Insulation layers on 3G MTo Oven

[wilef]

I'm trying to follow Rado's style of pizza oven and have built the foundation and concrete block base so far. After that he shows layers of concrete capstones, vermiculite/perlite (4in pour with cement 5:1), then a concrete pour (high temp concrete, very expensive), followed by the fire brick floor.

I've got the concrete capstones and am considering the vermiculite step but am intrigued by the ceramic board option as this seems a lot easier. I'm wondering, for anyone who has done this, can I eliminate both the high temp concrete and the vermiculite with the ceramic board? Any advice would be appreciated!

[david s]

It depends on how much thermal mass you want to have in your oven. The thicker the walls and floor the longer the heat up but also the more heat that can be stored for extended retained heat cooking. Normally the floor brick thickness is about the same or a little less than the dome thickness. This means a floor thickness of between 2-4” normally, so it depends on how thick your floor bricks are. I suspect Rado’’s addition of more refractory concrete under the floor bricks is to compensate for thin floor tiles. If using firebricks for the floor the thickness will usually be around 3”. If laid on their sides it can increase the floor thickness to 4”.

There are a number of different materials that are suitable for underfloor insulation, but the 5:1 vermicrete is probably the cheapest.

[wilef]

Thanks for the info David, makes sense. So let's say I use firebricks 'flat' at 2.5", under that use ceramic fiber board, under that 4" vermiculite, and below that the concrete capstone 2". Given that I'm not too concerned with cooking the next day with heat retained overnight, does this sound suitable?

[wilef]

Correction, the firebricks would be placed on end, so you'd get a floor of 4.5" of fire brick in addition to the ceramic fiber board, 4" vermiculite and finally concrete capstone. If anyone else has done a similar stackup, I'd love to hear how the heat retention has worked out.

[Karangi Dude]

Hi Wilef, Given that you are not too concerned with cooking the next day with heat retained overnight,

If this is the case I think you are looking at building the wrong oven Rado and Scott ovens are predominantly bread ovens that take a long time to heat up (and a lot of fire wood) but retain that heat for extended periods for baking etc. the 3G MTo oven has about 9" of thermal mass hearth and walls, most commercial pizzeria's only have about 2" of hearth thermal mass they heat up quicker, they retain heat for cooking pizza with an active fire on the side.

I have built a barrel oven that you may be interested in it has lots of insulation and nowhere near the amount of thermal mass as the 3G MTo oven
https://community.fornobravo.com/for...rel-bread-oven

Cheers Doug

[P3 Stoaker]

G'day Wilef,
I'm just in the process of building the base and designing the structural layer (hearth) and insulation layers. The oven is for domestic use and along with you I'm not trying to cook in it for days from the same fire up.
I learned 2 interesting points in the last 24 hours on this site, earlier post.
1 Don't let the dome or oven floor bricks touch the hearth or it will act as a heat sink, and
2 Caution with fibre board or silicate board in respect to compressibility, especially if fibre board gets wet.

If anyone has thoughts/recommendations/experience good/bad in relation to the following please let me know.
I have about 6 and 3/4 inch thickness to work with for structural and insulation layers. It's been difficult to determine if the fibre or silicate boards are suitable to have the dome and floor bricks laid directly on them. I cant really sink the board in and cover with high temp mortar as that would reduce the structural layer too much. Bottom line is I intend to use a little under 4 inch of structural concrete and a little over 3 inch of perlite on top of that and lay the dome and floor directly on the perlite. I have 2 relatives that very very successfully cook loads of pizza's in their ovens and they don't even have an insulation layer. Sure 3 inch of board would be nice but I can't see it preventing you from achieving a great result. I welcome your thoughts
Kind regards