Build started in Mountain Top NSW

[SableSprings]

I mortared my outer arch down since I did not expect those bricks to experience any major expansion/contraction from heat swings. As David S has noted, the heat break that some install is more about providing an expansion joint than making a significant impact on heat loss. I'm a little unclear by your post if you mean the primary arch (closest to the oven-since that's where I see the insulating bricks) or the actual outer arch (farthest away from the oven).

My advice for you is to look at your oven in terms of expansion/contraction. The dome usually is 1) just outside the cooking floor (so both have "room to grow") or 2) the dome is on top of the cooking floor so shifting of the dome and cooking floor doesn't affect structural integrity. In reality, the curing of the oven will create it's own expansion joints as needed...the cracks . But because of the dome dynamic engineering strength, these cracks rarely (if ever) cause a structural failure. In fact, many old time bakers relied on the appearance and changes in their oven's cracks to judge the oven's readiness. Mortar down as you feel appropriate...you've developed good instincts during your build and review of the forum...relax

[Gretsch]

To clarify, theres three arches apart from the inner most. Ill be leaving a 15mm gap between the dome (and its arch) and assemble the three arches (inner one, chimney arch and decorative house brick outer arch). The first two will be sitting on the insulation bricks. I know they wont get really hot but because its standing on its own I just feel I need to secure it down.

I've seen others use a piece of metal between the dome and outer floor as a heat break, I can't imagine it would stop heat flow. As you mentioned, the heat break is more about expansion joints rather than heat loss so that shoots my theory down.

I'm mortaring a row of house bricks around the insulation bricks to stop them possibly moving and I intend on mortaring the outer decorative arch bricks on this outer most row of house bricks. There is one concern and that's the house brick row is part of the of the chimney, although it's the outer most row I don't think it's going to get a lot of heat on it.

So I havent used any mortar or glue on the insulation bricks and am hesitant to do it. Maybe just a layer of fire clay and sand will suffice. Hope that makes sense, the picture shows the layout I'm considering.

Maybe I'm procrastinating

[SableSprings]

Your layout looks good and your plan seems pretty sound to me. My outer chimney arch and outside smoke chamber section are built with house brick and I've not had any issues...so far

Since you've corralled the insulation bricks, shifting should not be a problem. A layer of fire clay and builders sand to level the house or fire bricks will be all you need...they won't be going anywhere. I strongly support procrastination as it allows you to fully appreciate adult beverages...

[Gretsch]

I strongly support procrastination as it allows you to fully appreciate adult beverages...

That’s my excuse and I’m sticking to it
Cheers Mike

[Gretsch]

Finished the entry arch today, didn't take too long, I did it in 2 stages.

First I built the two closer arches with a 15mm gap between the dome to allow me to stuff some fire rope between the arches, then I cut some slices of insulation brick and placed them between the two floors with a couple of mm top clearance to allow a strip of stainless steel to sit on top.

As I have a good half a bucket of expensive refractory glue I decided to use it. Maybe it's my imagination but it seems to be thickening as time goes by, so I had to squeeze the bricks really hard and carefully tap them down to get the required 2mm or less glue thickness. This made some previous joints move so I had to push even harder to try and get all the joins to close up. When the arch was finished I noticed it bulged out a bit, maybe 10mm on one side, the bricks no longer touched the template. Ah well, I don't think it's going to collapse, the next day it stood on it's own and the glue seems to really stick and hold tight.

I have a stash of pressed red bricks that I pulled up some time back that I'd been saving for this project. They were used as paving so there was no mortar to clean, just needed a good scrub to get the moss and dirt off. I wanted to keep using the refractory glue so each brick had to be cut to size. I really prefer this over mortar joints I reckon it looks nice and definitely won't crumble. I glued the back face to the fire bricks, (hope it holds) did a quick stack up to gauge the key stone then proceeded to glue and stack. Job done and I'm liking the look

I've also got some left over 400x400 glazed porcelain tiles, a charcoal grey colour that looks a bit like natural stone sitting next to the dome, reckon I might use them. Then I'll source a bit of granite to stick down on the entrance to save the floor brick edges from getting damaged.

