Fill gap round flue through ceiling - and hold

[Chris Green]

Our (professionally installed) wood/coal burning stove has a vertical

6" flue running straight up and through the ceiling.

We have a fan on the top of the flue which is needed occasionally when the wind is in certain directions, it's also very handy when lighting the fire.

There is a small gap around the flue's outer skin (it's twin-wall up there) and at certain fan speeds it rattles. The gap is probably five to ten mm or so.

So I'd like to fill the gap with something to stop it rattling and provide a little extra support for the flue. What should I use?

Are there any moderately high temperature silicone type sealants? It's not particularly hot up there being the outer skin of twin-wall but I guess it could be up to a hundred degrees or so. It would be best if the seal remains flexible, I don't think fire cement or some such would be suitable.

(it was installed 20 years or so ago so I can't really complain to the installers)

[nothanks]

A search for "heat resistant silicone" will find what you need

[Theo]

I had a tube of this:

mainly because it was neutral cure and high modulus, but it also goes up to

280C.

(never actually used it because I never needed it for what I got it for - the shelf life is 12 months and 7 years later I tried to use it and found it was solid).

Theo

[Andy Burns]

[Chris Green]

That looks perfect, thank you.

[alan_m]

Just check screwfix for flue or high temperature sealants - 250C to 300C operation.

I used one 25years ago to seal a flue into a metal plate to stop crap falling down the old chimney falling on/into the boiler. It was removed recently and 3 buckets of fine old mortar grit removed from behind the plate. The high temperature sealant was still in good condition.

[Brian]

For a gap that large, silicone may need a bit of ‘support’. While, due to the pipe being twin walled, it probably is that hot, I’d still use high temp silicone as others have suggested but would ‘stuff’ the gap with the special ‘string’ stuff design for sealing around flues etc. I think it is called fire proof string or some similar name. An old oven door seal would work, the metal mesh type, if you can find some.

[Animal]

Sand/cement would be my first call, of course a lot of it will fall out when applied. High temp, fire rated or intumescent silicone would also work. You can also get fire rated acrylic sealants.

[Colin Bignell]

Flexible ceramic fibre blanket would be my choice.

[Andrew]

Fibreglass rope is available in a variety of thicknesses from decent hardware stores, or agricultural outlets.

[Brian Gaff]

Yes what is that kind of flat woven stuff which is heat proof called, Used to see it a lot in the old days of solid fuel burners in houses with retro fitted flues and chimneys. Brian

[Rod Speed]

Brian Gaff [e-mail] wrote

Asbestos.