suitable materials for filling gap around flue

[AWheating]

does it say on expanding foam tubes it will have no reaction with metals and plastics?

 

[Barry98]

I can't see the point of foam your still going to need some cement outside for blow off , condensate if outside , flue if no collar so why not not mix a bit extra

 

[GrahamM]

I can't see the point of foam your still going to need some cement outside for blow off , condensate if outside , flue if no collar so why not not mix a bit extra

Exactly. And it is fireproof, weather proof, little shrinkage, cheap and only 5 mins to mix and apply.
Why would you use anything else?

 

[wheeto]

flue if no collar

I thought it was collar or no collar nowadays? ie it has to be sealed even if there's a plastic collar hiding the gap?

Or I may just have misunderstood you.

 

[Barry98]

I've always sealed it even with a collar to be honest I didn't know you couldn't , what I meant was evn if under the collar you use foam you still need cement to do prv condensate etc

 

[GrahamM]

Unless the manufacturer specifically says it is not required, to comply with BS5440 for room sealed appliance:
'The annular space between the flue assembly and surrounding structure shall be sealed.'

The collar is does a decorative item and does not give any support to the flue through the wall or seal the annulus as above.

Here is another way I look at it. The flue term must be 300mm from a ventilation opening. Is the flue hole not an opening?

 

[Pssst]

Havent read it all.

Unsealed flues are, IMHO at least AR.

It is not uncommon if the wind changes,for POC and/or unburned gas or gas /air mixes to re-enter the premises.

Many installers just slip the rubber flange over the outside but that isnt good enough. They do deform with weather,dont always seal well and can fall off.

 

[Backboiler]

I thought it was collar or no collar nowadays? ie it has to be sealed even if there's a plastic collar hiding the gap?

Or I may just have misunderstood you.

I remember on my inspection by GSR we went to a boiler I had installed. While doing a tightness test the inspector asked if I had sealed under the collar of the flue/chimney. "Of course I have" I replied and left it at that. I went inside the property for my LDF, when I returned to the meter the inspector was standing on a stool inspecting under the flue collar. He looked at me and said "just checking,well done"

 

[Pssst]

And did you then admonish him for not using a suitable means of access for inspection i.e a stool instead of a step ladder?

 

[Backboiler]

And did you then admonish him for not using a suitable means of access for inspection i.e a stool instead of a step ladder?

Sorry but I wondered if any bright spark would pick up on that. In fact it was my aluminum folding platform steps but it was easier to spell stool

 

[Billy Bob Bob]

right first of all if its unsealed its AR in particular push fit plastic flues commonly found on HE appliances if its not made good whats to stop that flue coming out of that bend if a fault develops such as explosive ignition?it has happened before and caused fatality's,not all will have a self tapper holding them together,secondly normal expanding foam is not deemed suitable,it must be the heat resistant type,thirdly how hard is it to carry sand and cement on the van?? if you find it not sealed sort it out and charge accordingly you are the last person there,the buck stops with you,thats no grey area thats black and white

 

[Dannypipe]

I carry a tub of fire cement. It's ready mixed and is under a fiver a tub. Plus it doesn't go off in the tub, but once applied it goes bullet hard within a few hours. I use gloves when squiding it in, and then trowel it off with a pointing trowel. Doesn't take long.

You can buy it from Screwfix for about £4.

 

[buckley plumb]

How to install a flue for a Greenstar boiler - YouTube

 

[Barry98]

No Nonsense Fire Cement 2kg | NoLinkingToThis

How many flues can you seal with a tub of that

 

[Dannypipe]

No Nonsense Fire Cement 2kg | NoLinkingToThis

How many flues can you seal with a tub of that

Yeah, that's exactly what I was talking about. I guessed the cost as I couldn't remember. You can do loads of flues with a tub like that. It lasts ages in the tub, and as I said, goes rock hard once set. Which by the way isn't that long.

 

[Barry98]

Might give it a whirl save carrying ready mix and time mixing

 

[neily01]

i posted fire cement 5 days ago, not a word on it. dannypipe mentions it and its a great idea! dans well stole my thunder!! lol

 

[Barry98]

Apologise fella I didn't see it

 

[Dannypipe]

Well sooooooooorry!! LOL! 😉

 

[ambrosia]

you used to get a strip of silver tape with a new flue which you were suposed to wrap around the flue to protect it from the concrete.
manufactures seem to have stopped supplying it these days

I rang gas safe on this issue, got some grumpy guy who didnt want to answer any questions or be helpful at all. however i did manage to get out of him before i was told to go away that sand and cement was the only suitable material

thanks for all you replies and I think i'll be ncs all those sealed with expanding foam seals i see on landlord inspections

 

[Dannypipe]

Most flues are stove enamelled, or painted. I think the tape you mention is for telescopic flues but I could be mistaken. You still get a strip of tape with a lot of them.

 

[kozak1968]

Silicon mastic does the job. Valliant say a suitable sealant. The outer flue is low temperature on condensing boilers so i personnally think this is o.k but somebody will prove me wrong......

 

[AWheating]

Silicon mastic does the job. Valliant say a suitable sealant. The outer flue is low temperature on condensing boilers so i personnally think this is o.k but somebody will prove me wrong......

as with any hole made through an internal or external wall it must be sealed with a material that keeps the specific fire rating of the wall, if the walls fire rating matches the mastic being used then it should be fine.

 

[TBServices]

I've used high temp silicone, but usually sand and cement. Only problem is after a while it can crack on small holes, seen loads that have done it. Might try the fire cement trick.


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