Cement for woodburner/stack connection

When we got the woodburner put in five years ago, they threw in a tub of that KOS fire cement to seal the join between the stove and the stove pipe. Feeling that the gap there now needed sealing up, I dug out the tub only to find it's gone off in the meantime.

Another tub is cheap but I recall that the stuff tends to crack and fall away fairly quickly, and even the black-coloured stuff goes grey once it's been there a while.

What do other wood-burner owners use?

Reply to
Tim Streater
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Nothing :) Probably wrong but there you are.

Like you I found that the 'cement' cracked and broke away as there there was no trace of smoke I just left it.

Reply to
Mark Allread

Stove to pipe junction may not be that important if you have a decent chimney because of the "draw". Obviously, any sign of smoke or smell needs fixing because of possible CO.

Periodically I have to re-seal side panels to the "lid" because air leaks here mean you can't shut the fire down completely, at least if it is fairly full of dry wood.

Reply to
newshound

I should have said, I've used KOS or whatever the local hardware store have in stock. Woodburners can run a bit hot for silicone, the best stuff lasts to about 325 C iirc.

Reply to
newshound

It happens that newshound formulated :

Not much help, but you can get a replacement for asbestos string - could you perhaps pack the joint with that plus the KOS?

Reply to
Harry Bloomfield

Actually that's a thought. A CO detector was also installed, I should probably check its battery. But yes, the possibility of CO is what was worrying me a bit.

The draw should be good as we had the chimney properly lined and insulated at the time.

Reply to
Tim Streater

Yes, I should have clarified that a CO detector is in the room also as well as a very good draw.

Reply to
Mark Allread

I just checked our CO detector, test button worked OK. It's a FireAngel

7-year model so it's good for a couple more years. I also bought some more paste and applied that today. Will see how that goes.
Reply to
Tim Streater

KOS cement is basically a mix of sodium silicate (waterglass) and mineral fillers. The say it contains thermosetting resins, which I doubt, unless you call sodium silicate a thermosetting resin, and for 'cures' read 'dries out'. The sodium silicate won't react with the mineral filler until it reaches red heat. Something almost identical is made by Purimachos (KOS may even be Purimachos renamed/rebranded), and the Co. I worked for used to supply some of the filler. I guess the reason it cracks in applications such as yours is the repeated heating and cooling of the flue pipe, resulting in expansion and contraction, not matched by the cement. Best suited to firebrick.

Reply to
Chris Hogg

In fact that is the stuff I got today.

Reply to
Tim Streater

Normally ours has a good draw but not the other week. Weather was

*very* still and had been quite cold. On lighting the fire there was a little bit of smoke spillage into the room but nothing excessive or abnormal. Closed the doors leaving a small gap as normal to draw the fire for the first few minutes. It didn't really draw, thin smoke started to come into room, closed doors. Opened under grate vents, not a lot happened, Smoke started to come out of airwash vents, closed air wash, opened window and outside door on opposite side of house. Visibilty started to reduce in room. More smoke, thick heavy smoke, started to ooze from every orfice of the stove(*). Decided that the only course of action left was to open stove and stop the smoldering. Visibilty much reduced in room, bear in mind window open and cross draught (ha!) from open exterior door.

I think there must have been cold "plug" of air in the top of the chimney, that was too heavy for the fire to lift up and out. Used hot air gun to blow hot/warm air up the chimney for a few minutes, re built and lit fire no problems... B-)

(*) Wish I'd taken a photo but was a little busy at the time.

Reply to
Dave Liquorice

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