Building a Valoriani FVR120 - is this setup OK?

[Dieter01]

I am just about ready to start building my WFO. I am not sure if I have the right amount (or ratio) of ceiling / floor mass and insulation. I have attached a file that shows my current plan... Anyy comments appreciated. I also have a few specific questions

1. Leca is a very cheap insulating material based on clay. λ = 0,079 to 0,12 W / mK (compared to Perlite which has a value of λ = 0,045 to 0,060 W / mK). Perlite is not readily available so thats why I am asking... Is Leca good enough or do I need to find Vermaculite or Perlite to fill the void around the oven?

2. The brick frame will be square and the dome of course circular. In the narrowest sections the distance from the dome to the brick wall is only 3-4". I plan to fill this section with multiple layers of the same insulating material that I will apply in two layers over the dome. Good enough or do I need a larger footprint to get more insulation in here?

3. Should I be concerned with the floor / ceiling mass and insulation ratios?

[Tscarborough]

The hearth buildup should be:

Oven floor
Just enough sand to level oven floor
Insulation
Concrete

Other than that, it looks good.  Provided you are using insulation blanket over the dome, that should be plenty left loose and fluffy.

[Dieter01]

Isn't it a bit risky to place the 10 floor elements directly on top of the sand?

Sand was recommended by the supplier of the oven and I believe was meant to have both some insulating properties and also minor heat retention properties. I added the Rockwool ground mat below myself in order to further improve the insulating properties.

If I drop the sand and use

Oven Floor (2")
Concrete (without vermaculite) (2")
Rockwool ground mat (2.8")
Concrete

Would that be preferred?

[Tscarborough]

Why do you want the extra mass in the floor?  That is the hardest part to heatsoak.  If you were building a bread oven that would work, but you only have 3" of refractory in the rest of the oven as is.

[Dieter01]

OK, I see your point. I was a bit scared that sand would work its way up through the floor but I guess gravity is on my side there... I am looking into sourcing some Super-Isol boards. If I can get a hold of something made of CalSil the setup would be something

Oven Floor (2")
Sprinkle of sand / clay or refractory mortar to level
Super-Isol (2")
Concrete.

(which I assume is the same as you suggested). I don't think the Rockwool ground mat that I previously mentioned has the compressive strength to place the oven directly on top of it but I will have to check that a bit closer. If it does that could be an alternative as well.

[widespreadpizza]

my 2 cents on sand.  if you have a perfectly flat surface to work with,  mine was perlcrete,  do not use the sand as you floor pieces should be very even in thickness.  I had laid out my floor and it was super flat.  then i went and did the sand thing and it ended up worse than it was before.  They have dropped the sand step in the Pompeii oven plans at forno bravo.  -Marc

[JConk007]

The Earthstones Model is 4" conc. 1 " lean cement ( 1 part cement 3 parts Sand ? cant remember very firm )  then the bakers tile.  No boards, blankets or compressed anything? ... ? Then fill the whole cavity with perlite with just a touch of cement to hold it all together. This was by far the hardest part of the build and equally inportant - leveleing the floor on the  lean cement. level and 2nd shot shows three layers  (can see in shelf) To this day 6 years later has not moved a millimeter.
Excuse  my mason work it was my 1st time doing this type of thing
John

[Dieter01]

Hello again! I ended up insulating a bit more than my initial post. I have 2" CalSil below the hearth and another 2" above the dome. The dome was first covered with an insulating ceramic blanket. I have also used about 1.3m3 (or 46 cubic feet) of perlite, the top of this reaches about 15-20" above the top of the dome. I borrowed some equipment from a company working with granite counter tops and used their sander to level the floor. I also placed a temperature probe below the floor so I can measure when the hearth is saturated with heat.

The only thing that is left now is to seal a 3/4" gap between the hot zone (front part of hearth and dome) and the decorative brick (ref last picture). I did use fire brick (the black one) here but not refractory cement to bind them. I also used some of the ceramic blanket in the gap. My hope is that this will reduce the heat loss to the front of the build. But how do I seal it? I have found a sealant rated to 350 deg C (660 deg F) that will remain plastic. I expect the hearth inside the oven to get a lot warmer than this though... So far I have not found a black or greyish compount that remains elastic and has a higher temperature rating. Suggestions?

[Tscarborough]

Looks very nice.

[Dieter01]

Thank you!

We fired it up for the first time fivedays ago. I light it back up every evening and have slowly increased the size of the flame. I have been anxious to see how the draft up the chimney is and so far its looking really good. I insulated it all the way but honestly thought it would be a waste. I guess I will never know what it would have been like with a different solution but at least for now I'm very happy I did, no smoke escapes out the front unless I am obstructing the airflow.

Heres a few more pictures...
The first shows the insulated pipe and the perlite inside the oven (ref also picture above prior to adding perlite). I'm happy that i had sufficient volume to cover the top of the oven well.
The second shows my first attempt logging the temperature (on day 4 I think it was). The logger on the right shows the temperature below the floor about 3" from the wall. I know, normal people don't care about stuff like this...
The last picture shows my "construction zone", hehe. Its great to be able to finally use it lightly, but at the same time there is a fair bit of work left. The good thing is that we are still enjoying that work and there is no rush to finish.