36" build in coastal VA

[david s]

Dome clearing achieved!

I've been doing my drying fires at gradually increasing temps, and today the top of the dome finally cleared. Exciting to see that happen!



I didn't want to push the fire hot enough to clear everything, but this feels like a good moment to pause the drying fires and put on the vermicrete outer covering on top of the blankets. Nothing on the outside of the oven is getting at all warm, so I feel pretty comfortable putting the vermicrete on and once it's basically dry (after about a week, I guess) continuing with fires and using the oven. Am I right to assume that vermicrete does not need wet-curing since it contains so much excess water to begin with?

Yes that's correct and you are not trying to achieve a really strong layer anyway.

[nlinva]

Dome clearing achieved!

I've been doing my drying fires at gradually increasing temps, and today the top of the dome finally cleared. Exciting to see that happen!



I didn't want to push the fire hot enough to clear everything, but this feels like a good moment to pause the drying fires and put on the vermicrete outer covering on top of the blankets. Nothing on the outside of the oven is getting at all warm, so I feel pretty comfortable putting the vermicrete on and once it's basically dry (after about a week, I guess) continuing with fires and using the oven. Am I right to assume that vermicrete does not need wet-curing since it contains so much excess water to begin with?

[nlinva]

Yes, I guess I'll give it a shot.

I think for the rollers at the bottom I'm going to use stainless steel square U bolts. Or, as one Chinese seller has it on the big river site: "u blots" :-)

[david s]

Best way is to build it and try it out.
There’s a reason oven manufacturers do not offer insulated doors. Many of the suitable materials are either not food safe, not strong enough, too heavy or too conductive. I’ve settled on a one inch reinforced vermicrete panel that I cast in two layers, which is attached to a 1” quality timber (Quilla) facing with 5/16” (thin to reduce conductive heat transfer) stainless bolts and washers. The facing and insulating panel are separated by beads of high temp silicone to reduce conduction. While the door is light enough to use one handed and the insulating panel sufficient to hold back baking and roasting temperatures for a few hours, it cannot be used to hold back pizza temperatures overnight in an effort to use the oven to roast or bake the next morning.

[nlinva]

Current door thoughts:

I can get some vermiculite board, and cut it to shape. I could make it 2 layers, plus a mostly "empty" middle layer. The layer facing the fire would have the high-temp silicone on the face along the outer edges to ensure a good seal, as well as on the bottom, for a bottom seal. The mostly empty layer would provide some additional insulation (like a double window: the air inside would not circulate), plus it would provide space for the endpoints of bolts connecting the insulating material to the outside front of the door, which would be wood. That way the bolts would not be directly exposed to the fire in the oven, and conduct less heat through to the wood.

In case that's unclear, maybe this quick-and-dirty sketch helps (VB stands for vermiculite board in the sketch)



The 3 layers of vermiculite board could be attached together with a special "board adhesive" sold by Vitcas which is supposed to be for precisely this kind of thing. The layer that faces out would, then, be connected to the wood face of the door with both a bead of the high-temp silicone and 4 bolts, which would connect into 2 handles. I think I'd want to put silicone washers between the wood and the layer of vermiculite so that the bolts don't bend the board towards the wood.

The vermiculite board is 1.25" thick, so 3 layers would add up to 3.75", plus maybe about an inch for the wood front. The weight of the vermiculite would be about 16.5lbs, plus a couple more pounds for wood and bolts, so I imagine it'd end up around 20lbs. Heavy but doable. One question is whether the board adhesive is strong enough to hold the layers together (I worry about the shear resistance of the connection).

In addition, I hope to put rollers on the wood face, along the bottom right near the floor, so I can tilt the door back towards the entrance and roll it in and out rather than trying to lift it smoothly without touching any of the sides.

