Stone fireplace in a cob

I'm currently learning rock shaping and stacking to start the base knowledge to build a cob with stone fireplace later.

To start I'll dry stack a bit

Then I'd like to build an outdoor stone oven.  Mortar mix? 1 portland cement, 2 sand, 2 clay?  Or other recommended mix?  

Then, I'll be ready for the cob.  Different mix for a rock foundation?  

Thanks for any tips!  I've read so many different mortar mixes that my head is spinning now!

I don't have any experience building one though I remembered this thread that might help:

https://www.instructables.com/Stone-Oven-How-to-Build-Use-Primitive-Cooking-Tech/

From:

https://permies.com/t/215180/Stone-oven

Hi John;
I used a clay mortar on my outdoor brick oven.
3 scoops of sharp medium sand and one scoop of fireclay.
It makes a beautiful pale white mortar.
I do have a roof over it so I'm not sure how it would hold up exposed to rain and wind.
Matt Walker uses the same mix on outdoor stoves and he says that a springtime touchup of mortar with your finger works well for him.

thomas rubino wrote:Hi John;
I used a clay mortar on my outdoor brick oven.
3 scoops of sharp medium sand and one scoop of fireclay.
It makes a beautiful pale white mortar.
I do have a roof over it so I'm not sure how it would hold up exposed to rain and wind.
Matt Walker uses the same mix on outdoor stoves and he says that a springtime touchup of mortar with your finger works well for him.

I'm having trouble finding fire clay that's not $100 a bag except one spot in Canada.  Any recommendations?

Hi John;
Locate a masonry supply house, any larger city near you should have one.
I pay $8-$14 for a #50 sack in Missoula or Spokane.
In Canada, it is apparently hard to find.
I can ship you #20 for $35 if you can not find it locally.

thomas rubino wrote:Hi John;
Locate a masonry supply house, any larger city near you should have one.
I pay $8-$14 for a #50 sack in Missoula or Spokane.
In Canada, it is apparently hard to find.
I can ship you #20 for $35 if you can not find it locally.

Evidently a huge refinery is 40 minutes away! I'll be contacting them after the holidays to either find some vendors or buy bulk direct from them.  Euclids Pottery in canada actually gave me their info!  


I'll start playing around with mortar mixes.   1pt portland cement, 2pt sand, 2pt clay to begin and start tweaking from there.   maybe add some lime and see how it changes.   I'd love to morph this into a mass heater somehow

Having worked in refineries many times, I suspect that you will find,
Firebricks both heavy and insulated, full size and splits.
Refractory cement, ceramic blanket and ceramic boards.
What I doubt you will find is fireclay.
A masonry supply would carry fireclay for fireplace builders.

thomas rubino wrote:Having worked in refineries many times, I suspect that you will find,
Firebricks both heavy and insulated, full size and splits.
Refractory cement, ceramic blanket and ceramic boards.
What I doubt you will find is fireclay.
A masonry supply would carry fireclay for fireplace builders.

I talked with someone that wasn't a sales agent earlier there about it, they have a lot of fireclay products.  Missouri is evidently the place for fireclay.  Christy minerals is the place

Would a lime mortar work well?

John C Daley wrote:Would a lime mortar work well?

That could be used as part of the mix but any refractory or high temp mortar needs fire clay as well.  

Found some in Saint Louis that is being shipped for a pretty low price, so Im good!   The local refinery requires a pallet to buy, which Im not quite there yet