Little help with a stone oven

[flatlander88]

Just needed a few pointers on cooking with a stone oven. I went out last week to build and try one but I am pretty sure that I had too many holes in it to keep the proper heat in. I am sure that patching the holes will resolve much of my troubles but it got me thinking about more. For one, how would one know how long to pre-heat the oven? Any tricks on how to get even heat distribution? Here a few pics and a vid of what I did. Feel free to add any insight, thanks!

Guests can not see images in the messages. Please register in the forum.
Guests can not see images in the messages. Please register in the forum.



Thanks
Flatlander

[crashdive123]

Great video. Looks like a good trip. On your oven, I think you will find that filling the gaps with mud or clay will make a big difference. After heating your oven up for an hour or two I think you will find that it retains the heat longer when the gaps are filled. Not necessary, but I think you'll like the results.

As far as temps an cooking times - for me it has been trial and error, but I think you will get more consistent results (not affected by wind and external temps as much) with a sealed oven.

[Rick]

If you place flat stones upright around the inside you will increase the surface area of stone being heated. Instead of heating the edge of the stones you'll be heating the face, which will absorb more heat. The same design you have but with flat stones upright in the back and sides. The other thing you can do is reduce the vertical opening so it's not quite as large. The smaller the oven the more efficient the fire will be at heating the stone. I think you could drop the top one layer in the oven above. If you are only baking in a smaller pan like the one shown then you could drop it two layers. The final point, and I might have missed it in the video, is how long you burned your fire to preheat your oven. I would think just about any size or design could be used as long as your fire burned hot enough and long enough to heat all the stones. But in this case I think the facing stones would boost your heat absorption on the stones.

I agree on the video. You did a nice job. I liked the use of the mat cover. I've never seen that used and probably added a lot to the efficiency of the oven. The blind was pretty cool too.

[gryffynklm]

Cool video. The oven is a good idea. I agree with the above comments and yours concerning the gaps. Your house oven and even a dutch oven is closed to retain the heat. I don't know what you have available at your site. I have used stiff river clay as a mortar between rocks it works pretty well. If the clay is too wet the clay will shrink and crack a lot.

I have built temporary ovens at reenactments using a combination of dry stacked stone and packed cob. Below is a JAS Townsand Video. It may have been posted before on the forum. They show a stick basket being used as the form for the interior. This form is covered with cloth and then cob (clay sand and straw) is packed around the form. They fired it for about 24 hours as soon as the oven was finished.

The version I built last year was stacked stone covered with a cotton painters tarp. Then topped with a 2" layer of clay from the river. I fired the oven for 24 hours. and cooked in it the next day. my oven was big enough for 2 6" round loaves of bread. I should have just gone with the stick form it would have taken as much time and taking it apart would have been easier.

Remember the taller the inside the further your radiant heat. There is no need for a vent at the top or at least close it when you bake. The door is important to retain heat. Your rush mat was a good idea. Super heating rocks with direct flame can cause them to basically explode sending out fragments especially if there is too much moisture in them.

Fire time and bake time has always been different. I first fire slow to dry the rocks for the first time about an hour then do a stronger fire to heat up for baking. I fire for a few hours in the morning. While I make my dough and let it rise. Seems I start to bake after about 2 hours or so. Push the coals to the sides and back and pull some out if it seems like to much. Sweep the bottom stone scatter some corn meal in and put in the loaf. Close the door and bake until it smells real good. I take a peek when the bread crust starts to toast, I can smell it. I'm guessing about 20 min bake time maybe less. Outside temp wind and how long I preheat the oven all make a difference in bake time.


Just some thoughts on what I have done.

[hunter63]

Thanks Karl, for posting the Jas Townsend, vid....The first thing I thought of, so ya got it covered.
Even though his shows clay mud....the dimensions and design would be close to correct no matter what you use....as well as the door.

FL88 cool project.....thanks for posting.

[flatlander88]

Good info! The rocks are about at dry as they'll ever be, mainly because of our drought here. I preheated the oven with a small fire for an hour. So based on the info so far I'll add clay to the cracks, take out the top vent, bring the top of the oven down, and make the door fit better. I've actually been able to heat limestone until the point it glows red but I've also broken it from heating too fast.

I think the type of rock will work if I can get it to retain the heat given off the the rocks.

Thanks again for the info and the comments!

[gryffynklm]

If you have a good source for clay and take the route that the video does. The grass / straw they use does two things. It strengthens the clay and prevents cracking it also lighten the clay and has an Insulate quality like the air baked into fire brick.

I haven't done this, but if you build bottom up and pack clay on the inside as well, as you build up it may help retain the heat better by the increase in thermal mass. If you did that the outside layer might not have to be as thick. Ether way the goal is to plug the gaps preventing the heat from escaping. It is the stored heat that does the baking. More mass longer heat radiance.

Lime stone will often fracture under enough direct flame contact. I think it is caused by uneven extreme red heat and duration. I have fired a lot of limestone to a red heat. Clay will insulate the lime stone from that fracturing heat. Besides you do not want to bake in a red glowing oven, you will probably never get that hot.

[LowKey]

Is the idea to go full native with at-hand materials? No firebrick for the floor?
You can also create a heat sink by building on a concrete/vermiculite pad. Sand might also work.

The only stone oven I've used (it was a class in hearth cooking), you fired the oven to warm up the stone mass. Then you swept out all of the ash and embers. Then you mopped it down to make sure you got all the ash out so not to get in the food. The heat from the stones does the cooking, not a banked fire. The floor was smooth brick with leveled joints so you could peel a loaf of bread in there if you wanted, though we cooked bread in a stoneware crock.

You might want to add mass to your stone oven to help hold that heat. Maybe seal this layer and add another. Do a little research on the actual shape of dome cooking ovens. As Gryff said, they are usually lower. If you're really into it, the book called Bread Builders shows you plans, but there are free ones out there on the web (try Pompeii Oven plans). Also like Gryff said, heating the rocks too fast will cause them to splinter. It isn't water that does it. It's thermal inconsistency. Portions of the rock heat faster than other portions and can cause pieces to spall off. It's actually used as a rock carving method.

Looks like fun though. You were able to cook with it first try so that is what it's all about.

[flatlander88]

Thanks again guys! I am aware of the thermal cracking (heating too fast) but after reading everything you all wrote, I think I know what I have to change.

Lowkey - I am not quite as interested on 100% native materials but I think I would be awesome. I am willing for any tips to make it work. Limestone (at least in my small area) is all the rock we have, so I was just playing with what was available.

flatlander

[gryffynklm]

I will second LowKey on those sources.