The big river store has all kinds of steel rollers that would do nicely, but they all seem to have galvanized end caps. Since I'm not interested in being poisoned by zinc, a question is whether the temperature on the outside of this door might get high enough to be a problem. Perhaps a better solution would be to simply use a couple of cylindrical stainless steel spacers on a bolt, and then mount the bolt along the bottom of the door. Not entirely sure how that would be done, but maybe someone here has a good idea?

Anyway, does this sound like a feasible idea? I think for the short run I may still build something simpler with leftover blanket and maybe a thin sheet of steel from the big orange store, but as a longer-term solution, this feels like it might work.

[nlinva]

Forgot to mention that the chimney draws very nicely, so that I see very satisfying smoke patterns that stay in the top half of the dome, flow straight into the flue & don't make it out the front of the oven.

[nlinva]

Yes, that was basically my thinking. I have a 2" reveal around the inner arch, so I should have enough play to be able to do that.

Update on the drying fires: I think I'm being sufficiently careful (perhaps even too careful) about not going too fast. Day 1 I tried with just a few half-burned out briquettes that were left over from grilling, and that raised the dome's temperature maybe up to 100F -- a temperature not far over what the dome has already seen as the outside temperature this past August.

Yesterday (day 2), the dome got up to close to 250F for a very brief moment, but hovered closer to 200F for maybe an hour.

Today I've got it at between 250F and 300F for probably close to 2 hours. Tomorrow I may get a little more ambitious and get a larger fire I can spread more widely around. The fires today and yesterday just sat on a very small part of the oven floor, and their heat did not extend out very much laterally. The bottom of the dome all around was maybe close to 100F only. The hottest temps I've measured, by far, are right after moving the fire to a new location, on the bricks where it was sitting (500-600F), but again that is very localized.

[Giovanni Rossi]

I didn't use the Permatex on the bottom. I put a continuous bead up one side, around to top arc and down the other side. The door sits tight on the floor. I suppose you could try it. My door requires the top be tilted toward the dome to fit under the outer arch. I would probably be scraping a bottom bead on the floor as I manipulated the door. If you're able to set your door bottom first and rock it in place, that could be a winner.

[nlinva]

Ooh, I like the idea of using the Permatex as a way to ensure a good fit. And I have enough left in the tube to do that, which seems like a great use for it.

From browsing around online it looks like vermiculite board might abrade relatively easily, but otherwise its properties look promising. I'm thinking it's worth a shot, especially if I also put some Permatex on the bottom, which is where I figure abrasion might be most likely, when moving the door in and out.

[Giovanni Rossi]

Door questions:

In either case, I'm planning to use nomex gasket tape where the door presses up against the outside of the inner arch, as well as probably along the bottom, to get a reasonably good seal.

I'm working on a new insulated insert to fit behind my door. Going through some of the same decision points that you are. I use the insert plus the door to retain heat when not actively cooking. Otherwise, I'm just using the handled door. I'm experimenting with materials to decrease heat loss around the door.

I had investigated Nomex as a wrap around the insert and decided to walk away based on possible shedding of the material. I didn't want to risk the fibers getting in my food. You may want to do a little more research on the material.

My door is thick steel. I tried a wood stove door gasket, but it easily abraded after two firings with normal use. When I read about others using the red Permatex as a heat break, I removed the gasket (the adhesive was a bear to get off) and ran a bead of the Permatex in its place. Only one firing since, but pretty happy with it. It held in place and is pliable enough to make a nice fit against the inner arch. I haven't seen any pieces shedding - the bright color would make it easy to see.

[nlinva]

Door questions:

I was initially planning on getting a thin sheet of stainless, cutting and bending it around 3-4" of left-over superwool, and attaching, with cement and bolts, to a wood front. This is pretty straightforward, but I worry a bit about the stainless warping out of shape and therefore not closing smoothly against the front of the oven.

As an alternative, I'm now considering simply getting vermiculite board and attaching that to a wood front. This would require buying vermiculite board. But since I don't have a nice sheet of stainless lying around, I'd have to purchase that in the other case, and that cost seems comparable to getting 2 1.25" pieces of vermiculite board (they come as a 2-pack).

