Mobile Pizza Oven (Pray for me)

[bearsparko]

Apr 22, 2017 22:58:32 GMT simon said:

Apr 20, 2017 12:21:42 GMT bearsparko said:

Hi Simon,

I have had a look at a few options with the exercise ball construction, and I quite like this one;
www.youtube.com/watch?v=fsOBp5pDBro&feature=share

It looks much more robust than the normal type, but I think I would use vermiculite as I have a local supplier, using a 80 or 85cm exercise ball.

What do you think? Any obvious concerns?

I'm kicking off this weekend as the procrastination is getting too
Much.

Thanks.

Hi, sorry for not getting back quicker, I've been offline...

That video does show a little more height than some of these exercise ball shaped ovens, which is better IMHO.

As someone else has said, it would be better (and cheaper) to just have the fire bricks for the hearth, and not extend out. Losing heat is not really an issue in your case I'd say, but you could have a very high temperature outside of the oven dome, which could burn someone/something. It would also make finishing the dome, to make it weather proof much harder.

Now what to actually cast with? Vermiculite should be fine, but Portland cement less so. As mentioned it breaks down with high heat, which is why you see various home brew mixes for mortars etc. The trouble with adding something like clay is you lose insulation, you have to source another material, and it will shrink and crack and be horrible to work with.

As already mentioned there is another type of cement that is regarded as a refractory cement, Calcium Aluminate. It will survive the heat, but it sets quickly. You will have a much shorter window of working time. It is unlikely to be stocked at a local merchants. However you will easily be able to get fast setting cements. These are a mix of Portland cement (calcium sulphates) with fast setting calcium aluminate. If you want a vermiculite dome, I'd make it with that. Make small(er) batches, mould, repeat.

Good luck.

Hi Simon,

I have been investigating some alternative cements and I can source Cement Fondu, which I think is what you are talking about. Also I have realised that I can get perlite from the many hydroponics retailers around so I am thinking about switching to perlite for the dome as I think the whole thing will cure quicker. I have also seen a post where they added short glass fibres to the mix to strengthen the dome which seems like a good idea for little additional cost.

I was going to put a layer of fibreglass insulation around the outside and then use an weatherproof render to protect the oven, in the normal way of finishing a dome, but you said that "losing heat" was not an issue in my case? Is there really no benefit to insulating?

Thanks again.

[downunderdave]

There is a great deal of work in making the formwork in that video. Even when the casting is complete it has to be lifted into position. It is far easier to build a dome sand castle over a fire brick floor, using 8% water and a little powdered clay in the mix. Cover the sand mould with thin strips of newspaper and cast the dome over it, then tunnel the sand out once the casting has set. If you get the mix consistency right there is no need to have an outside mould. If you want to go down the route of calcium aluminate cement (ciment fondu) and create your own castable then you should consider using a proprietary dense castable refractory. Calcium aluminate castings have the added benefit of achieving their full strength in 24 Hrs so no prolonged damp curing required like portland cement castings require. The usual method is to have a strong dense inner layer which is more conductive and will store more heat with its high thermal mass, and then insulate it well. I suggest you skip the fibreglass insulation (I presume you are thinking ceiling insulation). I used it for my first oven and found it difficult to shape and fit the pieces because it compresses so easily, would never use it again, some have said the binders used can't take the heat although mine was still in good condition when I replaced the oven. Ceramic fibre blanket by contrast is more dense, doesn't compress as much and is beautiful to cut and fit.It is however, more expensive.Make sure you get the new generation ceramic fibre that is exonerated as a carcinogen, Using a 10:1 vermicrete is cheaper almost as good an insulator, but takes more work to apply and must be dried before building over it.