Flue cement keeps cracking

[Gazzt]

Has anyone got any advice on how to stop flue cement cracking. I used regin 1200 degrees cement but cracked.

 

[ShaunCorbs]

edt dopey me

you on about fire cement

normally due to air bubbles or movement in the flue

 

[Gazzt]

I mean sealing the flue to the boiler, i know some poeple use high temp silicone. I have used fire cement but it keeps cracking.

 

[Last Plumber]

I normally press it in well and then wet the surface a bit to smooth it over and let it dry before applying any heat.

 

[Best]

Wet the surface or cord that you are putting the fire cement against before you start. Maybe mix some water with fire cement also, but not much, - just enough to make it slightly damp. Too much water will also cause bubbles or contraction.
Put oil boiler on for half a minute, just enough to make flue warm and switch off and leave to harden. (if solid fuel, then just a tiny fire started if possible)
Try the special fire cement that comes in tubes for gun. It has flexibility and although expensive, it is very handy.
If you are sealing any flues on boilers or areas that will only get temperatures of 300 degrees, or less, then use heat resist silicone. Ordinary silicone can usually take 200 degrees, but check the MIs

 

[Gazzt]

Thanks for the replys will redo it using your advice.

 

[Best]

What sort of boiler and heat will the fire cement be for?

 

[Gazzt]

Its a 20 year old firebird with a 5 inch flue.

 

[Gazzt]

The flue gas temp 275 to 300 deg on analyser so i thought silicone my perish quickly so i thought the 1200 degree regin fire cement would be the answer.

 

[Best]

It isn't too hot really, but sort of at the limit of heat resist silicone in my opinion. I do find it disintegrates on high heat areas eventually. But will last forever on lower heat.

 

[Gazzt]

Cheers for your input

 

[SimonG]

Last I heard it was no fire cement on flues.