36" build in coastal VA

[nlinva]

The Thermo1200 stuff is reasonably even, thickness-wise, but there are some thinner sections, and one of the boards was noticeably thinner than the others, by a couple of mm. Fortunately I had spares, so I managed to get them cut and shaped well enough. Some unevenness remained, but that was solvable with some sand to create a level surface for the floor bricks.

I didn't much like the idea of having bricks resting right on the edge of the insulation, so I cut it to extend 4" beyond the oven walls. I plan to have 4" of the superwool insulation around the dome, so that should come right to the edge of the Thermo1200 boards.

[nlinva]

After going back and forth about it repeatedly, in the end I did decide to make my floor a bit thicker than a single flat brick. I am placing a base layer of 1.25" firebricks, with my 2.125" bricks on top of that.

The dome will be built on the base layer but around the main oven floor. One advantage of this set-up is that I am able to correct almost all of the unevenness of the insulating board with a clay-sand mixture underneath the base layer, so main oven floor requires almost no additional leveling.

The overall oven floor slopes ever so slightly up towards the front right corner, but no no more than a few mm. across the entire reach of the oven, so I'm not worried.

As you can see in the pics, I made a small mistake in my initial planning for the base layer, and had to re-do the front left and right bricks to support the entry arch.

[nlinva]

Today I mocked up my entry arch. I'm going with an 18" x 11" opening, with the upper part being a half circle. The planned dome height is about 17.5" (the pivot point of my IT sits about half an inch below floor level), making the ratio of opening height to dome height almost exactly 0.63.

Happily, the arch shape works out just about perfectly with no need to shave down any bricks, and a single TDC brick at the top. As you can see on the picture, my arch form is not quite a perfect half circle (poor jigsawing on my part); I'm going to improve the shape a bit before doing the actual mortaring. I am also going to cut off the bottom half inch or so off the form, so I can raise it up on small wedges, and make it easier to remove once everything is set.

I am thinking of adding a small chamfer to the front of the arch all around, to reduce risk of chipping if/when I hit it putting things into the oven.

[nlinva]

Tomorrow I hope to put in the first two courses. I have enough of the thin 1.25" firebricks left over to make a first course around the oven floor. That will raise the second course above the oven floor level by about 1.4", which means there is no seam right at the level of the oven floor (something I read as a suggestion on someone else's build).

I have a thin strip of ram board around the oven floor to allow for expansion, with the idea that it will burn away in the first few fires. Is ram board thick enough for that purpose (it's about 1.2mm), or should I use corrugated cardboard instead?

[Toiletman]

Welcome back to the forum nlinva, glad to see another build in progress!
I can't really comment on the ram board, as I have built my dome directly on the floor. I would expect the amount of expansion to be similar for all bricks, due to the evening out of the temperature gradients, but I might be wrong. I'll let others chip in for a better answer.

[rsandler]

I used a mix of cardboard thicknesses on my current oven (whatever I could quickly lay my hands on), some of which were closer to 1.2mm; probably fine.

[nlinva]

Since the front part of my insulation is still exposed, I thought I'd add a pic of the uneven thickness. This is the front left of my insulation base. The pieces on top are laying on the same block of insulation, so any difference is not due to unevenness of the slab. It's a little hard to see, but you can see the protruding edge along the top; here probably a 2mm. difference in thickness between the left-most piece and the one next to it.

[nlinva]

Yesterday I did the first mortaring, using the 3:1:1:1 homebrew formula.

It's definitely a learning process. The first batch of mortar was a little too wet; some bricks were a little too wet, some a little too dry, etc. But I think I'm getting the hang of it (fingers crossed!). Despite the heat (around 90F), the mortar remained quite workable for as long as I needed -- possibly because it's so humid here right now. It probably helped that I used chilled water to mix it, as recommended in several places on the forum.

I put in the first two courses, one thin, one normal-size, plus the inner arch. I ended up having to taper the bricks on either side of the TDC brick a little bit, but other than that everything seems to have gone smoothly. Today I removed the form (very glad I had raised it on some shims, because otherwise it would've definitely been stuck!).

I had a little mortar left over, so I put in the first 2 bricks of the next course, which will be the first to curve inwards. I'm thinking I'll need to build a jig to standardize the taper/bezel. I thought I might be able to do it by eyeballing, but I think a jig of some sort will be more efficient.

[nlinva]

A quick question about keeping the mortar damp: I covered the mortared bricks in wet towels yesterday evening, and covered the whole thing with a tarp. I re-wet the towels this morning. Do I need to keep doing this, or after, say 24 hours, can I just leave things to air dry slowly?

