Oregon 46" Neapolitan Wood Fired Oven Build

[david s]

While I'm working on the slab and floor, I'm also pouring pieces of my dome in my garage. I decided to do a cast dome instead of firebrick because it was cheaper and I also thought it sounded like less work, since I was going to trim all 200 or so bricks to taper them and then laying them (and I've never laid bricks before).

Considering how much time I'm going to spend pouring segments and rigging up systems to move those segments around, I'm not so sure that its actually less work. But still cheaper

Anyway here are some photos of my form and of one of my test pieces I made with regular concrete. And also my temporary lifting setup. I lift the segments (which weigh around 120 lb) straight up, move the form out of the way, and then set them down. I just picked up a winch which should make that part much easier!

My ultimate plan is to build a wooden overhead crane with a horizonal beam and a cart with casters that can roll along that beam. And I'll mount the winch to the cart. If that works, I can stage my segments next to my oven and then lift them and set them into place with my crane. If it works, it will be pretty slick! And as you can see, I install a rebar lifting point in each segment, so when I lift the segment it is oriented correctly so I can set it right into place on the oven floor. I know its a crazy idea but it should help alot with assembling the dome.

I know I could have made each segment much smaller and easier to lift by hand but I thought bigger pieces would be better because I'd have to pour less of them. I didnt think about how I would lift them... but now with the lifting points I think it will be even easier to mortar them and set them in place. We will see...

Charles the steel reinforcing is a good idea for lifting heavy castings , but unfortunately presents problems in conjunction with refractory. Because steel is many times more thermally conductive than the refractory that surrounds it, the resulting expansion on sudden heating creates stresses on the refractory. Additionally heat and moisture both accelerate corrosion. For these reasons the recommended reinforcing for refractory is melt extract fibres (stainless steel needles). This may be overkill for your build but it might be prudent to either skip the reo and lift the castings with straps or at least reduce the diameter of the reinforcing as much as you can. I'd say 1/4" should be adequate.

On pulling apart my mobile oven after many years of pretty hard service I noticed how expanding steel reo had cracked the casting surrounding it (see pic on linked post)
#2

[CharlesPizzaiolo]

Based on SableSprings and david s 's suggestions, I'm going to remove the sand and put a skim coat of concrete down to get the floor of my slab as level as possible. I want to get it level enough that I can stack the drainage tiles, fiber board insulation, and firebricks directly on it without any need for the sand/fireclay mixture under the bricks. Mostly because I'm trying to get my firebrick flush with the concrete slab I've already poured and I don't have much height to work with. Should work though. I have a long level and will cut a 2x4 to the exact thickness of the drainage tile, insulation, and firebrick. I'll use that to make sure my skim coat is perfect. And I can always grind down any high spots.

I plan to do all this on Saturday, so I should have an update Monday!

In other news, I picked up a winch and set it up temporarily. Here's a video of me lifting a segment out of my mold. I'm wearing my steel-toed shoes because I was a little nervous This is the third segment I've poured with this mold (the first two were test pieces made from regular concrete). The first two pieces came out of the mold very easily. But this one refused to come out. I had to drive some chisels in between the mold and concrete to get it out. You can see that some of the mold is stuck to the segment. So I've got some repairs to make to my mold. The inside of the mold was painted with a high-gloss paint and I spray cooking spray before each pour. Clearly that's not good enough. So I'm going to put some plastic sheet (maybe just kitchen plastic wrap) down on the mold before I pour the next one.

[CharlesPizzaiolo]

David, I just saw your reply from yesterday. I didn't think about the difference in thermal expansion between the refractory and the rebar causing cracks! It definitely will. I only added the rebar to create a lifting point, not to add strength to the concrete. I was using 3/8" rebar. Do you think that 1/4" rebar will not cause cracking?

And would corrosion of the steel really be a problem? Ignoring the cracking and assuming that the refractory is strong enough by itself.

[david s]

Yes I realised that the steel bar is only for lifting. Maybe the reduced size down to 1/4” will be sufficient for you to get away with it. Remember that all ovens will have some cracks. I’d imagine it’ll work, if still unsure use lifting straps.

[CharlesPizzaiolo]

Here's what I accomplished on Saturday. I started by trying to do a skim coat of concrete. I got some sand topping concrete mix, which sounds like the right stuff. But I found spreading it thin very difficult. Maybe it wasn't the right material or I was doing it wrong. I was able apply some to the thickness I wanted and then gave up and went back to sand.

Then I broke up some cheap tile and started laying it. Part of the slab was too high to place the tiles and have room for insulation and floor, so I just put sand. Hopefully that will be good enough... And I drilled a few drain holes.

Next I placed the 2" fiber board. That was pretty straightforward.

