Filling around new flue

FlaatusGoat

Just replaced my flue. Unfortunately where I had to smash out the old sand and cement around the old flue, I've now got a pretty big gap around the new flue to fill. I've also got quite a big cavity between the inner wall and outer. Completely filling wall the cavity with more sand and cement would probably be a bit OTT, a huge amount would be required. Can I simply tuck some paper towel around the flue where it enters the wall, and use that to create a 'bridge' for sand and cement of the top, rather than completely filling in the whole cavity. Or am I asking for a fire if I do that....?

FreeBear

Gas flue ?

Expanding foam will do the job, and zero risk of fire. The outer wall is cooled by incoming air, and the exhaust gasses don't get that hot.

Flue for a wood burner ?

Fibreglass rope or fire cement - You'd need to leave a small gap between the mortar & flue to allow for expansion & movement. A steel or aluminium plate is often used to cover any ugly holes.

stuart45

45 Degree Wall Sleeve for 5 inch Twin Wall Flue — GR8 Fires
If it's for a wood burner you need a sleeve as well as a rope seal.

FlaatusGoat

I think I sort of overestimated the problem, the fire cement I bought had much better of gap filling properties than I anticipated. I slipped a bit of old brick and rubble in the gap too as to provide a bit of a back rest for the fire cement. I had thought of using expanding foam mind you, but I hear it's a bit of a problem if you ever need to remove the flue again...Sorted.

FreeBear

FlaatusGoat said: I had thought of using expanding foam mind you, but I hear it's a bit of a problem if you ever need to remove the flue again.

I wrapped a short length of heavy gauge plastic round my (gas) flue before filling the gap with expanding foam. The gap was minimal (at most ~6mm), and the plastic will allow for the flue to be pulled out should the need every arise.