800 mm homebrew cast

[sergetania]

"With the dome height of only 400 mm you really don't want the flame any closer to the top of the pizza." I'm not sure how you come to that conclusion.

I have to restate that. I will stick with my observations this time. In my oven with the dome height of ~325mm the flame rolling under the dome is close enough to the top of the pizza to cook it very quickly. With the oven floor at 800-900F the pizza is cooked from both top and bottom within 90-120 seconds. Basically, I wanted to say that the mentioned requirement that an oven should have a lower dome for neapolitan pizza probably makes more sense for larger domes. With smaller domes, the flame is already close enough to cook neapolitan pizzas very quickly.

There, I believe I have made a much more reasonable statement this time!

[Linuc]

With any oven you need a flame on the side to cook the top faster, but also to maintain the high oven temperature required for 2 min pizzas, whilst cooking with the door off.

"With the dome height of only 400 mm you really don't want the flame any closer to the top of the pizza." I'm not sure how you come to that conclusion. My experience with my hemispherical ovens which have a dome height of only 270mm is that the fire on the side with flame travelling to the top of the dome, works perfectly. Remember that a smaller dome requires a smaller fire. Some folk believe that a smaller oven chamber will heat up quicker than a large one, however in practice they're much the same because a smaller chamber requires a smaller fire. In the case of heat up it is the thickness of the floor and oven walls that is a more determining factor for heat up times.

So david s , what dome height would you suggest for an 800 mm ID oven specialized for neapolitan pizza? Is it possible to cast an oven that will cook the pizza in 60-90 seconds? I guess I need to get up in temperatures between 500-550 celsius (930-1020 F).

[sergetania]

Linuc

I am not David but it's definitely possible because that's what my oven does (built with David's help). When my floor temp reaches 800-900F it cooks pizza super fast. Definitely complies with the AVPN guidelines. If you heat the oven more pizzas start burning, the bottom chars and tastes bitter

[Linuc]

Linuc

I am not David but it's definitely possible because that's what my oven does (built with David's help). When my floor temp reaches 800-900F it cooks pizza super fast. Definitely complies with the AVPN guidelines. If you heat the oven more pizzas start burning, the bottom chars and tastes bitter

The your floor - fire bricks I guess - have too high thermal conductivity. Thats not the case with the biscotto floor I've bought. It's morse porous than fire bricks and you can heat up the oven more without burning the bottom. With biscotto you should be able to heat the oven to 1000 F without burning the bottom.

Well, at least according to the research I've done. Myself I dont have a clue

[david s]

From oven owners reports, all oven floors are too hot for the first pizza. It's rather like cooking the first pancake which is never the best, but subsequent ones are fine. The remedy is to place the first pizza partly in the entry which is a bit cooler, and rotating it about every 20 secs. The second and subsequent pizzas can be placed a little further in as the sting is taken out of the floor.
The semolina test for floor temp is a good one. Cast about 1/3 tsp of semolina into the middle of the floor and count how many secs it takes to turn black. 2 secs =too hot, 3 secs = just right, 4 secs = not hot enough. With a fire on the side, decent underfloor insulation you should be able to crank out 2 min pizzas for at least an hour and a half without having to retire. If your oven is big enough the fire can be alternated from left to right every 45 mins or so to keep the floor recharged.

Regarding dome height for a neapolitan 800mm diameter oven, I really don't know. The hemisphere is a very good all round performer for cooking and structural integrity of the dome, but for a specific neapolitan pizza oven of 800mm I'd be guessing a height of around 300mm would work pretty well.

[sergetania]

No idea about biscotto but sounds expensive Also, why do I need to heat it to 1000F when pizza is cooked at 900F in 90 sec? Also, measuring temps in a pizza oven is not an exact science. It is not even necessary to make good pizza like David implied. I do it because I am a computer guy and like numbers. Maybe someone else measuring temps at the same oven at the same time will come up with a different reading.

As for the FIRST pizza, I solved the problem by not making the first pizza. I heat up the oven, move the fire to the side and let the oven settle for probably 30 minutes without baking a pizza. After skipping the first one, pizzas do not burn anymore.

300mm as David suggested is very close to the height of my oven and it works great for me.

[Linuc]

Yes sergetania , it's quite expensive. About 60 USD (500 swedish crowns) per 40x40cm brick. I bought four, hence the 800 mm oven.

So today I casted the insulation board. 50 mm perlite/cement. I found it pretty hard finding the right consistency. I read that for every 10 part perlite you add 3 parts of water, but when I did that the perlite and cement stopped absorbing the water. The water remained at the bottom of the bucket. No idea why. I mixed by hand, first perlite+cement and then added water. For the first few buckets I went with the 10 part perlite and 3 parts water recipe, but since it didn't feel right I decreased the amount of water a little bit and that seemed better. No idea how this went. Quite nervous.

I did the casting in the basement and luckily I had tarpaulin under the form cause the form leaked a bit of water. My bad.

I put a fan in the room to speed up the process.

And yes, I made two seperate forms. One for the opening. Found it easier that way.

[david s]

Yes sergetania , it's quite expensive. About 60 USD (500 swedish crowns) per 40x40cm brick. I bought four, hence the 800 mm oven.

