rocket mass heater workshop*
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Rocket mass Heaters finishing?

David Texen

Joined: Mar 19, 2012
Posts: 5
I'm looking through the forms and I can't find any talk of finishing the cob heater. We have ours inside and I want to be able to sweep and mop without small amounts of cob coming off, so what would you use to make the outside hard and stable to sweeping and mopping?
Lasse Holmes

Joined: Nov 14, 2011
Posts: 20
Location: Homer, Alaska
A good hard plaster coat is what is needed. That can be as simple as sharp sand and clay slip (try a bunch of tests and find the sweet mix that has the minimum of slip to stay tough) or you can get into other plasters (lime) or ammendments. Get ahold of the Natural Plaster book by Cedar Rose Guelberth/Dan Chiras or find someone to show you.
David Texen

Joined: Mar 19, 2012
Posts: 5
thank you was just what I needed to know. will do all above till it works out right.
Daniel Truax

Joined: Jan 07, 2012
Posts: 61
I never tried it but don't some people linseed oil their cob/plaster after to waterproof it?
David Texen

Joined: Mar 19, 2012
Posts: 5
I had heard of that but wasn't sure if it made it hard enough to not flake off when sweeping and mopping.
Daniel Truax

Joined: Jan 07, 2012
Posts: 61
I am not sure cured soaked in linseed oil would make the surface harder, but I would assume it would make it tougher ie more resistant to chipping.
Kirk Mobert

Joined: Jan 07, 2011
Posts: 128
Location: Point Arena, Ca
Several coats of linseed WILL make it harder, it's what we use on earthen floors.
Seems like a bad choice for heaters. The oil is likely to do something funky in the heat.

Something I've used to lock down dusty plasters on a stove is exterior grade white glue. Thin it with water and paint on a couple-few coats. It'll golden up the color a little and give it a slightly "glazed" look. The exterior grade stuff can be wiped with a damp cloth and seems to slightly resist coffee stains..

Build it yourself, make it small, occupy it.
David Texen

Joined: Mar 19, 2012
Posts: 5
been having a lot of trouble building it think we are at Rocket mass heater Ver 1.09 keep, so tired of brake it down and start from scratch. but if anyone is intrested I have bunch of videos of what not to do at

will keep putting them up and talking about our experiences as we go along.
David Texen

Joined: Mar 19, 2012
Posts: 5
Burns have been an epic fail, only getting 100 F on top of drum. tearing down to base. Only thing i can think of is we just built it with only cob. Going to break down the cob this time and add charcoal and actually make forms . add the charcoal to cob and make actual fire brick from the forms. hope this does it getting so tired of this, don't know where I am getting the strength to do this every day. We are up to Rocket mass heater V1.09 and am just spent. one man team with the wife as foreman now so maybe you guy's can understand where I'm coming from. She hasn't helped at all on any of it yet she want to try this and that, and I'm like I tried that back in ver 1.04. Thought for the day, is living off the grid suppose to be this hard lol
Ernie Wisner

Joined: Oct 16, 2009
Posts: 788
Location: Tonasket washington
I find a good olive oil soap works pretty well. if it is a bench or bed. for the floor i treat it with paraffin wax then normal floor wax. linseed oil melts if its not yet dry and the only way around it is to use thin coats till you have the desired surface. Bee's wax melts at almost body temp while it is harder to melt paraffin or olive oil soap.

Need more info?
Ernie and Erica
Wood burning stoves, Rocket Mass Heaters, DIY,
Stove plans, Boat plans, General permiculture information, Arts and crafts, Fire science, Find it at

Consider Paul's rocket stove mass heater.
subject: Rocket mass Heaters finishing?
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