The board would need to be cut to shape, and one question I have is whether I would end up with a very brittle/powdery edge where I make the cuts. Would it be possible to "seal" that with the high-temp Permatex silicone, for example?

Another question is whether it is feasible to cement the two pieces of board together to get 2.5" of insulation. I don't really know what the vermiculite board is like to handle and work with, so I'm a bit uncertain about whether what I'm imagining is a feasible approach.

In either case, I'm planning to use nomex gasket tape where the door presses up against the outside of the inner arch, as well as probably along the bottom, to get a reasonably good seal.

[nlinva]

That's a good idea. I do have an old halogen work light lying around; might need to get a bulb for it, but worth a try.

I do not yet have a door, and am realizing that should maybe move up on the to-do list. But for now I can just use the form instead, as you suggest.

[rsandler]

If you can lay hands on one, a big halogen light can be a good starter for drying out the oven, prior to trying charcoal or wood. If you close off the oven mouth (perhaps using your form if you don't have an insulated door ready, you can raise the temperature a surprising amount, with no risk of heating too fast. I managed to get my second oven to over 240F with a light in there for 2 days, and this helped remove a lot of the moisture before I started fires (just as well, since I had a heck of a time keeping the fire temp where I wanted it )

[nlinva]

Toiletman -- fun to have a koolmees in there; a pimpelmees would be even better, because those are always just a bit more special (at least in my memory). I've been keeping my inner arch form close to the dome entry at night, to prevent any critters from really deciding to hang out, but I fully expect to find a small frog in there some morning -- they seem to get in everywhere.

Today I tried to have my first fire, but I realized that my infrared thermometer was without a battery, and my the time I got a new battery, the charcoal pieces I was planning to use (and which were waiting on the grill) had mostly finished burning out. I transferred them to the oven, but they boosted the oven temp only by a few degrees. I'm going to try an actual fire tomorrow. I must say that the oven floor looked quite large with a few forlorn pieces of charcoal in the center; it's going to take more than that to get any real temps going.

[Toiletman]

After some cleaning, and adding silicone caulk to the expansion joint between the vent arch and the front landing, it was time to start on the insulation.

In the planning stages, I had aimed for 4" of Superwool; I calculated this required 3 boxes worth. Those initial calculation may have been for a 39" oven -- I'm not sure. With a 36" oven, I had calculated that those 3 boxes would suffice for 5", so that's what I set out to do.

I used all the off-cuts for the top and edges of each layer, which helped prevent wastage. As it stands now, I have 3" inslulation (mostly superwool, but some CalSil) throughout, and 5" for the dome. I added an extra inch (making it 6" thee) for the top of the dome, since my dome height is close to 1" below where a true hemisphere would be.

On the whole, I found the Superwool pretty comfortable to build with. it wasn't too hard to keep the shape of the dome pretty smooth, and to fill in gaps with off-cuts.

I think it is now time to start the drying fires. Kind of nervous about it, to be honest, but will track down my infrared thermometer and start the first fire tomorrow.

I also added a bit of insulation to the top of the chimney transition. The plan here is to add a bit of vermicrete to make it slope down just a bit from the chimney pipe to the edges, with the collar resting on the vermicrete. I plan to put a high-temp silicone gasket between the collar and the chimney pipe. The question is what I should do between the collar and the vermicrete/render it rests on. I can integrate it into that, or I can rest it loosely on top. The advantage of the latter is that this could serve a purpose comparable to the breather cap on the dome. The disadvantage is that it is theoretically possible some tiny critters might creep in and make a home. What do people think?

Great progress man, and the decorative arch and brick bottom row makes it already look a lot more 'mature'. Really jealous that you are already this far, and close to firing it! I also just did the kit and have now covered the oven for winter.

With regards to critters: I wouldn't worry too much: I think they'll get in anyway, a spider has already made a home of the pizza-oven, and this morning I even saw a 'koolmees' make its round into the oven to see if there were any spiders or other bugs to eat....