Insulation Board Help

[Pologuy9906]

Hi all. I have a few questions:
1. Do I need more than 1.5" of insulation board
2. What to use to level board on slab?
3. Should I go with a 5:1 verm:crete mix?

I'm trying to complete this.

[Larry P]

I'm hesitant to answer this question because with insulation, there is a point of diminishing returns. I don't know if anyone has done the research to know exactly where that is, but I can say that the Pompeii plans call for 2" of insulation, and 4" is considered state-of-the-art nowadays. Is 4" overkill? Maybe, but the cost of insulation, in terms of the entire project, is minimal enough that people will go overboard. There are plenty of ovens out there with poor insulation and they work just fine, although they won't hold residual heat as well as a well-insulated oven.

My oven placed the insulation directly on the slab (with a vapor barrier in between). I used a 50:50 mix of fireclay and sand between the insulation and floor bricks. This might not be necessary depending on how flat your insulation and bricks are.

The vermi-crete is something like 4-5x less efficient than ceramic board, so you could add additional insulation using that, but adding more ceramic board would be better.

[Pologuy9906]

Ok I'm going with 4.5" of fb under oven. For additional $150, it seems brainless not to do it.

[RandyJ]

I think you will be very happy with that decision. I have 4" and have great heat retention. For the small price it is worth it to me.

Randy

[Larry P]

Agreed, and I'll add, cooking with residual heat has been the unexpected surprise with our oven. It's been so good and so useful, my wife hasn't even whispered a concern about the cost of wood, which is out of character for her. The pattern looks like: 1 day after firing, 450ºF-500ºF, bake a Sicilian or Detroit-style pizza, day 2 350ºF normal baking, then it drops about 50ºF/day. Even on day 4 & 5 we're doing all-day crockpot meals and oven-dried tomatoes and fruit.

[RandyJ]

Yeah I have done a beer can chicken 2 days after I made pizza. I need to get better at useing my residual heat as I have a lot of it. I was at 631F 2 days out when I did the chicken. 7 pounder and it cooked in 1hr 15 min. Was super jucey and tasty.

Randy

[Pologuy9906]

Is there a premix mortar that's good?

[deejayoh]

Is there a premix mortar that's good?

plenty of builders use heat stop 50, but you will find it is very expensive compared to home brew