2025 Pompeii Oven Build Log

[yoboseyo]

Update:

Completed the brickwork for the outer arch.

Also fixed up the inconsistent thickness of perlite.

I left a 20mm gap between the inner and outer arches for the door. There's going to be a landing slab placed on the bottom row of brick.

There's also a 25mm thermal break between the inner and outer arches, which I will fill with heat-resistant rope.



Put a wedge of brick to straighten the path of exhaust and support the vent

[yoboseyo]

Vent Design Questions:

Hey guys, time to design the vent and I am in need of assistance.

The vent construction is going to sit on top of the inner and outer arches. My idea is to stuff leftover pieces of CaSi in the thermal break (cut into L shapes so it fits not only the thermal break but sit between the vent construction and inner arch) to define the flue opening.

The arches were designed this way because the outer arch is normal brick (kilned) not firebrick. Insulating the vent as much as possible from the inner arch minimises heat leakage to the outer arch.

Illustration:


I've done extensive reading of this forum on vent design and this is my design so far:

Vent dimensions:

• Chimney size: 150mm/6"
• Size at opening: 400mm*200mm (more than double the chimney size)
• Reduction to chimney at a 60deg angle (I read that it should be 30deg - not sure whether that's 30 from horizontal or vertical - I assumed taller the better)

Sample Sketchup:


Questions:

1. Any advice/critique on the proposed vent design?

2. What should I construct the vent from? Options are:

• Brick - I may have trouble getting the ideal sloping shape using brick
• Castable
• Steel

3. Can I use this recipe for castable? These are the ingredients I have (castable refractory is not available here) Coarse sand:crushed firebrick:ciment fondu:fireclay 3:1:1:1

4. Should I insulate outside the vent?

5. If not insulated, can I apply the same rendering on the dome, which is mosaic tiles adhered using thinset to the flue? Or will it be too hot? Is there such thing as refractory tile adhesive?

[david s]

I think your solution is pretty sound, but it may lead to exposed cal sil at the sides of the entry and the stuff is not particularly strong so would be susceptible to knocks and abrasions there. Casting the vent transition is way easier than building that kind of form in brick. It also allows for a big reduction in weight and therefore heat sink.
i’ve found the 3:1:1:1 recipe leads to excessive shrinkage (you don’t want shrinkage cracks), from the high clay portion so I halve it, with much better results. 3:1:1:0.5, but you will need to add the very fine polypropylene burn out fibres for steam spalling protection. A casting thickness of one inch should be sufficient.

[yoboseyo]

exposed cal sil at the sides of the entry

I will seal all the edges of the transition using rope

I’ve found the 3:1:1:1 recipe leads to excessive shrinkage (you don’t want shrinkage cracks), from the high clay portion so I halve it, with much better results. 3:1:1:0.5

would it be better to omit the fireclay entirely?

fine polypropylene burn out fibres

I just looked up this stuff. It comes in different fibre lengths from 6mm to 18mm. which should I choose? how much of it do I need to add?

Do you have any experience with tiling on hot surfaces? Would I be able to lay tile directly on the vent? I read in another post of yours that you have used Monoflex, which I can get. That wasn't for a vent, though. I'm not sure how hot my vent will get.

[david s]

Don’t omit the clay in the recipe entirely, it adds refractory quality to the mix as well as making it more workable. The very fine polypropylene fibres I use are 19 mm long and added at the rate of 1% by volume. Be careful to disperse them well in the mix, they tend to clump. Mix for double the time you would normally expect.