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Old 08-14-2011, 12:50 AM
Laborer
 
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Location: Thousand Oaks,CA
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Default Chimney sealing

Hi,

I would like some ideas on how to seal the chimney that is going through the cement board. I am still figuring out how to do the roof, but I think I am leaning towards mosaic tile. I would need a way to seal it so that it retains a "flat" look, like it does in the picture so that I could tile over it.

Thanks,

Scott D.
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  #2  
Old 08-14-2011, 11:59 AM
Journeyman
 
Join Date: May 2009
Location: Detroit
Posts: 400
Default Re: Chimney sealing

Is your pipe double wall or single wall? I think I recall you mentioning it being single wall elsewhere which would really hinder your ability to finish it like you want. Tiling right up to a hot pipe is asking for trouble. On that same note what are your plans to install the tile so it is water tight? I'm working through this same plan on my new oven to eventually get to a broken tile mosaic finish, but am going to go a much different route to get there after a lot of research.
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Old 08-14-2011, 07:53 PM
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Default Re: Chimney sealing

There is no way to effectively seal that joint around the flue, nor is there a way to prevent cracking at those edges. Sorry but that is the fact.

You will need to rely on a secondary barrier, and as I have told you before, you will have to tape and float the joints with fiberglass tape and latex modified thinset. Then you need a liquid waterproofing membrane to coat the entire oven. For the flue, you will need counter flashing and a way to allow moisture to escape.

Tiling the entire oven will only work if it is indoors. You have to have some sort of roofing that is able to be flashed.
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Old 08-14-2011, 10:02 PM
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Default Re: Chimney sealing

Tscarborough,

I was just seeing if anyone else had any other ideas. I really don't want to put a roof on it like a house. I just want it tiled. I have purchased the supplies for taping and also red guard for sealing. I am just stuck on the chimney. Does it make a difference that I am in Southern California and hardly get much rain here. I could cover the oven during the few rainy weeks we get. Can I put refractory mortar around the chimney and tile over that? Would it help for me to purchase a double wall pipe? Would that give me more options?

Thanks,

Scott D.
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Old 08-15-2011, 12:46 AM
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Default Re: Chimney sealing

Scott, I have been down this road several times with my oven and can agree with Ts that it is virtually impossible to seal the area around the flue pipe and not have cracking in your tile mortar. You can seal it, how long it will last is anyones guess. A red Hi temp silicone (I bought mine from a refractory store on ebay) is your best bet (good for around 700F if I am not mistaken.

Here is my story, I'm sorry if I become long winded, but here goes.

My oven started out as a typical Pompeii brick oven, brick entry, and flew base. I use double walled DuraVent for my pipe. The origianl finish consisted of 2" blanket, the chicken wire covered in 2 1/2" of perlcrete, with a 1/2" shell of Heatstop 50 to give me a smooth service for my mosaic tiles. Tile mortar, right uo to the flu pipe. this stayed cracked almost constantly for 2 1/2 yrs with multiple patches . I tried one fibrous refractrory caulk which didn't hold up. Then one day after 2 weeks of freakish horizontal rain my entire oven became saturated and was actually weeping water out of the hearth.
My solution was to reface the entire oven with something no one else had tried, and most believe will let me down at some point...I layed down another 1" blanket over the old tile finish and then covered that with a pond liner from Lowes that I had cut to fit perfectly. then surface bonding cement , them polished river pebbles set in fortified thinset. Around the flue I had already tried everything I could think of so I resorted to buying a tube of the hi temp red silicone. Fortunetly. adding another 2-3 inches of mass had raised the junction point above what is visible from stand in front of the oven. The bright red silicone is not visible, but has been VERY effective. Its been 1 1/2 yrs since my facelift and so far, so good, No issues around the pipe anymore and I do not believe the pond liner has been affected from what little heat it receives . I was told it would shrink up from the heat causing new problems. I guess the fact that it went overtop of an already finished and well insulated oven has made a difference. So far, no water in the oven, no cracking of any mortar of the river pebbles, and the flue pipe is still sealed nicely. Another note, I originally had several nice cracks develope in the mortar of the mosaic tile that I could not seem to get rid of. Covering with all of the above mentioned new stuff and then topping with the river pebbles seems to have stopped that. my out shel actually seems to be water tight, and not effected by any thermal shock.

Just like you, I had no desire to build a house around mine, just wouldn't fit my vision.
My advise would be to get some hi temp red silicone and also get double walled flue pipe. single wall will just get way too hot for anything to seal it. Make sure you are very well insulated, hopfully you will get lucky and have no cracks anywhere in the mortar.

RT
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Old 08-15-2011, 02:29 AM
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Default Re: Chimney sealing

[QUOTE=Tscarborough;119050]There is no way to effectively seal that joint around the flue, nor is there a way to prevent cracking at those edges. Sorry but that is the fact.

No it is not.

I developed a workable solution to this problem, that has proved to be effective. I have used a vermicrete mixture around the base of the flue about 15 mm thick, outside of which is a stucco/render layer. At the top of the stucco layer I have a terracotta flange, which finishes it off neatly. None of these are in contact with the flue pipe, so expansion and excessive heat do not create any cracks around this area. On top of the flange I have a terracotta seal which is sealed against the flue pipe with high temp silicon.This system also allows the insulation layer breathe to the atmosphere reducing steam pressure between the inner and outer domes.

Last edited by david s; 08-15-2011 at 02:39 AM.
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Old 08-15-2011, 02:59 AM
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Default Re: Chimney sealing

Scott,
You could try some high temp silicon between the pipe and the cement sheet. Here is a pic to show how I solved this problem.
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Old 08-15-2011, 03:24 AM
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Default Re: Chimney sealing

Quote:
Originally Posted by david s View Post
This system also allows the insulation layer breathe to the atmosphere reducing steam pressure between the inner and outer domes.
You have a leak?
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Old 08-15-2011, 04:06 AM
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Default Re: Chimney sealing

No, no leaks, but when an igloo oven is out in the weather some water inevitably gets in, either through the entry with driving rain, or simply the porous refractory absorbing moisture from 100% humidity. Up here in the tropics it's not that unusual to get downpours of 6-8" at a time, or rain every day for a couple of months. Some water always gets in and the insulation layer gets wet. When you start driving it out with fire it only travels to the outside away from the fire not back to the inside of the dome. It therefore needs an escape route.
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Old 08-15-2011, 06:26 AM
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Default Re: Chimney sealing

David S, you also have double wall flue, unlike Scott D. You also do not have a house on your oven as does Scott D. The high temp silicone will probably not take the temps on the single wall pipe, and when it fails, he has a large amount of insulation to get soaked and no good way for it to escape.
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