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Old 04-08-2008, 01:07 AM
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Default insulating and rendering the flue?

Hi all,
How far up the flue should you carry the insulation and render / stucco? I left mine fairly flush with the dome (did not extend up at all) and noticed the stucco just couldn't handle the heat and cracked around the join. I think this will let water in if it does not get fixed so was thinking about wrapping the stainless flue with ceramic blanket, chicken wire and then rendering it up to the hat. Any thoughts?
Thanks in advance.
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Old 04-08-2008, 05:26 AM
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Default Re: insulating and rendering the flue?

Mieno,

There's really no need to wrap the stainless pipe in ceramic blanket any higher than about four inches above the anchor plate (the join is the hot spot). What your really want to do is build a chase (shape your choice) out of lathe wire, which you can then coat. The point of a chase is to build it so there is an air space of about two inches between the pipe and the wire. This allows for air circulation, and you won't get any cracking.

Jim
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Old 04-09-2008, 12:04 AM
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Default Re: insulating and rendering the flue?

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Originally Posted by CanuckJim View Post
Mieno,

There's really no need to wrap the stainless pipe in ceramic blanket any higher than about four inches above the anchor plate (the join is the hot spot). What your really want to do is build a chase (shape your choice) out of lathe wire, which you can then coat. The point of a chase is to build it so there is an air space of about two inches between the pipe and the wire. This allows for air circulation, and you won't get any cracking.

Jim
Thanks Jim. I think I understand what you mean with the chase but at the top of the chase the stucco will eventually meet the stainless pipe right? Won't it just crack at this join?
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Old 04-09-2008, 12:28 AM
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Default Re: insulating and rendering the flue?

I don't know if this will help at all, but I had small cracks where the cement-based stucco layer met the archway, due to the archway expanding when hot. But the next layer of acrylic paint seems to have filled them up and covered them nicely... What kind of outside layer have you put on the oven mieno?
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Old 04-09-2008, 04:50 AM
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Default Re: insulating and rendering the flue?

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Originally Posted by Frances View Post
I don't know if this will help at all, but I had small cracks where the cement-based stucco layer met the archway, due to the archway expanding when hot. But the next layer of acrylic paint seems to have filled them up and covered them nicely... What kind of outside layer have you put on the oven mieno?
Frances
It's a 3 coat render / stucco over chicken wire mesh. The final layer has an oxide colouring. I have not painted the outside. So the acrylic paint can handle the heat ok? Is it a special type of paint?
Thanks for your response.
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Old 04-09-2008, 06:39 AM
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Default Re: insulating and rendering the flue?

The paint is what the guy at the DIY recomended. Its acrylic and made for painting the outside of houses - that's all I know. But it goes on like corrector fluid and dries in a nice safe thick layer.


Actually, I'm guessing that if you pull the stucco up to the top of your chimney the join will be that much cooler than right at the vent, and maybe cracking won't be so much of an issue. Also if you put a roof on top, it would protect the edge of the chimney from getting wet and so even if cracks did appear they wouldn't get wet.

Jim, would you leave the gap between wire/stucco chase and the chimney at the top or close it up? Sounds as if you'd have to leave it open for the air to circulate, but you'd have to protect it very well against rain then.
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Old 04-09-2008, 07:05 AM
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Default Re: insulating and rendering the flue?

Frances, Mieno,

You're correct, Frances, the top of the flue will not get very hot at all. I'd close the chase at the top, sloping it for runoff all round. Depending on material, it will breathe sufficiently that closing it will not be a problem. The main thing you're doing is using the air as a passive insulator so any heat from the pipe is not transferred directly to the chase and coating, leading to cracking.

Jim
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Old 04-09-2008, 07:14 AM
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Default Re: insulating and rendering the flue?

I was thinking I would put chicken wire around mine. (its metal)
And then coat it with an inch or two of high heat mortar.

Then cover that with perlcrete followed by stucco...

I was hoping the mortar would hold heat and help with the draw, and the insulation would keep my fingers safe....

Any thoughts?
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