for a few hours. Hoepfully later!

I think the stories are going to involve CO2 drawdown and photosynthesis and rebirth of dragons, or something...

Well Serra has returned from her travels and is waxing lyrical about her adventures.

Apparently she did indeed completely combust in the core of the rocket mass heater and exited up into the atmosphere in a most ethereal, dragon-like manner.

As she floated in the atmosphere above the house, she looked down at the landscape and remembered how burned it had all been the year before. Just like she was now...



And as she got higher and higher she looked back over her mountain range, which she is named after. Or maybe it is named after her. Or maybe they are one and the same.  Who can tell?



The serra snakes off into the distance, undulating like a dragon's back.

The ethereal Serra cried a little tear as she remembered the conflagration of the trees, burning as she had burned. And then she remembered the work we had done to sow the seeds of restoration.

She had been with me as I had used my tree-planting staff to plant acorns and walnuts and chestnuts and hawthorn and rowan and whatever else I could find up there.



And she had found the first signs of the oak regenerating from the roots...



She remembered her partner, Rubeus, telling her about an old poem about a conflagration of the trees, and how the vanguard of the regeneration process was the alder. And she remembered seeing the tattoo on my back as I had worked.



And as she remembered the burning and the regeneration of the trees on the slopes of her mountain, the balance of her mind began to break down and she heard the old Welsh call to "Dod 'Nôl at fy Nghoed". To come back to your tree. To become wood again.



Having completely combusted, Serra was little more than carbon dioxide and water vapour by this point, and she longed to become a tree again so much that she began to fall to earth again as a rain of tears until she was completely absorbed by the earth. She is, after all, an earth dragon so it is only natural for her.

As soon as she felt the cool earth under her ethereal feet, she became happy again. Literally in her element!



Then she burrowed into the cool earth in search of tree roots so she could become part of a tree again and become whole.



And that is, apparently, according to the stories she's been telling us, where she has been for the last couple of weeks. Pulling herself back together into solid flesh, making sure the trees on the slopes are regenerating nicely, and then returning to her little dragon family to tell us all about it.

She also says that there should be plenty of wood up there for us to gather and use in the rocket mass heater this winter and forevermore to keep us warm.

I guess I should pull myself together a bit and try to get up there one morning to have a look for myself.

In the meantime, we have more stove building to do. Especially that core!

Oh I love that story! "Dod 'Nôl at fy Nghoed" Hmmn, I'll have to learn how to pronounce it! This is how I feel best - in contact with my trees...

Nancy Reading wrote:"Dod 'Nôl at fy Nghoed" Hmmn, I'll have to learn how to pronounce it! This is how I feel best - in contact with my trees...

Hmmm. Well I searched for videos that used the phrase and didn't find anything worth listening to.

I used the read-aloud function on google translate and nearly cried when I heard how bad their version was.

I might attempt to persuade himself to make an exceedingly short video later, in his best 'Welsh Preacher' voice. I know he has one...

Just need to find a suitable tree to pose him under. I suspect Rubeus will want to help, being a full blooded flag-carrying Welsh dragon. All the way from the Welsh Folk museum no less!

And Rock, the Welsh Sheepdog, of course. He gets to photobomb most of my photos and videos after all...

There y'go.

"Dod yn ôl at fy nghoed" - coming back to my trees, or my wood (as in lots of trees), or wood (as in the stuff trees are made of).

With the noble assistance of Austin, an old olive tree, a young pepper tree, a young red dragon fruit plant, Rubeus the Welsh Dragon, and Rock, the Welsh Sheepdog.

And the GAMCOD garden!



I wonder if it's related to the English phrase about being 'out of your tree'?

It's been a bit quiet on the rocket stove front, been busy with worky-work which has the advantage of paying the bills but eats into your time..

Anyway.  This afternoon's exercise was a trial stack of the brick riserless core, to see how it was gonna work out with the available bricks we can get here.  
Also to determine where to put the opening in the outer brick shell which will eventually have the firebox door in it.

Obviously this isn't fully stacked, I have to cut some bricks and will want some fireclay mortar to assemble it for that.  But it shows that it will indeed fit in the available space.


Tomorrow should be able to set the firebox support and restart shell building.

Having got the trial stacking done to check dimensions, on with the build.  Removed the arch former as that could be tricky later, then layer 7 on which holds the core support in place.

The Dragons have come to look at it.  Iggy thinks the bottom oven space makes a nice cave.  Vermelha heard someone say that the firebox goes on that plate, so she's keen to make flames happen there, although that's some way off yet but she's young and keen.



Spot the chameleon seems to have been climbing up from underneath while Rosa and Roxa watch, they seem to be discussing something.

Looking Great Austin!
How could it not with all the inspectors on the job!
Keep up the good work!
You will be cooking on wood in no time!

Am I understanding correctly, that the area under the arch where Iggy is will be an oven space with a door? If so, what will you make it out of?

