Ivar Oudewortel

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since Sep 18, 2014
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Recent posts by Ivar Oudewortel

Dear Daniel and John (and other permies)

Thanks for the reply, I have checked out the Rumsfort fire box but that doesn’t cut it for me.
The cast iron kettle is 40 cm in diameter and the grill grid is 120 cm x 60 cm. So the shallow fire box has to be at least 60 cm deep, inner size.
As you can see on the pictures, I have started the first batch of cob on top of the urbanite. I might decide to put some more cob on the wooden deck to ingrease the size of the of the actual pit, inner size.

That aside, my main concern stil is, the different expansion/ shrinking rates of the different materials I want to use in the cob wall.

Since glass and cob are both made of sand I expect not too much difference in those but still.

Daniel Ray, what a beautifull kitchen you guys made, big up!
Bit bigger of a project I have started but who knows in the future I might be able to pull something off like that.
Question, is the firebox below just heating the oven by radiation or are the fumes passing through the oven compartment?

I have made a temporary roof out of plastic because I ‘m not sure about the roof yet. I might opt for extending the current shelter roof.
I would much rather build it completely out of cob, chimney and all.
Hoping to seal the outside with boiled line sead oil for weather protection.
Given the fact it tends to rain quite a bit in the Netherlands that might be a bold or plain stupid choice.
It would look awesome though, even if its just for three years.

Ill udate when I’ve got some work done.
Pics are not spectaculair yet.

Thanks in advance.

Be good!
5 months ago
I know this tread is a bit old but I ‘m hoping someone still reads this sometimes. (As I did).
After a couple of days (and some nights below 0 degrees celsius)
The sample looked like the first pic.
It seems to me that there’s hardly any sand in this soil sample.
I mixed a batch of cob adding 5 buckets of sand to one bucked of this soil/clay.
Seemed pretty good cob to me, although I m not so much expierienxed in cob.
The hold of the mix was pretty good even without strawl.
See 2nd pic.

So my questions are...
1. Did I misread the jartest results or does my sample indeed have very few sand in it.
2. If so, should I add more sand to the mix to prepare cob for building.
3. What effect would a too high percentage of clay in the cob have on my fireplace build out of cob?

Thanks permies in advance, looking dorward to your thoughts.

Kind regards from the Netherlands.

5 months ago
Dear permies,

I want to build a fireplace under an outdoor shed.
The goal is both open fire for Dutch Oven, cast iron kettle cooking and or bbq nights, you know, the good stuff.
On the end of the existing open shed, no walls just over roofed, this fire place is about to emerge.
The idea is to make a round-ish cob wall, place a roof with overhang on the wall and build a chimney on top of the roof. (Haven’t got a clue on the chimney construction yet, ideas are welcome)

Foundation is layed by some urbanite (smashed bricks) covered with cob.
Since the height of the wall is going to be close to 2.5 meters, I m going to need a fair amount of cob.
Reducing the total amount by adding bottles, cans or bricks in the wall is very tempting.
Since the cobwall is esentially a fireplace, pretty big temperature changes are to be expected.
Adding different materials in this wall, all having their own expansion/ shrinking rates concerns me slightly.
Especially given the fact that the wall is loadbarying for the roofstructure as well as a fair mass itself, I don’t want the risk of the walls falling down due to big cracks.
Hurting my toes or worse, spoiling my meal.
I can imagine that the base of the fireplace up to say 1 meter, takes the biggest temperature swings and therefore should be 100% cob. Above that I would love to use bottles and cans, even if its just for the beauty of the end result.

Hope anyone has some thoughts about this?

Thanks in advance and love to hear from you guys and girls.

Kind regards, Ivar

5 months ago
Hi folks,

Ivar from Arnhem here.
I just came back from Wageningen where a group of people living in a forrest as permie as they can.
They started building a earthship-ish struckture and my roll is building a Rocket Mass Heater in there.
Fantastic site and very challenging project for me aswelk hence its my first RMH I ever build.

Will post a link later with the building process documented.
They have a permagarden allready and live more or less independed / off grid.
Check out www.partijvoordeplanten.nl for some info about them.

As soon as I have a bit more time I will check out your projects too.

Saludos de Arnhem.
3 years ago
Hi all,

I came a long way since last year, yes I bought the book and yes I red my eyes out and saw a million of Utube vids...

Here's a pic of my first serious attampy to build a RMH.
Can't wait to have it finnished and see how it performs.
Thanks all and Al.
3 years ago
In adition to previous post, it seems to me that the heatriser schould be longer and more narrow.
What are your thoughts on that?
The scroch marks you're right about.
It realy amazed me how high the temperatures get in this setting. I planned to cover it all in cob (the lower part) to avoid my board catching flame.
Maybe using a double wall insulated burn tunnel will be better and then cover it with cob.

My objective is to construct a small setup of this system for use in gardens, cook something or just enjoy the colder getting evenings outside.
I want to spend as little as possible and upcycle as much "waste" as I can.
A garden heater so to say.
4 years ago
Hi Al,

As you can see it kind of evolved from a pocket rocket to a RTMH.
I tend to to before I read a lot. Met some challanges as I went along.

The heat riser is also made of cans, double walled insulated cans. See pic below.
I used rockwool (cause it was free to me) and found that it isn't suitable for those temperatures.
First challenge.
I didn t get a good draft, probarbly because the heatriser is not long enough compared to the burn tunnel.
Challenge two.
And now the metal fatique, challenge three is, thanks for that, looring.
I wanted to build it all out of free, waste materials.

Gonna tinker on and make some adjustments and share what I find.

Thanks for the input.

4 years ago
I'm investigating which type of oven I should build as my first cob project.
Reading a lot here and there I would like to ask something about the pro's and con's of a single and a double chamber oven.
If I understood this correctly the benefits of a second chamber is mostly a cleaner burn/ less smoke and a little less time to bring the oven to baking temp.

Better fuel efficientcy of which is spoken in the video seems to me comming only from the shorter timespan you need to pre heat the oven.
Or does the afterburning of the fumes in the chimney also contributes to the temp. in the baking chamber?
Its obvious it looses a lot of energy in the chimney.

Currently testing a rocket stove termal mass heater build out of cans and defenetly thinking about a RSTMH in combination with oven.

Thanks all contributors to this and many other forums for sharing your expiriences.

Attached my tin tinkering project.

4 years ago