Is this design OK?

[angelboy]

I'm planning to build a 90mm (3.5") reinforced concrete hearth which will overhand the oven stand by 25mm (1") on three side and a 125mm (5") curved front. On this I was planning on 100mm (4") vermiculite and cement insulation layer (I'd heard that the ceramic boards can get damaged in the wet and as I'm in the UK it's wet a lot!) with a 50mm (2") firebrick oven floor - both layers being exactly the same size. I was going to put a course of bricks standing up on the outside of the vermiculite layer, which will be the first course for the oven dome.

Is this right, or do I need to extend the vermiculite layer so that the first dome bricks sit on it, effectivly being bigger than the oven floor layer?

[UtahBeehiver]

I suggest you read and download the free eplans from Forno Bravo. It is a good, but dated baseline on design and construction. There is one critical problem with the current design, the bricks need to be on the insulation and not on the hearth. You can also look in the Newbie section under Treasure Archives sticky, this show some of the more documented builds. You can also look and Nick JC's build, he did a really nice cast build and is from the UK.

[fox]

Hi angleboy, If you are planning on using vermiculite board it wont last as well as ceramic fibre board as vermiculite board contains a fair amount of clay that will dissolve when wet.
I use ceramic fibre board on all my builds (14 so far) and I live in Guernsey so similar weather to you.
Better to build with a good design that wont allow any water ingress.

[angelboy]

I suggest you read and download the free eplans from Forno Bravo. It is a good, but dated baseline on design and construction. There is one critical problem with the current design, the bricks need to be on the insulation and not on the hearth. You can also look in the Newbie section under Treasure Archives sticky, this show some of the more documented builds. You can also look and Nick JC's build, he did a really nice cast build and is from the UK.

Thanks for that - I’ve downloaded the pdf but I’d missed that newbie thread completely.

[angelboy]

Hi angleboy, If you are planning on using vermiculite board it wont last as well as ceramic fibre board as vermiculite board contains a fair amount of clay that will dissolve when wet.
I use ceramic fibre board on all my builds (14 so far) and I live in Guernsey so similar weather to you.
Better to build with a good design that wont allow any water ingress.

The problem I think I might have is it getting wet during construction. You know what the weather is like over her. Yesterday morning it snowed and by the afternoon it was like a spring day. The snow wasn’t on the forecast when I checked at the start of the week either.

I was planning to use vermiculite mixed with cement and water so that it becomes hard. This wouldn’t be the same as vermiculite boards.

[fox]

No it would not be the same but it wont have anywhere near the same insulating properties either, but there are no pizza oven police so you must do what you feel is best for your own project.

[Pizzarotic]

Is this right, or do I need to extend the vermiculite layer so that the first dome bricks sit on it, effectivly being bigger than the oven floor layer?

Your floor insulation should extend out to the outside of the dome so your first course of bricks are insulated otherwise they will be a source of heat loss. Also the vermiculite floor installation is usually extended 2" or more past the dome so the dome weight is not on the edge of the vermiculite which would be structurally unsound.

4" of 5:1 vermiculite is approximately equivalent to 2" of ceramic board so you insulation will be adequate.

[UtahBeehiver]

The amount of insulation depends on the type of cooking you are planning on doing. 2" of ceramic board is the min. amount but if you want extended cooking the more insulation may be required.