Similarly, is the mock up stack of bricks going permanently approximately where they are in the picture?  Is the stove top with the cooking holes that was pictured somewhere, going to go on top of those stacked bricks or beside it?

Just wondering how high it all will be in the end?

Kind of a nice, stove-top height

Jay Angler wrote:Am I understanding correctly, that the area under the arch where Iggy is will be an oven space with a door? If so, what will you make it out of?

Himself has worky-work this morning so I'll answer as best I can.

Yes!

That will be an oven with a door. Austin is a welder by trade so I'm expecting a nice door...

Something like this would be awesome...



That one is currently available to buy from wells reclamation but there's not much chance it would be the right size.

Thomas Rubino of dragontechrmh sells batchbox doors, as per the one below.



And also a book on how to build a batchbox door.

I'm hoping Austin will come up with a nice pair of doors that 'match', but will be a bit less industrial looking than Thomas' though obviously not as nice as the cast iron door. Welding simply isn't the same as casting!

It will be made of steel of some sort. No final decision taken yet, but I'm currently eyeing up the rest of the sheet that we cut the support for the core out of.

Out of interest, Iggy is part earth dragon and part fire dragon. Kind of a hybrid. His full name is Igneus, as in hot, volcanic rock. He seems to be checking out the oven area in anticipation of a new arrival...

is the mock up stack of bricks going permanently approximately where they are in the picture?  

Yes! I think part of the reason for the mock-up was to check the precise location and sizing needed for the door.

Is the stove top with the cooking holes that was pictured somewhere, going to go on top of those stacked bricks or beside it?

On top!



The fire goes in that hole at the front of the core, around the corner (where the magic happens) then rises with a vengeance through a gap at the front right of the core. Then it follows a serpentine path to the back, then around the corner to the left, then finally it will plunge down the big chasm on the left - the one that Spot the chameleon is climbing up on the dragony-photo - she got it a bit wrong. We'll have to get Serra to do a better photo-series to demonstrate the proper path in due course.

The height of those bricks on top of the core that create the serpentine path that the very hot air flows along can be tweaked a little to make the perfect height for the top of the stove, and the clay brick shell is built to match.

Just wondering how high it all will be in the end?

I think this video of Matt himself standing next to his one, and talking about cooking on it, will illustrate that better than I could at the moment.



I also caught Serra showing this to all the younger dragons. I have a sneaky feeling that one of the late-night trains might be dropping off a new arrival very soon. It has a lot in it about dragon ecology, relative temperatures of various ovens and fire-boxes and volcanoes, safety aspects of using proper containers made out of appropriate materials, some shots of traditional fire-box doors, and some nice audio of dragonsong.  Enjoy!

Serra was a little concerned that Spot the chameleon was giving the wrong sort of idea about the way the hot air flows in the cookstove, so she wanted to demonstrate.

She explained  how the air that comes up from the fire and snakes its way along above the core and under the stove-top cools a little as it does so, and then it part sinks and is part pushed DOWN the chamber at the side...



...where it emerges into the oven at the bottom.

There she is, entering the oven space to say hello to Iggy!



They certainly do give the impression that they are waiting for someone to arrive.

I heard booping at the station at 9 o'clock this morning and wondered if it meant something, but apparently not. It was just three sisters going past hauling empty wagons.

Not corn, beans and squash, but Cátia, Neuza and Earine.



At least, Cátia and Neuza were hauling. Earine was snoozing by the look of her and having a free ride!

Apparently it's not just Welsh engines who have names!

OK seeing as my shell is now 2 layers above the core support plate, I thought I'd make a start on the core.  However, the sand I started messing with, which is what I would call sharp sand* in the UK (and is what you'd typically use for bricklaying mortar) is a bit coarse and, to actually seal between the bricks is going to require a significantly thicker layer than I was planning to use, dry stacking the bricks I can get pretty close to the required measurements so I'm really looking for a nice thin mortar just to seal between the bricks and make sure they sit upright on the base if the brick itself isn't quite evenly shaped.

I'm gonna look into whether I can get a finer sharp sand, but there's also another option I can readily get and that's "yellow sand" which is what you'd call soft sand and is typically used for making rendering mix using either lime or cement.  That may be a better option for this job.  I think I can also get rock powder, that may be another possibility.

What have other folks used, who have done brick cores? did you dry stack the core?  I'm a little bothered that it might not stay stacked correctly - I'm looking for low maintenance as a factor, and also some bits likely need sealing.

* one of the guys in a building supply yard described it as "made from brita" - and brita is chippings such as you'd use in concrete.  So this sand is crushed rock.

Hi Austin
My Walker core is dry stacked and I feel 100% confident with it.
If your firebricks are new and smooth, dry stacking works great.
As another option.
You can mix straight fire clay and make a clay slip you dip your bricks in.
This would give you a thin layer that would give you a smooth mating surface but no bonding at all.

