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Sealing flue gap of 10mm with silicone?


Poppin

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Just took delivery of the new stove. It is designed for a 5 inch flue, and my plan was to install a 4.5 inch single wall flue with silicone and fire rope. 

 

As you can see from the pictures attached, the flue collar is a little larger than expected. The 4.5 inch flue will still fit and surround the internal hole of the stove, but the gap to fill all the way around is about 10mm. 

 

Will it still be acceptable to seal this with envirograf silicone and fire rope? If so, what order and procedure would you recommend? If not, would you recommend a reducer like this:

 

https://www.midlandchandlers.co.uk/products/ag-socket-adaptor-reducer-cast-iron-hf-462-m

 

Any help appreciated!

 

Also while I'm here, can anyone recommend a white or off-white enamled stove paint for the flue? Cannot find a thing 

 

 

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Just had a look at mine and the gap is almost as big as yours. I used fire-rope, its available in some quite big sizes, and then high temperature silicone.

I have found that fire cement cracks after a short time.

The silicone on mine is coming a bit unstuck so will likely need redoing before this winter, but its been on there for several years without problems.

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As others have said, fire rope and Envirograf, which will withstand up to 1200c. However, do make sure your fire rope seals all possibility of flame contact first before sealing the remaining gap with Envirograf. The instructions specifically mention that, if exposed to flame, Envirograf will burn with a barely noticeable flame.

Incidentally, Envirograf smooths very nicely to give an excellent finish to the top of the collar. I used clear, which blends perfectly with my flue once dressed with Stovax stove blacking.

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9 minutes ago, Sea Dog said:

As others have said, fire rope and Envirograf, which will withstand up to 1200c. However, do make sure your fire rope seals all possibility of flame contact first before sealing the remaining gap with Envirograf. The instructions specifically mention that, if exposed to flame, Envirograf will burn with a barely noticeable flame.

Incidentally, Envirograf smooths very nicely to give an excellent finish to the top of the collar. I used clear, which blends perfectly with my flue once dressed with Stovax stove blacking.

I think it flaunches off, according to @Tracy D'arth. Lovely word, flaunch. Apparently derived from flange. I recommend we have it as word of the week.

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49 minutes ago, Puffling said:

I think it flaunches off, according to @Tracy D'arth. Lovely word, flaunch. Apparently derived from flange. I recommend we have it as word of the week.

Very commonly used word especially with relation to chimneys. Often people use cement which is often wrong and should be lime mortar. 

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2 hours ago, Sea Dog said:

However, do make sure your fire rope seals all possibility of flame contact first before sealing the remaining gap with Envirograf. The instructions specifically mention that, if exposed to flame, Envirograf will burn with a barely noticeable flame.

 

Yes, stuff the gap with plenty of rope first so that it's reasonably solid, then seal with Envirograf. Don't put the silicone in first as someone suggested as it will burn so pointless.

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1 hour ago, Poppin said:

Thanks so much everyone! Would you use the same combination of rope followed by sealent for the gap between flue and roof collar? 

 

Yes. You need to seal the gap above the rope so that water vapour and combustion gases condensing on the inside of the chimney and dripping down can't penetrate and leak through the gap.

 

Your flue will expand as it gets hot so the rope and sealant create a flexible seal that can accommodate the expansion. Check the sealant in summer once you stop using the stove and reseal if required.

Edited by blackrose
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The flaunching is the sloping, water run off, finish to the top of a chimney stack around the pot or to the bottom of a manhole around the inlets and outlet.

Its an established building term.

 

I put a small amount of Envirograf in before the rope to glue it in place, probably not necessary.

Use of fire cement is the biggest cause of cracked collars on stoves I have found, its too hard and the expansion does the damage.

Its also the very devil to remove from the roof collar when you want the flue out. 

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3 hours ago, Tracy D'arth said:

 

Its also the very devil to remove from the roof collar when you want the flue out. 

I had to drill a succession of holes down through the cement until the bit hit the rope then join the holes up. Certainly got through a few drill bits.

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