Cob in a wooden box?

Hello,

Simple (I hope) question: Is it possible to load cob into a wooden container to form a heater mass.  The "adobe" full cob bench just aesthetically doesn't work for me.

I was building plans for a gravel 6"system on a 2nd story (albeit well-supported) floor build.  Given cob's better heat retention, it all of the sudden struck me that it would be much slicker if I eschewed gravel, cut down on the wooden-boxes size and  filled it w/ cob instead. Has anyone tried this?

I figure that I could run the system w/o a top to drive the moisture of the cob fairly rapidly to avoid moisture damage to the wood.  

Thoughts/experience much appreciated,

Steve

It's certainly possible. You would be sacrificing a bit of effectiveness because the wood conducts heat less well than cob does, but I think it wouldn't be a big problem. Keep the wood as thin as practical and you should be fine. I might consider making the box so it can be taken apart after packing the cob, so you can let it air dry after it stiffens enough to keep its shape. Then put it back together and enjoy it.

You can layer rocks in among the cob, for more density and heat transfer efficiency. That would also (provided the rocks are not too jagged) make it easier to take apart if you ever decide to move it.

Maybe a pebble-style one is the way to go, which relies more on movement of air between heated pebbles that form the mass, held in a wooden box.

Here's a link or two

https://permies.com/t/30006/pebble-style-rocket-mass-heater

https://permies.com/t/48488/Filling-Pebble-Style-Rocket-Mass

One of the dvds in the better wood heat dvd set cover pebble style.

There's been a Guy, four Years ago or so. Who bas donne one. Do a search. I seem to remember that he called that modular bench.

Matt Walker did something similar with his RMH bench rebuild/mod. But instead of wood for the box he used HardieBacker cement board, as it's called here in the US. I've also noticed that my local building supply stocks cement based "lumber" with molded in woodgrain. The stuff takes "concrete stain" really well too, which Matt has tested at typical RMH surface temperatures. Anyway, some construction photos of Matt's HardieBacker encased cob bench will be found in this thread over at Donkey's site:

http://donkey32.proboards.com/thread/1361/converting-8-6-batch

Your mass can be surrounded by just about anything . Wood, brick , stone, sheet metal, even sheet rock can all be used around your mass.  A cob bench certainly is not everybody's cup of tea. Mine is encased with regular red clay brick.  As Glen mentioned, rock in with your cob is a better heat sink than cob alone.

Thanks so much for all the excellent thoughtful advice all...what a great forum.