I'm in the process of building a wood fired oven within a dry-stone structure. I've been at this at least since September 2010, when I started brainstorming. Since I started so long ago, I have already come quite far, and am currently working on the oven itself. You may notice that I'm not a professional mason in the sense that I don't make my money doing this. I'm actually an attorney, but I take stone work very seriously. I hope no one will hold that against me!
That said, I started out doing dry stone masonry in 2008. I've done quite a few free standing walls and retaining walls, including some corners, steps, an arch, etc... However my wife wasn't very impressed, considering the time I was spending outside. So I set off to build a brick oven housed in a dry stone structure, meaning there would be no mortar to set the stones in. I realized that in order to do this, I would invariably have to find a gigantic capstone to cap everything together at the end, or the oven would get wet and I wouldn't get all the stones tied together properly. So I went in search of a stone that might work, so that I could design an oven and structure underneath it. I found one on a creek bank which was already almost rectangular. After I split a section off, it was 6'x4'x9" thick, and more importantly, it was accessible by the creek in only 2 feet of water, meaning I could drive a tractor up the creek to get it. So that's what I did first. I built a sled to lay the rock on, went down to the creek and jacked it up and slid the sled underneath and towed it out of there. Here is an album of the pictures: http://imgur.com/a/bsS2O
Here are two pics of the stone, for those who don't wish to visit an outside site.
I may be a bit slow on updating, but that's only because I'll be uploading and arranging pics as I go. The next post will be about how I chose a spot in the yard and dug and set the foundation.
If you will have external walls, just fill the space with loose perlite or vermiculite. If not you can use a ratio of 1 part portland up to 12 parts perlite/vermiculite.
Awesome. I'm going to build stone up around the oven, so I'll fill the space with perlite or vermiculite. Perhaps I can atone for sin in failing to insulate the slab by insulating the walls and vault well.
And btw, I do have the ambition to bake large quantities of bread. That's why I did this style.
But like I said, I just rent this place and I'm going to build a house at some point and I'll build another oven, so all suggestions will receive careful consideration.
I'm impressed with your stone skills. Yes the oven dynamics are not perfect, but it will cook pizza. Most of the world has cooked bread in uninsulated stone/mud/brick ovens for thousands of years. Keep the pics coming.:thumbsup:
Yep, the difference is one of efficiency, not of efficacy. My oven, for example, requires that I burn about 2-4 cubic foot of wood, roughly 6-8 sticks of split oak (plus kindling and newspaper to get it going). That will provide a 800 degree hearth, 900 degree walls, and will have enough retained heat to cook 6-10 pizzas without a recharge of the hearth. The oven will not return to ambient temps for 4 or 5 days, and is usable for the entire time.
An oven with the mass of yours plus the lack of hearth insulation will probably require 10 to 12 cubic feet of wood to reach the same temps, and will not hold those temps without additional firings. The huge thermal mass will draw heat from the oven surface instead of recharging it unless you are willing to heat the entire contiguous mass, which means 5 or 8 hours of firing as opposed to the hour or so that an efficiently designed oven requires.
I could provide the math, but would it matter? Your oven is what it is, and I am not really speaking to your oven, I am speaking to those who may read this thread and build their own.
Well there is little need to estimate since I'll have thermocouples in the hearth and vault. I'll post heating times and the wood necessary when I get that far.
Thats a cool feature but a thermocouple only reads surface temps and what is being said here is that even if your temp reads 800 after an hour or two, if you dont maintain the fire in your oven long enough the heat with be rapidly lost because of the thermal mass.
BTW, nice arch form. I did the same thing last year on a dry stone wall...they work great.
oh yeah....I'm only doing the earth oven because I probably not have time to built the permanent one before the serious heat kicks in.....The "Taj"(those are your words my friend) is still on...just delayed.
oh yeah....I'm only doing the earth oven because I probably not have time to built it before the serious heat kicks in.....The "Taj"(those are your words my friend) is still on...just delayed.
Loom? You mean loam maybe? This is heavy clay it's sitting on. I'm not saying it won't move during settling, because it seems impossible to me that it could not over time. However I did ask a DSC and DSWA certified master mason and he said as long as got under the initial spongey topsoil, I'd be fine. Might take decades to see if he was right.
Tscarborough, or anyone else for that matter, any thoughts on the ideal dimensions for the 'inner' hearth for a vaulted bake oven? Specifically one for 'personal' use... (honest officer, I'm just holding it for a friend...) If I recall correctly, your own oven is something like 24 x 32 ish... do you find that large enough?
I cant really say if 24"x32"is large enough but IMO it sounds a bit small. I have only built domed ovens 36"- 38" in diameter. My next one will be around 42".
