1" of Thermal Mass VS. 1" of Insulation

[RTflorida]

Re: 1" of Thermal Mass VS. 1" of Insulation

The type N is very sticky stuff, CJ recommended it when I was doing my weather seal coat before tiling. As Jim says - it is great stuff for vertical surfaces, stays in place with no sagging.

[CanuckJim]

Re: 1" of Thermal Mass VS. 1" of Insulation

James,

My understanding has always been that lime is used for added workability and stickiness. That's why I often use Type N with Lime (says that on the bag) when working on outdoor vertical surfaces.

Jim

[james]

Re: 1" of Thermal Mass VS. 1" of Insulation

I hope our pro masons can help out, but my understanding is that lime is for workability, not heat resistance -- which comes from the fireclay.

Is that right?
James

[asudavew]

Re: 1" of Thermal Mass VS. 1" of Insulation

Hey James,

Thanks for the info.

I will probably add a bit to the outside, but do I really need the lime in the mix?

I hate that stuff.

I made one small batch without it, and it seemed to work fine.
I actually couldn't tell the difference.

[james]

Re: 1" of Thermal Mass VS. 1" of Insulation

I would put adding thin coating in the advisable category. Definitely nothing thick or heavy. It does not take a lot of time, or material -- and I can't think of a negative.

You will patch up any potential cracks, or spots that might leak a little hot air or smoke.

Would our experiened builders agree with that?

James

[Frances]

Re: 1" of Thermal Mass VS. 1" of Insulation

You can still do a thin coat to seal up the oven, and give it a little structural integrity. You can just put it on with a trowel -- no heavy lifting.
James

So the cladding IS structurally necessary (or advisable)?

[james]

Re: 1" of Thermal Mass VS. 1" of Insulation

RefMix. It sets fast, which really helps. Make sure the oven is fully cooled down, and wet the area you are patching before you slop it on.
James

[Ken524]

Re: 1" of Thermal Mass VS. 1" of Insulation

Hi Ken,
I am going through the CDC phase right now, and I am patching the external cracks as I go. I am catching the hairline cracks each day as they appear, and so far, have kept them from getting bigger. We'll see.

Are you patching the external cracks with RefMix or some sort of high temp goo?

[james]

Re: 1" of Thermal Mass VS. 1" of Insulation

You can still do a thin coat to seal up the oven, and give it a little structural integrity. You can just put it on with a trowel -- no heavy lifting.
James

[asudavew]

Re: 1" of Thermal Mass VS. 1" of Insulation

Ken and Dave, the good news is that your ovens have a lot of mass and will still heat up quickly. You're there! Insulate the heck out of it, and you are ready to go.

That's great to hear James!

I was getting all worked up for a coat of mortar.... and lots of mixing!

WOOHOO!

Arch and entry way for me!

Thanks for the input everyone.

[james]

Re: 1" of Thermal Mass VS. 1" of Insulation

Hi Ken,

I am going through the CDC phase right now, and I am patching the external cracks as I go. I am catching the hairline cracks each day as they appear, and so far, have kept them from getting bigger. We'll see.

It turns out that 1" is the most widely produced thickness, so it is best to just run multiple layers. Overlap the seams, and it will work well.

Two boxes should give you three layers (just about). Go thicker on top, as there is more heat up there.

Have fun!
James

[Ken524]

Re: 1" of Thermal Mass VS. 1" of Insulation

Ken and Dave, the good news is that your ovens have a lot of mass and will still heat up quickly. You're there! Insulate the heck out of it, and you are ready to go.

Great news. Thanks for the advice James. The dome stays clean.

What I plan on doing is throwing on the blankets, curing, then building the enclosure. That way, in the event of Cracking During Curing (CDC), I'll be able to deal with it.

James, I think I can squeeze in 3" of blanket insulation. Does Insulfrax come 2" thick or only 1"? How far will a 50sqft roll go for a 42" dome?

Thanks

[james]

Re: 1" of Thermal Mass VS. 1" of Insulation

On the firebrick topic, the medium duty bricks have a slightly higher alumina content, so they are more heat resistent and more efficient at absorbing heat, but that does not translate into better heat retention. Conductivity works in both directions -- faster heat up and faster cool down. That is good for live fire cooking such as pizza, where you want your oven to recharge as efficienty as possible from the fire to maintain high heat. It has very little impact on retained heat cooking, such as bread and roasting.

I want to emphasize again how good these ovens are at retained heat cooking. You will be amazed and you will be able to bake more bread than your entire neighborhood will be able to eat! :-) You don't need more mass.

James

[james]

Re: 1" of Thermal Mass VS. 1" of Insulation

I definitely think that you should put that space into more Insulfrax. At a half brick your dome is already thicker than a commercial Italian pizzeria oven -- many of which bake bread every morning from retained heat.

Sometime I think that the Bread Builders book got everybody off on the wrong foot regarding oven thickness and mass. I remember building my barrel vault oven and thinking "cool, the walls are 9" thick; it must be better than those lighter ovens." Years of experience later, I figured out the different demands of a commercial bakery and a home chef.

Ken and Dave, the good news is that your ovens have a lot of mass and will still heat up quickly. You're there! Insulate the heck out of it, and you are ready to go.

[rlf5]

Re: 1" of Thermal Mass VS. 1" of Insulation

I think they have a higher aluminum content, but I'm not totally sure. The composition is different from light duty though. If you don't have any cracks I woudn't worry about it at all....or I'd just apply a thick coat to the joints to make sure.