Then started cutting bricks for the floor. I'm using 12" x 24" bricks in a herring bone pattern. I used a 7" diamond blade in a circular saw with my dad continuously squirting water on the blade with a squirt bottle. I had a diamond blade that was pretty worn and it only made it about 1/2" into the brick. But a fresh blade cut very nicely. The saw cant reach the last 1/4" of depth, but the pieces break apart easily with a light tap. Then I clean up the jagged edge with a concrete grinding wheel.

We got through 3 cuts. One more full day and the floor should be done. I'm pretty happy with how its looking.

One question, someone mentioned the floor bricks lifting up from the weight of the dome being placed on the edge. Is there a way to prevent that? Should I put some mortar around the perimeter of the floor, between the floor and the concrete?

[SableSprings]

I had mentioned the problem with "lift" when placing the cast dome around the perimeter. However, in our situation, the floor bricks were inside the dome perimeter with the insulation board extending a few inches further. When we placed the cast dome pieces on the insulation board perimeter, it lifted several of the cooking floor pieces out of level. In your case, you will be placing your cast dome pieces on pretty solid cooking floor bricks. I suspect the amount of contact you have along the perimeter for each section will keep the floor pieces level, so I don't believe you will have any problems just setting pieces in place.

I am a little concerned with how tight your fit is for the cooking floor. The floor pieces will expand slightly as they are heated and you do need to have a little room for the physical expansion. For most builds that lay the cooking bricks inside the dome, only a 1/4" gap or so around the inside perimeter is enough of an expansion gap. Often the gap is created by simply laying a piece of cardboard between the outer perimeter of the cooking floor bricks and the inside dome wall. In addition, you do want to have some insulation between those extended cooking bricks ends and the concrete. Remember you want to isolate the oven from "the outside world" with insulation. Any direct or near contact between your concrete base and heated oven bricks will diminish the ability of your oven to maintain its heat. I suspect the heat loss would be minimal...but at this point, I'd want to build the most efficient oven I could. Based on all the great work you've done, I suspect you will want to at least think about the consequences of that "tight fit".

[CharlesPizzaiolo]

I will pull up the bricks I've placed so far and make sure there is sufficient expansion gap. I think I will actually make a gap of about 1 inch, so I can put fiber board in between the floor and concrete. I do want this to be an efficient oven.

Thinking about placing the dome, should I mortar the dome to the floor bricks? Or should they sit on the floor?

[SableSprings]

Your dome sections should just be placed not mortared. Again the different expansions with heating/firing would possibly cause problems. If the sections simply sit on top, they can slide the little bit needed. I think giving yourself an inch of insulation around the perimeter is good.

[CharlesPizzaiolo]

The floor is finished. Had to interrupt work to buy another diamond blade and learned that the "turbo" blade is best for cutting firebrick, not the continuous blade. Left a gap just over an inch around the perimeter so I could insert scrap pieces of the fiber board insulation and have room for expansion.

I happened to have a large diamond hole bit laying around and so was able to make a perfect hole for the smoker function. Was able to use a drill press for that which made it pretty easy.

I'm excited to have completed the first step of the actual oven! Next I will lay the bricks for the door.

[Chach]

Nice to accomplish something isnt it

[CharlesPizzaiolo]

So I've got a question. I'm building a low dome. Inner diameter is 46" and the inner height is 17". I've been thinking about how the dome is meant to support itself. With a high dome the curvature of the dome is the same from the top to the base, and as far as I understand the weight of the dome gets transferred mostly into compression (and I think some shear) between bricks and the surface the dome sits on. But with a low dome, usually you have vertical walls for the first course and then transition to a curve. The result is that the weight of the upper part of the dome pushes outward on the vertical section. I've found these two photos of ovens with a similar dome (one is a barrel oven but I think the idea is the same). And they both have added metal structure to resist this outward force. There's also a drawing of my dome with some dimensions. I've been going back and forth trying to figure out if I need to do this.

I was going to go ahead and add this support because, why not just overbuild it to be safe. But now I'm thinking about the thermal expansion of the dome. When the dome heats up it's going to expand, and this metal structure would try to resist that. Of course it would not be able to, so something is going to give way.

I'd love to hear some opinions on this. Thanks!

[david s]

The thermal expansion for the temperatures we fire to is around 1% or about 5 mm/m. You could double that if it were a kiln. So, the steel bracing just needs to be firm, hence the threaded adjustment. When the oven heats it becomes tighter.

[Bwhite]

CharlesPizzaiolo What width and thickness angle iron did you use? Is the front of it flush with the cinder block or does it stick out?

[CharlesPizzaiolo]

Bwhite I cant quite remember now, I want to say 3/16 x 2 x 2. Here's a pretty good picture of it. I trimmed the cinderblocks that sit on top of the angle so that the angle sits flush with the cinderblocks. You can see me doing this in the video in post #4 on this thread.

[david s]

The conventional way of using lintel blocks/bond beams/knockouts which have a channel that can be filled with reo bar and concrete is neater, probably stronger and not subject to corrosion because the steel is not exposed.