Fire Cement v. Intumescent Acrylic Sealant. Flue to Collar.

arco_iris · Post by **arco_iris** » Tue Dec 15, 2020 8:22 pm

Very heavy, Cast Iron single flue to collar joint on top of 13kw woodburner.

Installation notes, Building Regs., pdfs downloaded, & youtube videos all say fire cement, but they're all a few years old.

Is there any reason why I can't use copious amounts of Intumescent Acrylic Sealant, 4 hour retardant plus the cartridge says the deeper the fill, the longer the resistance - in a collar this is going to be 40 - 50mm.

Not a question of cost, just that I need the sealant elsewhere & it seems a bit daft buying 2kg of cement just to use a fraction of it in the collar.

Thanks in advance.

ayjay · Post by **ayjay** » Tue Dec 15, 2020 8:38 pm

Honest answer, I don't know.

My thoughts though, are that the Intumescent Acrylic Sealant is just that, it's a fireproof sealant usually used at doorways etc to help prevent the spread of house-fires.

It may have a 4 hour survival, but what about long term, can it survive 4 hours exposure (or more) day after day?

arco_iris · Post by **arco_iris** » Tue Dec 15, 2020 9:37 pm

Good point. Thanks Ayjay.

Fire Cement sets rock hard, don't know what intumescent sealant does, but by the nature of 'sealants' they usually stay soft/flexible, don't they.

Was more wondering if the regs. are out of date, fire cement superceded by more modern materials, any HETAS people looking in.....

But it's my own house, (replacing like for like stove, nothing else changes) if sealant looks like failing easy enough to revert to cement at a later date.

So, question then, does acrylic intumescent sealant set rock hard with heat?

Someone-Else · Post by **Someone-Else** » Tue Dec 15, 2020 9:56 pm

arco_iris wrote: ↑Tue Dec 15, 2020 9:37 pmSo, question then, does acrylic intumescent sealant set rock hard with heat?

I would not recommend it.

Intumescent strip is what fire doors have, (its also available as a sealant) it remains flexible until there is a fire, in which case it expands and seals the door, it's not meant to be used as a permanent seal. It has only been tested and g'teed for 4 hours, which is fine if its to stop the spread of fire, but not for what you want.

arco_iris · Post by **arco_iris** » Wed Dec 16, 2020 8:45 am

Someone-Else wrote: ↑Tue Dec 15, 2020 9:56 pm Intumescent strip is what fire doors have, (its also available as a sealant) it remains flexible until there is a fire, in which case it expands and seals the door, it's not meant to be used as a permanent seal. It has only been tested and g'teed for 4 hours, which is fine if its to stop the spread of fire, but not for what you want.

Was not referring to intumescent strip on a fire door but intumescent acrylic sealant cartridge.

Further research confirms not suitable anyway. Thanks both.

Razor · Post by **Razor** » Wed Dec 16, 2020 1:03 pm

For anyone else reading this don't even think about it. Intumescent sealant is meant to be a one use emergency thing to contain fire or smoke. It would degrade really quickly in the application you're talking about.

Fire cement is definitely what you need

aeromech3 · Post by **aeromech3** » Wed Dec 16, 2020 3:49 pm

arco_iris wrote: ↑Tue Dec 15, 2020 8:22 pm Not a question of cost, just that I need the sealant elsewhere & it seems a bit daft buying 2kg of cement just to use a fraction of it in the collar.Thanks in advance.

Last time I bought some it was in a plastic tub.