2 meter diameter New build oven with pumice reinforced with Basalt Rebar

[MarkJerling]

I see you started off with night store heater bricks. I've built mine out of night store heater bricks. Coincidentally, I also have a foil layer under my plaster render layer. It's worked well. I do get some moisture ingress at floor level as my floor bricks project too far out the door of my oven, but the dome itself and the floor in the oven is good and dry.

[Alomran]

An aluminium foil bubble layer will be impervious to water. This will have the effect of trapping any moisture beneath it which may cause you further problems.So take it easy with the fires and don't rush to pizza temperature for some time. Do plenty of roasting and baking at lower temperature first.

You are correct. However I needed a protective layer for the ceramic blanket while it remains exposed to the elements since the galvanised mesh remained un-tiled for 8 months! Meanwhile, I left the bubble aluminum sheets layers overlapping loosely to breathe rather than water tight completely.

[MarkJerling]

Interesting project. I look forward to seeing it's completion.

[david s]

Following adding 100mm of ceramic blanket, an aluminum bubble insulation was added, then created a space for the 250mm pumice. This may appear to be an overkill, however the oven exposed to the elements due to local regulations that made it impossible to shelter the oven.

An aluminium foil bubble layer will be impervious to water. This will have the effect of trapping any moisture beneath it which may cause you further problems.So take it easy with the fires and don't rush to pizza temperature for some time. Do plenty of roasting and baking at lower temperature first.

[Alomran]

I am pretty certain it is the largest oven in the UK!

[Alomran]

After realising that no render or tiling can be fixed on any galvanised steel, a layer of Ardex R3E epoxy was added then a layer of sand was sprayed . Then after the epoxy was cured, I cleaned the sand to leave only the one stuck to the epoxy in order to establish a grip upon which I did the tiling. My Romanian friend Adrian carried the difficult task of tiling (partially).

[Alomran]

A galvanised steel mesh was used to create a shell that contain the loose pumice. Then realised that I couldn't render or tile immediately on galvanised steel mesh as it won't stick. So I added a layer of epoxy Ardev R3E, then placed immediately sand on top of the epoxy to create a rough surface upon which tiling was placed. Very Expensive!

[Alomran]

Following adding 100mm of ceramic blanket, an aluminum bubble insulation was added, then created a space for the 250mm pumice. This may appear to be an overkill, however the oven exposed to the elements due to local regulations that made it impossible to shelter the oven.

[david s]

230mm thick dome walls is huge. Normally bricks are cut in half (4”) resulting in walls half that thickness. If you only have one inch of blanket and want to back it up with vermicrete then it’s important to keep it as lean as you can because the cement reduces insulating capacity. Not sure about the wood ash addition. I use a bit of powdered clay to assist workability. Wood ash is light but quite caustic when mixed with water and handled. We use it as an ingredient for glazes. It’s composition varies greatly depending on what wood is used.
Creating an insulation layer with wet material is a problem because you need to dry the stuff out. Apply it in layers around an inch and a half thick with at least a week drying between layers. Firing an uninsulated oven is a recipe for producing cracks and this probably contributed to your problem.

[Alomran]

Given that the internal dome is 98cm in radius with a full brick in thickness (230mm) making the external shell of the sphere about 9.5 meters which is very expensive to insulate with ceramic blanket, would it be sufficient to have 1 inch of ceramic blanket and compensate that with 6 inches of pumice with vermiculite?
I have enough pumice to make it about 6' or even 8" inches thick. ALso, would fine wood ash be ok to be added to cement to make it workable ? I know ash is used in old cultures of the far east when mixed with clay as a waterproof.https://www.youtube.com/watch?v=mn1DEeyqaT4

[david s]

If you already have blanket one layer should be sufficient. To get the correct consistency for every 10 parts of vermiculite(or perlite) add 3 litres of water. If you have some powdered clay a handful of it for every litre or so of cement will give it mor workability.

[danhem]

So, the usual method is to give the blanket a layer or two of lean (10:1) vermicrete which evens out the lumps and bumps and once set and dry is firm enough to render against while also providing an extra insulating layer. If it is made any thicker than an inch or so, then drying becomes difficult. When I first began making ovens the older generation of blanket was not classified as safe and the safe stuff now used was prohibitively expensive. Consequently I insulated entirely with 10:1 vermicrete and quickly found that it was best done in layers of around one and a half inches thick with a week of drying before proceeding to the next layer. I now use a blanket layer over which I do a vermicrete layer, then after a week of drying the drying fires and finally the rendered outer shell. [ATTACH]n418076[/ATTACH]

Hi David,

Im about to set too with the v-crete layer. Am I mixing 10:1 vermiculite/portland for this purpose? And as far as hydration, what kind of consistency am I looking for in the mix?

From your post quoted above, am I right in thinking that 2 layers of 1.5" each are applied or is 1 layer of 1.5" sufficient (I have 3" of blanket insulation over the dome)?

Thanks,

Danny.

[david s]

Ok. You can’t undo it short of a total rebuild and repairing internal dome cracks is rarely successful so just use the oven as planned. It should not alter its performance and it won’t collapse. You’ve just joined the crack club.

[Alomran]

I did warn you that if you see visible steam then you’re going at it too hard. What’s done is done. Your oven won’t fall over because the dome is a self supporting structure. Just continue with the drying fires gently until all the black soot has burned off right down to the base of the dome.

David the steam I saw was coming from parts of the wooden frame shaping the dome and not from the bricks, My mistake was I lit a small fire amd left it for 2 hours unattended that must have started on a small part of the wooden frame and spreaded.

[david s]

I did warn you that if you see visible steam then you’re going at it too hard. What’s done is done. Your oven won’t fall over because the dome is a self supporting structure. Just continue with the drying fires gently until all the black soot has burned off right down to the base of the dome.