It really boils down to how you plan to use the oven. If you entertain a lot or plan to do some baking then a larger oven might be the way to go. If not, then a smaller oven is easier to manage.
I dont know if you caught this thread yet so I'll post it to avoid repeating some of the same info.
By combining last weekend, two nights this past week and this morning, I was able to finish the brick portion of the oven. These were my first brick arches, and it was exciting to build. I ended up with an entrance about 62% the height of the vault. Now I need to think about insulating it on top. What is the perfect mix? Perlite, refractory mortar and regular concrete?
The mix I have been using is 5:1 (vermiculite/portland cement) and is recommended by FB...but it dont clad the ovens with this mix..I use it under the floor. I use loose insulation and ceramic blankets or rockite insulation for the oven itself. But the ratio works great for insulating and you can use perlite too if you want. No need to use refractory for the insulating concrete.
Since you are constructing a dry stone structure and cant use loose insulation, have you considered getting a ceramic blanket to cover the vault before you add the insulating concrete layer? A 1" blanket will greatly increase your insulation value without added bulk.... use it in tandem with a 3"4" layer of insulating concrete. In fact you could do a leaner mix for the cladding if you want like 6-8:1. Mix it by hand and if you get vermiculite, try not to bust it up to much.
I feel the need to stress this again. Don't add any more thermal mass to your oven!
Too much thermal mass = bad Lots of insulation = good
So I could just do a 5-8/1 vermiculite/portland cement mix for 3-4" over the top? I do realize I want to keep the heatable mass in the vault very low if possible. I've never heard of using a ceramic blanket. Any idea how much would one cost big enough to cover this oven?
Ceramic blanket=expensive but efficient, and totally ineffective when wet (which applies to any insulation). It is imperative that it be water tight, which will be hard with drystacked walls. I would recommend blankets with poly over them, weeped to remove the inevitable water. Looks good, other than the massive amount of thermal mass you will have to heat.
Heat always flows downhill, so until the entire mass is at your desired temp, the mass will suck heat away from the interior of the oven, and in my experience, it is challenging enough to heat saturate 3-4 inches of mass, much less the 6 or 8 you appear to have.
If I'm going to have trouble heating it, then I want to insulate as well as possible going forward. So I went ahead and bought some ceramic blanket for the oven. I'll wrap everything, even the sides that have cladding already. So you're saying I should wrap the oven then coat the blanketing with some type of polymer? What sort? And then drill weep holes, that's easy enough.
I will definitely cover the blanket in perlite/portland cement cladding. As for loose fill, I could put in a ton above since I'm going to do a barrel vault in dry-stone. In any case, after I do the vault, I'm going to put a huge stone on top that will block out moisture. The walls around the oven will be 18-22" thick, so I do think it will be protected from moisture eventually.
That said, one serious problem is that it will take me a long time to finish the vault and place the giant stone on top to tie it all together, and during that time, rain will be coming down on my cladding, which if I'm not mistaken, at a 6/1 perlite/portland cement mix, will just crumble away, correct? Is it possible to seal the cladding well enough that I can work without a tarp?
The blankets should be fine by themselves, because I truly do not think you will ever get the whole mass heat soaked. 6 mil poly, 2 layers over the blanket and flashed through the base course of the dry stacked enclosure with weeps per standard practice will keep the water off the blankets. I would not put perlcrete/vermicrete over the top, it will only suck up water. The blankets are enough.
For the first time,I don't really agree with you Tscar. I wouldn't put plastic over the blanket at all.. even though it has the weep holes. I'm not saying it couldn't work, but I think the plastic would trap moisture that would have otherwise evaporated if the blanket was covered with a verm/perl & concrete cladding. Unless the plastic is full of holes...but then you are back to the original problem. If it was me, I would clad the blankets with the layer of insulating concrete then apply a layer of modified cement for protection against water intrusion...which it will especially if he puts a stone slab over the top of everything. At least this way the dome is still a breathable masonry structure.
I do agree that loose fill is probably not the way to go on this oven...like I said earlier, it would be a sponge when it gets wet.
But hey....its not my oven. I am just arm chair quarter backing here.:laughing:
Also, I would recommend that you begin curing the oven before you go further. Start with kindling fires and work your way up to, "Now that's a FIRE, Gus". Your goal is to smoke out the moisture in the mortar and the bricks and concrete, so when not being fired you should keep the whole thing tarped.
After you burn 5 or 10 curing fires, burn one for about 4-6 hours, and if you can still touch the outside of the oven walls then you can decide whether to tear it down and start over or not.
The only problem with that is that it will compress the blankets, thus reducing their effectiveness. You may do better with loose fill and not wrap the oven with plastic, but the underside of the roof and the walls like I did, plus weep it.
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