I require information on the establishment of the insulating hearth for the wood fired oven. There appears to be some divergence of opinion as to the most effective way to achieve success with this. Firstly is it necessary to pour a two part slab for a domestic oven and if so, is it better to pour the vermiculite layer first or last?
Welcome aboard John,
You have put your finger on one aspect of installation that has changed over the past couple of years. We definitely recommend putting the cooking floor directly on the insulating layer; and if you want more mass, which is not necessary for most installations, you should build the Island hearth, which puts an island of mass directly under the cooking floor, and surrounded by insulating concrete.
As a data point, The Fire Within's catering oven, that is consistently baking over 60+ pizzas an hour for hours at a time, has the cooking floor directly on the insulating layer.
When we first published our plans, there was some thought that putting the concrete layer on top of the vermiculite insulating layer would improve heat holding capacity, without negatively impacting heat up time and (most importantly) cooking floor re-charge efficiency. Looking back, that wasn't a good design trade-off.
The concrete on top design was counter to the instructions from Forno Bravo's two oven producers, who specifically recommend putting the cooking floor directly on the insulating layer. But being a constant experimenter, I wanted to see if we could improve on the "traditional" method. With more experience, we have learned that the advantage of better heat holding is not worth the downside of having a hearth that does not respond as efficiently to the fire in the oven.
The installation guides for all the Forno Bravo ovens now all describe the insulating layer on top.
One last thing. We just located a great under oven insulator, which is a 2" board that is more efficient than 4" of vermiculite concrete. It's called Super Isol, and we are now selling it on the Forno Bravo Store. You install the oven directly on that layer, and avoid having to mix vermiculite and portland, and pouring the insulating layer.
Sorry for any confusion -- I hope this is helpful.
Wood fired oven
James, thank you for the prompt reply and the valuable information.
island hearth diagram
Anyone direct me to a diagram of the island hearth?
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