Next I wrapped the fire blanket around the dome, got one layer around the bottom half and 2 layers on most of the top. Tomorrow I'll have to take a 400km round trip drive to get another box. That's the disadvantage of rural living.

[UtahBeehiver]

Nice job on vent stack.

[shanesmith80]

Very neat job on the vent.

Where did you get the refractory glue?

[Gretsch]

Very neat job on the vent.

Where did you get the refractory glue?

Thanks for the compliment, I got it from Claypave near Ipswitch, it's called Rylbond mortar, an air set product.
If you're around the Sydney area these places both sell something similar:

http://www.fieldfurnace.com.au/high-...uldables-c-14/
https://www.sydneyfirebricks.net.au/...es-insulation/

[Steady]

Job done and I'm liking the look

As you should be, its very neat and looks great

[Gretsch]

As you should be, its very neat and looks great

Hey thanks Steady and also UtahBeehiver

Im up to the vermicrete layer over the calsil blanket part. Ive got chicken wire in place and using the 10 to 1 mix and it’s not wanting to stick to the sides, it’s crumbling away. Tried 8 to 1 mix not much better.
Think I’ll try david c’s suggestion of a handful of powdered clay from my brick cuttings in the mix and see how it stands up.

[Gulf]

Forget trying to "stick it to the sides". Lay it from the bottom up, one course at a time. About 6" in height. By the time you get all the way around, the last course will be stiff enough to handle another.

[Gretsch]

Forget trying to "stick it to the sides". Lay it from the bottom up, one course at a time. About 6" in height. By the time you get all the way around, the last course will be stiff enough to handle another.

Yeah thats a thought that I had as well and started to do that but its not stacking well either and itll be a slow and long wait between courses...

BTW thats a nice looking dome you got there, is that concrete around the base ? Maybe to keep back the water seeping in ?

Another point is Ive used up a bag of cement to 1 1/2 bags of perlite! Thats a lot of cement!

So a change of tactics is needed and what I think Ill do is start laying down the brick shell and as it rises just pour in the dry perlite. Same idea as if it were a dog box. When I get to the curves Ill revert to the cement mix so I can lay the bricks back against the set perlicrete.

Now Ive seen UtahBeehiver (for one) has put a vent cap on the top of his dome to allow any moisture to escape. That looks like a good idea to me, might have to steal another idea from this fabulous forum

[david s]

Hey thanks Steady and also UtahBeehiver

Im up to the vermicrete layer over the calsil blanket part. Ive got chicken wire in place and using the 10 to 1 mix and it’s not wanting to stick to the sides, it’s crumbling away. Tried 8 to 1 mix not much better.
Think I’ll try david c’s suggestion of a handful of powdered clay from my brick cuttings in the mix and see how it stands up.

Take a handful of the mix and press it against the blanket for about 2 secs about 35 mm thick, making a flat top that you can form the next layer onto. I also find a mixture of vermiculite and perlite, half and half, makes a more workable mix than either of them alone. Adding more cement makes it more workable and increases its strength, but drastically reduces its insulating capacity. Once done you can tap the surface lightly with the flat of a trowel to get a perfectly spherical form by eye.

Make sure you wear gloves.

[Gretsch]

Well ended up doing what I said, building the outer shell up and filling it with dry perlite. I figured no cement in the mix would lead to better insulation and secondly I get impatient at times and my method eliminates a job and I'll be cooking pizza faster

This worked well on the vertical sides and as the curvature increased I was able to then revert to cement mix for the rest. I'm getting near the end, looks good from the photos posted here but don't look too close. The outer dome ended up not so round with a hump in one place and a crooked line of bricks on one side where the dome meets the barrel. Still, I'm confident it's not going to collapse, I'm the kind of bloke that will produce something that will last, but may not be pretty.

[Gretsch]

Make sure you wear gloves.

You bet!
Bought some latex (or something like that) specific for brick work, eventually wore through in one spot and the lime burnt a hole in my skin