I agree with Thomas, as long as the bricks are well made they should be very flat and square edged making it easy to dry stack.
However if you prefer to join them with a thin set, super find sand with fondue cement or good clean clay (4-1 mix) will work.
For the sand I can suggest a few sources, play sand used for kids sand pits, fine horticultural sand from garden centres, pure silica sand from builders merchants or kiln dried dust for filling brick paving.
If all those ideas fail then you can sieve course sand but if it is not pure silica sand it will leach salt or other minerals over time.

pretty sure I can get that rock dust they use for paving, there's a lot of granite or marble block paving here.  I might try that.  

The bricks are pretty good for flatness and squareness but I'm kinda perfectionist and some kind of bond feels right.  I did also note that not all the bricks would stack quite how I wanted them so maybe not quite as flat as they look

There are loads of thin, twiggy branches at my son's place from trees that got burned in last year's fire but aren't worth using as fuel for a normal wood burner. So I've been scrounging them to make fuel for the rocket mass heater and have set up a stick-cutting station under the orange tree.

Should keep me out of mischief for the brief time every day it's not too hot for me to be outside...



Fiskar's loppers and a well-marked cut-to-size bit of surplus broomstick are my main tools. Plus a nice garden chair because I can work three times as long if I can sit down.

The sticks are still a bit sooty...



There - one tub of nice dry sticks to fuel the rocket mass heater!



I think I'm going to figure out a way to weigh a tub of wood and then figure out exactly how much weight of (dry) wood we burn a day in the winter.

I guess weather conditions will effect it, and there will be days we don't burn at all if the weather is mild. But it would be good to keep some kind of record if only to compare notes with other people.

'One tub' really isn't accurate when so much of it is thin, twiggy bits that take up space but don't weigh anything.

Hmm that might not be the best fuel, I have never built a Matt Walker stove so I really dont know but I suspect that although  small twigs and thin branches would be good for kindling and loading on top of logs or bigger pieces of wood, but will burn through really fast as there will be a lot of air surrounding the stack that might lead to the fire spreading  downward  very quickly and over fuelling?
Small branches and twigs work well in an open top J tube but in my closed door vortex stove, they are not suitable at all apart from the top kindling layer.
I may be wrong though……

Fox James wrote: I suspect that although  small twigs and thin branches would be good for kindling and loading on top of logs or bigger pieces of wood...

Small branches and twigs work well in an open top J tube but in my closed door vortex stove, they are not suitable at all apart from the top kindling layer.

Well there is still plenty of bigger stuff to cut down, especially some enormous eucalyptus I want to get rid of that burned in the fire and has been standing dead for a year, with green stuff growing like crazy around the bottom. I daresay a trip up there with a chainsaw and the tractor and linkbox can prove productive.  Then we can fiddle around with what we have and find what works best.

I really want to use up as many as we can of those twiggy bits though as they are a fire hazard just lying around the place.

So, kindling at the top, not the bottom. I'm gonna have to get that into my thick head as I've always done it the other way around...

I may be wrong though……

Oooh a challenge! Only one way to find out. Experiments will ensue in due course.

Fox James wrote: small twigs and thin branches ... will burn through really fast as there will be a lot of air surrounding the stack that might lead to the fire spreading  downward  very quickly and over fuelling?

Fox, could you explain a bit more about over fuelling, what it is and why it's not a good thing?

I'm trying to decide whether or not some of my experiments should involve burning just thin stuff on days that we just need a quick burst of heat to bring the temperature up, or whether it's better to do it a different way.

Ages ago, folk would bundle and tie together a number of small diameter sticks to burn as logs. Would this form be appropriate for a batch box?

Overfueling basically means there is too much fuel burning at a given time resulting in unburnt wood gases producing smoke exiting the chimney.
So the idea of a clean burning  rocket stove revolves around producing ideal conditions inside the fire box that allow the wood fuel to completely combust including all the smoke.
However there are certain criteria that need to be applied to get consistent smoke free performance, very often the designer will have tested the stove and offer instructions  about fuel type, size, quantity  etc
Things like leaving the door open during start up or restricting air when running flat out or stacking the wood in a certain fashion.
I am not completely familiar with the Walker stove so I dont know what Mat recommends?  
Adding extra fuel to a hot stove is possibly the most likely cause of overfueling but also loosely  packed or wet wood or too much kindling etc
Stoves that have a viewing window like some of Peters designs or the vortex stove will show up the results of overfueling more so than other types of stove but a sure sign is lots of smoke coming out of the chimney!
I have a video taken during one of my experiments that clearly shows just how dramatic over fuelling can become….  

Time for another update photo:  Layer 9 of the shell is now added and I've started on building the core.   The plan is to complete the first layer of the core and then insulate around it.

Found we had some yellow sand which seems to work well for that, mixed 3:1 with fireclay.  
I find the clay mortar needs to be quite wet, or it dries out super fast before you got the brick where you wanted it :)

The dragons are inspecting.  Vermelha thinks she knows where the fire will be.