So today I casted the insulation board. 50 mm perlite/cement. I found it pretty hard finding the right consistency. I read that for every 10 part perlite you add 3 parts of water, but when I did that the perlite and cement stopped absorbing the water. The water remained at the bottom of the bucket. No idea why. I mixed by hand, first perlite+cement and then added water. For the first few buckets I went with the 10 part perlite and 3 parts water recipe, but since it didn't feel right I decreased the amount of water a little bit and that seemed better. No idea how this went. Quite nervous.

I did the casting in the basement and luckily I had tarpaulin under the form cause the form leaked a bit of water. My bad.

I put a fan in the room to speed up the process.

And yes, I made two seperate forms. One for the opening. Found it easier that way.

A 10:1 mix results in a very weak slab with insufficient strength for under floor insulation, it is recommended that you go with a 5:1 for under floor insulation, but over the dome which only needs to be firm enough to render against you can use the more insulate 10:1 mix. If I were in your position I'd be recasting that slab. (see attached table)
The 3 litres for every 10 of perlite is a bit of a rough guide as the finer grade of perlite requires more water and the more coarse grade requires less, as well as the moisture already in the dry perlite will vary. If water is pooling at the bottom of your barrow simply add a little more dry material in the same proportions. Also if you wait for 5 mins after mixing the perlite may absorb a little more water so when you wait and remix it's just right. If there is water in the bottom of the barrow it tends to wash the cement off the grains of perlite resulting in an inconsistent mix.

[sergetania]

But then your pizza will never burn! Please don't forget to report on that after baking.

I totally hated working with perlite. It was a disaster when the first few inches of the perlite I laid around the dome started to fall off. Check the pictures in my build so if that happens that's not a surprise. I overmixed it with an electric mixer too, and also ended up reducing the water by a lot. Hated it!

[david s]

But then your pizza will never burn! Please don't forget to report on that after baking.

I totally hated working with perlite. It was a disaster when the first few inches of the perlite I laid around the dome started to fall off. Check the pictures in my build so if that happens that's not a surprise. I overmixed it with an electric mixer too, and also ended up reducing the water by a lot. Hated it!

Yes, everyone hates the mix. The 5:1 mix is much easier to handle because it has more cement to hold the grains together, but more cement means less insulating capacity (see table). I find the 10:1 mix is about as lean as you can go and still have it workable. Two tricks I've found that help are firstly using a mix of 50/50 perlite and vermiculite and secondly, adding a handful of powdered clay for every litre of cement added. It gives the mix more stickiness which holds the grains together better.

Regarding the base burning, many regard the leoparding of the base as desirable, which imparts a slight bitterness to the crust.

[sergetania]

Many desperate people out there trying to justify burnt pizza. Leoparding and burnt are two different things if we are honest! Even charred and burnt are different but I have definitely tried passing burnt food as charred. Trying to convince myself, first of all, but I always knew, deep inside. But that's how you learn - you learn to cook great pizza by cooking bad pizza.

[david s]

“Many desperate people out there trying to justify burnt pizza. Leoparding and burnt are two different things if we are honest! ”

If we’re honest leoparding charring and burning are all the same, but different degrees of burning. The black spots on the bottom of of the pizza base (leoparding) are the beginning of burning.
Some folk are adamant that WFO pizza dough should never contain sugar or oil, both of which are browning agents and can promote burning. I have had excellent pizza from WFO cooks who don’t subscribe to this theory though.

[Linuc]

A 10:1 mix results in a very weak slab with insufficient strength for under floor insulation, it is recommended that you go with a 5:1 for under floor insulation, but over the dome which only needs to be firm enough to render against you can use the more insulate 10:1 mix. If I were in your position I'd be recasting that slab. (see attached table)
The 3 litres for every 10 of perlite is a bit of a rough guide as the finer grade of perlite requires more water and the more coarse grade requires less, as well as the moisture already in the dry perlite will vary. If water is pooling at the bottom of your barrow simply add a little more dry material in the same proportions. Also if you wait for 5 mins after mixing the perlite may absorb a little more water so when you wait and remix it's just right. If there is water in the bottom of the barrow it tends to wash the cement off the grains of perlite resulting in an inconsistent mix.

Sorry, I was vague. I did go for the 5:1 mix but had 3 parts water for every 10 of perlite. In other words 1,5 water for every 5 perlite. But I found that to much so after I while I changed to about 1,2 water for every 5 perlite. Still think I need to recast the slab?

[Petter]

Cover it for a week, remove the mold and let it dry. Don't lift it wet. It is fragile and any additional weight (from the exess water) is a risk. This big and only 50 mm thick is really pushing limits of what is manageble.

Slide it onto a plywood sheet when moving.

Lycka till!

[Petter]

If you se a big thick pool if cement in the bottom of your cast after removal, then maybe yes.

Give it a feel. Compacted perlite alone without any cement can hold the pressure of five ovens on top of eachother without breaking. The weak part is the edge, which may crumble. As long as the slab is contained with something that provides support, it is sufficiently strong.

The tiles at the bottom does not provide a continuous support. This nessecitates the need of a good homogeneous cast. Otherwise, there is a great risk of perlcrete crumble.