Gerry Parent

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Big Welcome to Permies Brett!

First off, that is a very impressive piece of functional artwork you've built!
Not having very much experience with lime plaster, I don't want to steer you in the wrong direction, but I do know that its often a good idea to light up your stove several times until the cob completely dries (and make pizza at the same time of course!). What this does is it will cause any cracks (if any) to form, then you can patch them before the final coat which will cover up all the imperfections made by the repairs.
Not a foolproof method, but certainly one that has worked for me.

Keep us posted, we like pictures!

You are about to enter another dimension, a dimension not only of sight and sound but of mind. A journey into a wondrous land of imagination. Next stop, the The Stove Chat Zone!

Today at noon PST with our favourite host Matt Walker

There's also one at Wheaton Labs. See here for video: rocket hot water heater

I watched his interview also and was impressed by the amount of information he presented that made a lot of sense. Highly recommend for people to watch it.

Hi Peter,   This winter I made a test block about 3'x2'x3" from Light Straw Clay. Both locally sourced reeds and clay.  It too was extremely heavy so I kind of wonder at the "Light" part of the name!
When it did finally dry though (about 3 weeks later) it did get somewhat lighter.
However, if you've ever slung bales of hay around you know they are anything but light. Maybe 40-50 pounds per bundle so even without the clay or other things mixed in, its always going to be pretty heavy.
To speed drying time, I would suggest making your mold much thinner in diameter to increase the surface area per block thereby reducing the drying time considerably.
At some point in time, it would be interesting if you could cut your block in half and see how wet it still is inside.

The sand and silt are not acting in any way as a binder so removing as much as you can would help reduce weight. The extra processing time may not be worth the effort though for the little it may contribute to the overall weight savings.

That would be a cool experiment to try using lime just for science, but because even homemade lime is much more labour and fuel intensive than processing local clay, it also may not be worth it and instead save it instead for a plaster coat where it could be more beneficial. Just guessing here though.

Love to hear about all your findings.  

Hi Brian,   Here is a list of RMH builders, some of which are located in Europe:  List-Rocket-Mass-Heater-Builders

Good luck in making your dreams come true.

I would agree with Thomas on the safety factor. An open system is way more safer and there are many people that have built one with great results.
I suspect your getting such poor draft due to the fact that you've plugged up about 1/4 of the heat riser with the coil, adding a whole lot of drag to slow down combustion.

Awesome picture as usual to describe what you mean Peter!

I don't know what regulations consider to be a safe distance above your barrel but my test has always been to feel the surface and if you can't comfortably hold your hand there, then its too hot and definitely needs some kind of protection. A cf board cut to fit inside the top of the barrel could work, a heat shield suspended from the ceiling to dissipate the heat, or the simplest way would be to just put a bunch of rocks on the top of the barrel. They not only would dissipate but also hold onto the heat. Leave a little room for a kettle if desired.

Good tip on barrel thickness. Didn't know that.

I would say it depends on a few factors Peter.  First, is your exhaust temps high enough to extract more heat and so that you don't loose too much draft and have potential smoke-back issues, hard cold starts etc.?
My elevation gain was made from mass - Yours will be bare metal which will obviously transfer the heat much quicker, so going back to my first question of current exhaust temps and how much they can be lowered will affect whether mass or metal should be used, if at all.
Matt Walker recently said in a stove chat episode that roughly 200F was a good exhaust temp for an effective all season draft whereas 300F was giving up too much. This number is the centre of the exhaust stream, not surface temps. I've even had it lower than this with no draft problems but of course it really depends a lot on so many factors like wind direction, temperature differential, climate, humidity, length of vertical exhaust pipe etc...etc... Each situation is totally unique.

Also, if you did go with the half barrel idea and weld them together, would you still be able to lift it off for cleaning/inspection?..... will Mimi be able to help you out?
However, if you put the half barrel on the bottom and remove its top, you could use a clamp to secure them together (assuming they are compatible) and readjust the seal at the bottom to accommodate a rimless base. This would solve the weight issue.
Note: Having 1 1/2 barrels will mean that that it will direct the instant radiant heat higher up which won't be as noticeable at body height if this is not a problem.

All in all, its a simple modification and relatively easy to switch back if it doesn't work out for you so I don't think you can go wrong either way...after all your a scientist right?