Ceramic insulation cloth

[Irv Mac Dowell]

I will be covering my 90 this week with 2 layers of concrete and ceramic cloth. I'm going to end up with a stucco-covered dome oven. My question regards the refractory cement/cloth combination. Would it be better to drape the cloth over the dome and then slather on the cement? Or can the cloth be pressed into wet ref. concrete, the way one might treat fiberglass cloth and resin?

Thanks.

Best regards,

Irv

[nissanneill]

Re: Ceramic insulation cloth

Irv.
My 40" Pompeii was covered with a themal blanket, tacked in place with long galvanised clouts (nails with large flat heads) just enough to hold without compressing it. I then wrapped it carefilly with chicken wire and then had to establish a way of getting the vermiculite cement to stick.
Rather than go through explaining the only way that i found is for you to see it at:

http://www.fornobravo.com/forum/f21/...-4-a-2045.html

permalink #8

All the best.

Neill

[dmun]

Re: Ceramic insulation cloth

The insulating blanket is pretty heavy and dense, it won't stick to a layer of refractory mortar very well. You are going to want that layer to dry out pretty well, so it retains a uniform thickness, before you try to mess with the blanket.

The insulation is pretty moldable, however, and tends to stay, at least temporarily, where you put it. The problem is that it's not dome-shaped, there will be overlapping corners that will be a problem with getting your stucco layer smooth.

Most makers have either overlaid it with a few inches of vermiculite concrete, to get a smooth surface for the stucco, or if they are going with blanket insulation alone, to cover it with a layer of hardware cloth or chicken wire to form an armature for the stucco first coat.

There's no reason to put refractory concrete on top of the blanket. That's not a high-temperature area.

[Irv Mac Dowell]

Re: Ceramic insulation cloth

Thanks for the replies. It's beginning to make sense. Does the layer of concrete over the igloo shaped rebar/lath have to be mixed with Perlite?


Best regards,
Irv

[nissanneill]

Re: Ceramic insulation cloth

It most certainly does as the layers (there will need to be at least 3 inches thick) which act to insulate the dome and keep the heat in.
I found it very difficult to put on more than an inch at a time.

Neill

[Irv Mac Dowell]

Re: Ceramic insulation cloth

Still a bit fuzzy on this. Doesn't the 3 inches of ceramic cloth preclude the need for additional insulation in the dome/igloo shaping concrete?

Also, the suggestion in the instructions for using pencil rebar is a good one. Only trouble is- no one in my area, or even close, carries any rebar smaller than 3/8. Is there some other heavy wire that would work for the initial dome shape?

Irv

[dmun]

Re: Ceramic insulation cloth

No, with three inches of blanket you do not need additional insulation.

Pencil rebar? Sounds great. Never heard of it.

[gjbingham]

Re: Ceramic insulation cloth

I think 3/8ths is the pencil rebar. There's none smaller that i know of.

Dmun's correct on the insulation thickness for blankets. (never been wrong!)

Expanded metal lath or chicken wire will suit your needs for final shaping of the dome. Be sure to leave room for whatever thickness of perlcrete you're planning for, inside the wire. The wire holds it in place. It will not stick outside the wire well at all.

[Irv Mac Dowell]

Re: Ceramic insulation cloth

I must be more dense than I thought. My guess at the diameter of pencil rebar comes from page 34 of the Forno Bravo instruction book that says, "Drill 1/4" holes around the perimeter of the oven hearth..." "Insert pieces of pencil rebar in the holes, and bend them to the desired igloo shape." Since it would be difficult to insert 3/8 rebar into a 1/4" hole, I assumed. I guess the instructions are wrong, or at least incomplete.

I'm still not clear (hence my thoughts on density) about the perlcrete. If I understand you correctly, one says I don't need it over 3" of cloth. The other says use perlcrete. If I decide to add the perlcrete, do I sort of force it through the mesh dome shape that I've established, and then use stucco over that as a finish coat? Pictures in the instructions are not clear.

Again, thanks for the help.

Irv

[arevalo53anos]

Re: Ceramic insulation cloth

Irv:

I have used fiberglass in place of ceramic blanket (this last being better, of course, however more expensive) and a mix of vermiculite / cement in place of the perlite.
My oven is near of five years old and it is maintaining heat as the first times.
Despite the different materials, the technics to work with them are similar.
You could see at http://www.fornobravo.com/forum/f7/w...hase-3941.html

Luis

[Irv Mac Dowell]

Re: Ceramic insulation cloth

I finished the ceramic blanket covering today and covered it with chicken wire, but the surface is so irregular, with many gaps between the wire and blanket, that I can't imagine that the stucco will stick sufficiently well to yield a smooth surface. What would you think of a layer of vermiculite and portland cement as a base for two layers of colored stucco? I assume that the concrete will fall behind the wire and harden there, thus filling the gaps.

Thanks.

irv

[gjbingham]

Re: Ceramic insulation cloth

You waht a gap between the chicken wire and your blanket equal to the amount of vermicrete you're planning for. Vermiculite/concrete will not stay put outside this lattice. If you need two inches of vermicrete, leave a two inch gap between the chicken wire and the blanket.

Stucco sticks nicely to that vermicrete layer without additional help - right at the vermicrete/chicken wire interface. Smash into place. It sticks well.