Pre-build planning, Darwin- Australia

[Wheatdog]

G'day to all,
I'm in the process of gathering materials and planning the build for a 1000mm internal diameter pompeii oven.
I have managed to find 210 SK34 firebricks (230x115x65mm) and approx 50 insulating firebricks (isolite B8)
From what I have read on the forum my plans are as follows, any improvements / feedback is welcome

Base-
re-enforced concrete on dry stacked blocks (core filled with reo)
Mosaic tiles with drain holes in the slab, should water ever make its way in (will be in an undercover area)
Insulating firebricks 230x115x65mm
CalSil board - I'm debating weather to go for 1 inch or the 2inch thick as there is significant insulation provided by the insulating firebricks..
SK34 fire brick base, herring bone pattern with slight chamfer on all upper brick edges

Dome
Dome to be built on top of the base to ease any thermal expansion issues
Bricks will be cut using the "Mr Chipsters" Jig in conjunction with the pompeii dome calculator spreadsheet using I.T. method construction
Mortar- Unsure to make my own "homemade" or buy the high temp premade bags
Insulation Ceramic fibre blanket, 2 rolls making approx 100mm layer over the dome
Chicken wire and roof tile pointing to render (stucco coat) and potentially tile as final layer

Inner arch and Flue arch
SK34 fire bricks for the inner arch using the same dimensions as Mark Jerling provided in his plans
Outer arch, Depending on qty of bricks remaining might use fire bricks or just general kiln fired bricks
Looking for guidance on weather a thermal break is going to be worth the effort.
The outer arch is the part I'm not completely sure on how to construct and tie into the inner arch.
From what I have seen having a taper leading up to the flue on the surrounding bricks would help with draw and prevent smoke coming out the entrance

Look forward to any advice or tricks to help with the build..
Cheers...

[david s]

Hi Wheatdog,

You’ve obviously delved into the forum for info as your plan sounds well researched. Here’s my two bobs worth.

The cal sil board is expensive stuff and the 65 mm of IFB already provides excellent underfloor insulation. There comes a point where the addition of insulation vs cost is subject to the law of diminishing returns. If it were mine I’d be choosing the 25mm cal sil.

On using either homebrew or refractory mortar, apart from the much higher cost, the refractory mortar is much more difficult to use. Because it contains calcium aluminate cement, it goes off really fast, resulting in very short working times. This problem can result in very weak mortar joints if the stuff is rewetted and used after it has started to harden. Unfortunately it is also highly temperature dependent, that can be offset by using chilled water, something you would need to do in your climate. It is further disadvantaged because recommendations are that it only be used for thin mortar joints. As there is a considerable volume to be filled on the outside of each brick on the dome a very thick joint is required there. The homebrew by contrast is cheap, with extended working time and has proved adequate for most home builders. Perhaps you could reserve the refractory mortar for the top third of the dome which will see higher temperatures (backfilling those joints on the outside with homebrew).

On using the IFB for the flue gallery, although they will perform well to prevent conductive heat loss from the dome, they are very brittle and vulnerable to damage particularly around the door rebate and low down near the floor.

The flexible pointing is not suitable as a render. It has been designed to cover mortar in a thin layer, providing a flexible weatherproof impervious layer. If used over a standard cement render it performs extremely well and has the ability to bridge small cracks. For ease of application I dilute it 20% with water so it can be applied with a brush. 3 coats results in a thickness of around 2mm.

Dave

[Wheatdog]

Thanks for the Info Dave, it is much appreciated mate.
Yes I have been down "the rabbit hole" of information on the forum and the passion from some of the members is truley inspiring.
I will use home brew as suggested, and just go with 25mm CalSil.
What is the best recipe for the "homebrew"?
The refractory cement i was looking at is Calucem Istra 40, available from Bianco hardware which as you mentioned might be worth using at the top of the dome
Compared with normal cement it is expensive but 1 bag should be more than enough for the build $52.80 (not pre-mixed)
I am lucky and have forum user "Terratree" up the road who has offered to lend me his brick saw and has a left over bucket of refractory brick dust.

With regard to the thermal break if anyone out there has plans/pictures of how they constructed their arches with a thermal break incorperated it would be good to see

Good info on the render, I have never actually had to render anything so I am only just learning.

I have created some form work for the arches and now need to make an IT tool.

Unfortunately the build will be a while off getting started, as I want it to be in an undercover area which is also still in the planning stage.
Thanks for the information. I will post some pictures as progress begins.

Thanks again to all that have posted with tips and tricks..

[david s]

The home-brew recipe is 3:1:1:1 by volume Sand (use bricks sand or silica sand), Clay (use bricklayers clay, try Lyndons), Lime (use hydrated lime, try Bunnings), Cement (use GP cement also try Bunnings, but as they only stock the Vietnamese stuff which only just meets Australian standards I prefer to use Cement Australia cement even though it's a little dearer)

Make sure, if you use the refractory mortar, to use chilled water or it will go off faster than you can use it.

With the outer render I use AR glass fibres for reinforcing, but you can use the small mesh chicken wire (cheaper but way more time consuming to apply and render over because of the compound curve problem.

[Wheatdog]

Finally got around to digging the footings and building the stand for the oven.

400mm footings, N16 Starter bars, dry stacked blocks - core filled, N16 reo mesh and custom made cast plates for a small roof.
Poured the supported slab with 40mPa concrete with AR Fibre mixed in. 3/8 stainless steel drain holes x5

I'm letting it set for a few days before removing all the form work, Just in Case...

Thanks to David S and Mark Jerling for their advice and Terratree for lending me his mixer and wet saw, also helping with the footings

[Wheatdog]

Before proceeding with the base, I am wondering if I should cover the CalSil board with heavy duty aluminium foil.
The base / under floor will consist of tiles to assist with drainage, 75mm thick IFB's and 25mm CalSil board.
The foil would protect the Calsil from moisture coming in from above, but could also trap the moisture below. I have 5 drain tubes in the slab, but will it still trap the moisture?. Being in Darwin- Australia, it is humid most of the year and rainfall is also very heavy in the wet season.
Please offer your opinions the foil layer..
Note: There will be a small roof overhead but I still expect some rain to hit the external surfaces

[JRPizza]

I see you welded your rebar. I had thought about tacking mine to get some practice, but my neighbor had experience and tools so he wire tied it for me. Was curious about your "custom made cast plates" - did you cast them yourself?

[Wheatdog]

Hi JR, the cast plates refers to the metal plates anchored within the concrete casting. I just needed the bars to be spread through the slab as there will be a small roof above the oven and the vertical posts will be welded to them.
As for the welding of the reo mesh, I had the welder out from fabricating the plates and just decided it was a lot easier to tack everything in place. Not sure about the science behind tying vs welding, however as pretty much every concreter ties them, I'm sure that would be the preferred method.

[JRPizza]

Once the cement cures I don't think it matters how the rebar was held together. I asked about those details as I am always amazed at the things oven builders do during the process, and thought you might have been casting your own parts. That would have been most impressive
I hope you document how your roof goes up and show some good pictures of the weldments attaching the roof. I can't recall any other builds that had a welded on roof structure.