Best insulation layer order

[Audionatic]

I've picked-up Insulfrax 1" CF blanket, and FBX1900 board-type insulation for my barrel vault oven, so I can insulate while I finish my curing fires, then continue building the entry and chimney. I'm planning to use some enamel-coated copper wire to tie it loosely in place, in (3) 1" layers, then an additional 2" layer draped over the top of the dome. I'm planning to use the board to enclose the whole thing, with self-adhesive foil tape to hold the corners and seams together before I build a dog house-type weather enclosure around the whole thing. Will likely also dump vermiculite into the weather enclosure, over the FBX1900 board. My question is this; does it make any sense to put the board on first, then wrap that with the blanket? Which order will best contain the heat? Does anyone have a suggestion for best way to even temporarily fasten or adhere the board insulation to the home brew refractory cladding? Photo and FBX1900 specs attached. Thanks!

[mrchipster]

Re: Best insulation layer order

Do you have any insulation under your oven floor or under where your oven walls meet your supporting slab?

Now to your question. I assume you are adding the board to the vertical flat surfaces and the blanket over the curved surfaces.

Prior to building the house over the oven you should not require insulation, because if it rains the insulation will get wet.

Build your house,
Enclose the sides
Place the board against the vertical walls and backfill with vermiculite. The vermiculite will hold the board in place.
Cover the curved dome with blankets and put on your roof sheathing.
Fill the rest of the house with vermiculite. And you will be very well insulated from the sides and top.

I am concerned about your oven walls as it looks like they are placed directly on the supporting slab. And if they are you will lose considerable heat into the floor.

[Audionatic]

Re: Best insulation layer order

I'm trying hard to get the insulation done right on my build, Chip. It is almost fully enveloped. What you see in the photo, from the front storage opening in the base, up, is: 7" structural slab with double mat of rebar, then 6" vermicrete hearth base, then 4" FBX1900 insulation board (2x2"), then firebrick on edge as the hearth. There's a 1" layer of board wrapping the hearth fire brick outer edge all around, then the whole thing is clad in home-brew refractory to approx. 1.5" on the sides, and approx. 3" over the top. The board is pretty cheap. If I wanted to use blanket all around, and enclose with the board, is there a reason not to? I know we don't want to compress the blanket or it loses R. Cost is a factor, of course, but that aside, is there a best practice for the order of things? Once I get this baby hot, I want her to stay that way for a while. Thanks for the help.

[mrchipster]

Re: Best insulation layer order

The reason to not use board on curved surfaces is that it does not curve. Sounds like you did a great job of insulating under the floor. I think if you follow what I said in my prior post you will be in great shape. After the insulation of the oven the next major heat looser is the door.