30" cast pizza oven - scotland

[david s]

Just cut a thin stick to the required length and place it in the centre. Then build the sand around it. To reduce the sand quantity you can put some empty plastic bottles near the centre at the base and build the sand over them.

[Daveholdn]

Hattori-Hanzo Thanks very much, I'm more than certain I'll do a sand mould now. I can get the circumference of the sand mould by marking it out on the firebricks, but how do you get the height of the sand mould? Just a case of measure and guesstimate from there?
Thanks for the info

[Hattori-Hanzo]

Reading this with interest.

For the insulation layer over the ceramic blanket an 8 or 10 parts vermiculite to 1 part cement.
As I understand an 8-1 mix should be slightly easier to work with but reduced insulation.

10-1 is a bit harder to work but slightly better insulator.
The more cement you add to the vermiculite mix the worse the insulation properties get.

I would also look into casting over sand. The problem with an oven your size is a gym ball can deflect and sag under the weight of the cast.
Another problem is you have to build a lot of form work under the gym ball and some how remove it all once the cast is done increasing the risk and chance of cracking the dome.

Casting sand is fairly straight forward, to get a good shape cut the desired half round from a scrap of wood and use that as a former to smooth the sand to a nearly perfect dome.

Good luck with the build, keep us updated.

[Daveholdn]

Hi utah, thanks very much for the welcome and the information. Apologies, I meant a 2" vermiculite mix over the ceramic blanket. When you say 8-10 vercrete, is that an 8-10 part vermiculite, 1 part portland cement mix to shape around the the blanket?

I'll have a look at the other ovens being conctructed and already was half thinking about an in situ mould over sand. I take it with the sand mould, builders sand will do and just a case of shaping the sand to as best a dome shape to the dimensions you can? There's no special way of doing it?

I've read a lot of the stuff from David S, and a multi part cast seems to make for a more effective dome, rather than an all in one cast, but again is there any special way of doing this over sand?

Thanks again and sorry for all the questions, cheers.
Dave

[UtahBeehiver]

Welcome to the forum. I am glad you visited before you got too far along. These YouTube videos can be really bad and one offs (there are some good ones though). There are a number of cast ovens going on right now especially in the UK area. So look in the Other Type of Oven section and also lean heavily on David S of Australia threads, he is out resident cast expert.

5 to 1 vcrete is correct for under the fire brick.. Is there a reason for the 2" refractory over the ceramic blanket (shape?) consider 8-10 vcrete for shaping and added insulation as base for render. A in situ sand mold is recommended over a gym ball, See current builds

[Daveholdn]

Hi Team,

I took the plunge a few weeks ago after watching a you tube video series on building a cheap pizza oven, and basically thought i was an expert!! How wrong i was after stumbling across this forum and got the vibe, if your going to do it, why not go the extra mile and do it properly!

Attached are the pics of where i am at;

I laid a 4" thick, 39" x 47" concrete foundation and built a small block base, initially with 2 legs, but added the 3rd, middle leg in for support after reading forums on here.
I've then placed 4 x 23.5"x 23.5" (2" thick) paving slabs on top as part of my sub-base.

Thats where i am at, i plan, unless the expertise on this forum say otherwise, to:

Build a 47" x 47" form and pour a, 47" x 47", 5:1 vermiculite/portland cement mix slab, at a thickness of 2" on top of the slabs to complete the sub-base.

Then lay 2 x 1" thick ceramic fibre boards as insulation directly on top of the vermiculite concrete.

Then place my fire bricks on top in herringbone formation.

Use a gym ball to cast a 2" thick, refractory cement mould, appox 29-30" internal diameter, and then place this on top of the bricks, ensuring no bricks are touching the vermiculite sub-base.

Insulation around the dome will be, as mentioned, 2" refractory cement, 2" fire blanket, 2" refractory cement and then 1.5" render to finish.

The flue gallery, i'll have to get my head around, more reading required.

If that sounds like it would blow up in my face then please let me know, i'm extracting info from this site all the time and trying to put it into my own build.

My first question is; as per the pics, I've placed 4 x 23.5"x 23.5" (2" thick) paving slabs on top as part of my sub-base, these where bought in haste after watching the youtube stuff but i'm now worried these wont cut the mustard with the potential amount of weight of the oven going through them? Is there anything i can put into the vermiculite slab to reinforce or does this defeat the purpose of the insulation slab?

Also, what is the best way to mix the vermiculite/portland mix for the slab? i'm going to use a shovel and a mixing board as i've read using a mixer can break the vermiculite down too much. I've also read you need to add a bit more water to the mix as the vermiculite is thirsty, but what kind of consistency should i be looking?

Any info or direction would be much appreciated, and thanks, great forum.

Dave.