New 42" Pompeii in Alberta

[jbergen]

I feel like I've read about a million posts in the FB forum -- thanks everyone for being so generous with your experiences. I've got a Pompeii kit sitting in my backyard, and the time is coming to put all that reading to work.
I have a professional welder friend who is going to build me a stand for the oven, so I can skip the concrete block process. Footings will be 10" pipe buried about 3' in the ground, to which the legs of the support stand will be attached.
Questions!
1) is there anyone who's gone this way (metal stand rather than cement blocks) who has an opinion on whether a concrete pad poured onto the top of the stand is necessary to support the oven, or whether I could build directly on the stand itself (starting with the insulating layer)
2) the floor tiles FB is now supplying are 2" thick. The primary purpose of the oven will be to bake bread. Should I consider adding 1 1/4" firebrick splits under the floor to increase the mass somewhat?
3) do I need to use firebrick for the floor of the vent landing? And what about an insulating space between the front of the oven floor and the beginning of the vent landing so that I'm not losing heat to where it's not needed (i.e. the vent landing floor?
Looking forward to learning from those with much more experience than I have!

[wotavidone]

Re: New 42" Pompeii in Alberta

I've always got an opinion.
1) Unless the top of your stand is seriously thick and solid steel say, 3/8 + inch maybe, pour a reinforced concrete pad over thin sheet - 4 inches thick with mesh in it would do.
The idea is to have something that doesn't flex, buckle, warp or sag. I don't know Canadian prices but, here in Oz, a concrete slab over a bit of roofing iron was cheaper than a piiece of sheet steel I thought would be strong enough for the weight.
2) 2 inch firebrick is fine for a pizza party and a batch or two of bread after. Adding a layer of splits would make it a serious bread oven.
3)Lots of people add a heat break to separate inner arch from outer arch. It is probably best practice to do so... If you do, everything inside that heat break should be fire brick, and you can probably get away with ordinary fired clay bricks outside the heat break.

[jbergen]

Re: New 42" Pompeii in Alberta

That's a great help; thanks. So by a "heat break" you mean a narrow space between the floor bricks inside the oven and those on the vent floor? Under the floor, I'm using the 2" ceramic insulation that FB supplies. So I would start with that (on top of my cement pad), then the firebrick splits, then my floor tiles...sounds like quite a pile of pieces even before I start building the dome. I'm thinking I should mortar the underfloor splits and/or pour insulating concrete around the floor base for stability. Thoughts?
Jamie

[wotavidone]

Re: New 42" Pompeii in Alberta

That's a great help; thanks. So by a "heat break" you mean a narrow space between the floor bricks inside the oven and those on the vent floor? Under the floor, I'm using the 2" ceramic insulation that FB supplies. So I would start with that (on top of my cement pad), then the firebrick splits, then my floor tiles...sounds like quite a pile of pieces even before I start building the dome. I'm thinking I should mortar the underfloor splits and/or pour insulating concrete around the floor base for stability. Thoughts?
Jamie

2 inches of ceramic insulation is good. Put that on top of your cement slab or thick steel platform. Then floor on top of that.
After that I am at a bit of a loss - I've often wondered how you get a decent physical connection (which I think you would need to get the full benefit of the extra mass) if you have more than one layer of floor brick.
It's not usual to mortar floor bricks, I think the expansion/contraction would soon put paid to mortar.
Most people seem to bed the bricks in a layer of sand/clay mix, maybe a thin layer of that would marry the floor tiles to the fire brick.
Others must have done it, perhaps they'll chime in and tell us how.

It is a pile of bits before you get to the dome - that's one of the reasons I personally chose to put the floor inside the dome - I wondered whether I could supply a stable layer to put the dome on.
Most consider it simpler to put down a floor then build the dome on top.
There would be a bit less cutting that way.

By heat break, I mean a gap of maybe half an inch between cooking floor bricks and vent landing bricks, and carry the gap up between inner arch and outer landing/vent arch. Basically, you disconnect anything that would be outside the door if you closed the oven up to conserve heat for tomorrow. Most bridge the gap in some way - some insulating fibreglass rope, some perlite cement, or some such. Anything to stop heat from the oven dome or floor from "wicking" out to the bricks outside that are exposed to atmosphere.
Search "heat break" and you should find heaps of examples.

[oblertone]

Re: New 42" Pompeii in Alberta

Not exactly the same but my build (see below) was built in a steel tray, I used 25mm of vermiculite board and then 50mm (2") thick firebricks for my floor. During use the underside of the pan can reach 80c but I can happily cook bread/roast the day after a pizza burn. With hindsight a 50mm layer of insulation would improve things but it's not a game changer as my oven does what I need it to do. The mantra about not being able to retro fit under oven insulation is very true; good luck.

ps - The steel in my tray is only 3mm but it is heavily braced as you can see in the early pics.

[jbergen]

Re: New 42" Pompeii in Alberta

Thanks, oblertone. Hope the Italian nights are going well and that the ends of your fingers healed up ...

[mrchipster]

Re: New 42" Pompeii in Alberta

2 inches of ceramic insulation is good. Put that on top of your cement slab or thick steel platform. Then floor on top of that.
After that I am at a bit of a loss - I've often wondered how you get a decent physical connection (which I think you would need to get the full benefit of the extra mass) if you have more than one layer of floor brick.
It's not usual to mortar floor bricks, I think the expansion/contractilon would

Hi, Alberta is in a very cold part of North America.

I live in Minneapolis Mn. and we have similar weather. I have over 4 inches of insulation below my floor and that is my greatest heat loss location on my oven except for the door.

When it is 10F and the oven is saturated to 500F the under slab (4inch) temp is 60F and anywhere I measure (ex. Door) the outside is the same as the current air temp.

It takes a great deal of energy to heat a 4 inch concrete slab 50 degrees when there is significant air movement arround a major surface.

I would use 6 inches of ceramic or combo of ceramic and Perlcrete layers

I would also take the rest of the prior entry to be spot on.

[jbergen]

Re: New 42" Pompeii in Alberta

Thanks, Chip. I appreciate the advice. I'll revise my underfloor insulation plans. What's your opinion on adding firebrick splits under the 2" FB floor tiles, for increased mass? Thoughts seem to be divided on whether this is desirable for larger-quantity bread baking.
Jamie

[mrchipster]

Re: New 42" Pompeii in Alberta

It makes logical sense to me that a thicker floor would help with heat retention, but I have not baked more than 2 loads of bread at a time . That was 20 - 1 kg boules 10 at a time. Depending on the size, shape and insulation you can do quite a bit of bread in one heat cycle.

You could always space out your proofing by 2-3 hours or so and reheat a little. It does not take much wood once the oven is at temp. And saturated to bring it up quite a bit in very little time. But as is often said each oven behaves differently.