suitable materials for filling gap around flue

[ambrosia]

Doing landlords i frequently come across flues with large gaps around them where they pass through walls that have never been filled in,
sometimes theres those rubber collars hidding the hole, but often you can look along the flue to daylight
(occasionally on bigger holes i see newspaper stuffed in by the tenant to stop draughts)

I dont why hole are so common, maybe some engineers meant to return to make good others are just plain lazy. needless to say its not really exceptable


to make good, with a small gap i've seen engineers use silicon to seal the hole and on larger gaps expanding foam

logically both would work, both can be purchased with heat resistant qualities, both are hard wearing and should last, and both should stop any air flow or transfer of unwanted gases

however in my gas book it says flues should be sealed with sand and cement, with no mention of any other suitable products.
Is foam and silicon a no no

 

[dave1]

I work for a HA and I'd say at least 50% flues are not made good it's ridiculous poor workmanship in my opinion. I'd cement them in... However have seen them made good with silicone and other products.

 

[Barry98]

Don't some books read a suitable material ? Yet another grey area in our trade lets not forget the outer flue if twin lined is only air flow in

 

[stokecity]

when i do istalls i stitch drill quite tight, soim notgoin gooutand buy a bag of sand and cement which ive then ot to carry round with me, when i can just use some heat resistand silicone which ive already goton the van

 

[stokecity]

typing in the dark so there sum mistakes in that last post haha

 

[tamz]

typing in the dark so there sum mistakes in that last post haha

Are you under the stairs? Sun still shining here but just going down.

 

[GrahamM]

Are you under the stairs? Sun still shining here but just going down.

Or hiding from the wife in the cupboard? Maybe he short of her housekeeping money for the week.😀

 

[grahamgas]

when i do istalls i stitch drill quite tight, soim notgoin gooutand buy a bag of sand and cement which ive then ot to carry round with me, when i can just use some heat resistand silicone which ive already goton the van

Who still stitch drills in this day and age?

The last time that I had to was on an install in Paulsgrove. cast concrete walls as hard as nails, with rebar. Core wouldnt even touch it.

As to the OP, I have used all methods exp. foam can be wasteful if using tins, as it would have to be a big gap to use a whole tin.

Sand and cement is my preference.

But then how do you seal the outside wall on a sixth floor install, when flue has been put in from the inside?

 

[tamz]

I took the baby kango to one on monday. Bloody nofines and i wasn't loosing the tooth off a £100 core bit drilling it.

 

[AWheating]

I work for a HA and I'd say at least 50% flues are not made good it's ridiculous poor workmanship in my opinion. I'd cement them in... However have seen them made good with silicone and other products.

i worked on simular work, in the end i went around and disconnected and labeled them, gave the tenant the comapny phone number and told them to phone and complain that the boiler is dangerous and has been turned off. Once the HA get wind of the compliants they will start to get patched or the work passed to another company......... give them a quote 😉

 

[AWheating]

an unpatched flue (std flue) is AR unless allowed by the manufacture imo. either patch it or turn off and quote for the patching.

 

[neily01]

speaking to our local vokera breakdown engineer about this very subject and he use fire cement to seal around flues if not done and the gap is not to big. i thought not a bad idea quick and easy, [messey stuff] but not to sure how it will react with the lack of heat?

 

[REDSAW]

i use pre mixed tile adhesive if i have some scrags left over from a bathroom job, keep it in a tub and last for ages. takes 2 mins and sticks like ......,sure its heat proof?.

 

[tamz]

speaking to our local vokera breakdown engineer about this very subject and he use fire cement to seal around flues if not done and the gap is not to big. i thought not a bad idea quick and easy, [messey stuff] but not to sure how it will react with the lack of heat?

It still hardens, just takes longer.

 

[stevetheplumber]

when we was busy we carried a bag of sand and one of cement

 

[MK_Swans]

Expanding form (I used the gun grade) keeps for ages and no mess and you can cut it back/sand it once cured.

 

[Barry98]

when we was busy we carried a bag of sand and one of cement

Bag of ready mix ,

 

[Backboiler]

I do lots of landlord checks and I'm alarmed by the quantity of wobbly flues/chimney's that are left by the installer. They have drilled a 127mm core, stuck the flue through the hole and left it! It's for that reason I carry a old fashioned sweet tub full of readymix mortar and I seal it at no extra charge. Peace of mind.

 

[ambrosia]

and I seal it at no extra charge. Peace of mind

WHAT!!!
really :angelsad2:

i must be over charging, i normally make that into an hours work and hand out a £70 bill plus parking

 

[stevetheplumber]

Bag of ready mix ,

works out bloody exspensive that way about a fiver for 100kg of sand and cement fiver for 10kg redimix

 

[Backboiler]

WHAT!!!
really :angelsad2:

i must be over charging, i normally make that into an hours work and hand out a £70 bill plus parking

Yeah. It take 10 mins max. That probably why I do loads of Landlord checks

 

[neily01]

thanks for that, sounds like its worth having a tub in the van

 

[Mickyplumb]

As someone said, expanding foam but need to make sure it's the fire stop type

 

[gasmanrob]

if your using expanding foam make sure the boilers turned off!

A bloke in sidcup was told his boiler wasn't up to standards last year as his flue was not sealed through the void, so being a builder he thought i know ill whack some expanding foam in that. boiler fired up as he was squirting it in, the fumes from it got sucked in the intake and blew the boiler to bits case and combustion box. (was a profile) and the fella suffered 3rd degree burn as the can blew up in his hands.

Wouldn't use it myself been to a few jobs where someone had put to much in and as a result it squeezed on the flue causing it to crush a little and pull it out of its seal. why risk that for the sake of a bit of sand and cement. i keep a mortar gun on the van so if i cant get a trowel in a can load that up and pretty much inject it in.

 

[mfgs]

Bag of ready mix ,

I have always got a bag of ready mix in the van.

 

[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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