[david s]

Anything made with Portland cement can have its strength enhanced by holding in the moisture . It’s called damp curing. Generally a week is considered reasonable. Brickies building houses or walls never bother because it’s not practical. To achieve maximum strength 28 days is recommended. Bricks should be moist, not wet. A film of water on the brick surface can interfere with the bond. Again brickies never bother to even get their bricks moist, however if you are after the maximum strength it is worthwhile. Also working in the late afternoon reduces afternoon sun from drying things out too raidly, having the night toassist moisture retention. In the hot months I always have to avoid casting jobs in the morning that contain portland, for this reason, Otherwise I run the risk of getting shrinkage cracking.

https://advanceroofingllc.com/blogs/...nd-durability/


Wedges should be placed under the arch formwork, so when they are removed it can be dropped slightly. Otherwise the arch can be damaged.

Thermal expansion at pizza temperature results in around 3mm linear expansion. This would mean about 1.5 mm at the perimeter. In practice if the floor bricks are laid loose it is sufficient to relieve this expansion stress. The gap you have planned should be fine.

[rsandler]

To add on to David's comment, you will likely find that draping the bricks in a wet towel is handy anyway, as you start building the dome, as otherwise the bricks are more prone to sucking the moisture out of the mortar for the successive courses, preventing a good bond. If you're going to do that (recommended), and you've got enough towels around, may as well keep the mortar damp as well.

(That said, I never put much effort into properly damp curing the mortar on my ovens, and my ovens held up fine. YMMV).

[rasorface]

Go with the CalSil L it’s better for insulation. Foamglass isn’t needed if you’ve got good drainage and tiles; 2 layers of CalSil should do the trick.

[nlinva]

I've built my brick cutting jig. Looking around on the forum, I came across cbailey 's version, which I used as a starting point. I liked the idea of making it from hard plastic rather than wood (less affected by water), and I also wanted to keep it as thin as possible, so that a brick can rest on it, even at an angle, and I still have enough clearance for the saw. My saw can cut through about 3.5", so with my brick thickness of about 2.25" and some added height from having the brick at an angle, I figured I had at most 1" total to work with. This jig is about 3/4".

I opted to hinge two cutting boards together with the thinnest & smallest hinge I could find. The cutting boards are thin enough that the hinge screws stick through a little. I sawed off the tips, and the remaining slight protrusion actually helps keep the brick from sliding.

A small piece of 3/4" aluminium angle allows me to control the taper, with a C clamp fixing it in place. The C clamp obviously protrudes a bit below the top cutting board; this would potentially constrain how small an angle I can do for the bevel; fortunately, cutting away the bottom cutting board mostly takes care of this. I think I can get down to the angle I need (if not, I can always raise the whole jig on another flat piece of plywood).

Finally, two bolts allow for the top cutting board to rotate up for the bevel, by an amount controllable by pairs of nuts that clamp the top cutting board between them.

As you can see on the second pic, the cutting boards have raised edges; this conveniently allows the heads of the 3 bolts (2 for the bevel adjustment, one as the pivot for the taper adjustment) to not take up any extra space; this, again, facilitates making very small angles for the bevel cut.

[Toiletman]

Yesterday I did the first mortaring, using the 3:1:1:1 homebrew formula.

It's definitely a learning process. The first batch of mortar was a little too wet; some bricks were a little too wet, some a little too dry, etc. But I think I'm getting the hang of it (fingers crossed!). Despite the heat (around 90F), the mortar remained quite workable for as long as I needed -- possibly because it's so humid here right now. It probably helped that I used chilled water to mix it, as recommended in several places on the forum.

I put in the first two courses, one thin, one normal-size, plus the inner arch. I ended up having to taper the bricks on either side of the TDC brick a little bit, but other than that everything seems to have gone smoothly. Today I removed the form (very glad I had raised it on some shims, because otherwise it would've definitely been stuck!).

I had a little mortar left over, so I put in the first 2 bricks of the next course, which will be the first to curve inwards. I'm thinking I'll need to build a jig to standardize the taper/bezel. I thought I might be able to do it by eyeballing, but I think a jig of some sort will be more efficient.

Wow, ambitious to start with the arch! But great progress!

For my arch I opted to cut each stone to width towards the dome while laying the courses such that the arch bricks would also interlock with the dome courses for added structural strength. But I guess you are past that station now. Don't think it really matters.

[nlinva]

Toiletman Yes, looking at your pictures I see how interlocking in that way can make sense. It may be easier to do when the entry walls go up straight for the first few courses, as in your build.

Ironically, I had decided that interlocking with the dome courses might weaken the arch's own structural strength, but I think you're right that it would strengthen the connection between the arch and the rest of the dome. In the end it's probably "lood om oud ijzer" :-)