The Lemon Fool

I tend to spot a few polystyrene beads (4mm) around my boiler. They seem to be coming from where the plastic flue enters the wall. The hole for the flue is a few mm bigger than it would need to be to be snug.

Presumably these beads are the cavity wall insulation? Interesting, cos I always wondered what insulation (if any) I had in there.

Is it worth me fitting something to get a better seal? It has been in this condition for many years, so doubt it's causing a major problem.

MrFoolish wrote:I tend to spot a few polystyrene beads (4mm) around my boiler. They seem to be coming from where the plastic flue enters the wall. The hole for the flue is a few mm bigger than it would need to be to be snug.
Presumably these beads are the cavity wall insulation? Interesting, cos I always wondered what insulation (if any) I had in there.
Is it worth me fitting something to get a better seal? It has been in this condition for many years, so doubt it's causing a major problem.

Yes, unless you don't mind your insulation disappearing.

Just a normal sand/cement mix. Let it go off before heating.

V8

88V8 wrote:Yes, unless you don't mind your insulation disappearing.

Just a normal sand/cement mix. Let it go off before heating.

V8

Yep, I have some mortar patch mix which I've used to re-point a bit of brickwork. Suppose I could use that. Or is there not any sort of rubber collar which can go round the flue without the need to remove anything?

If it's only a few mm gap all round I'd have thought that a tube of decorators caulk and caulking gun would make for a neater job.

I just took a closer look and the gap is around 20mm in places. Suspect it might be tricky to fill.

I love the excuse to use expanding foam. https://www.screwfix.com/p/soudal-gap-f ... d_source=1

I'm thinking something like this might do the trick:

https://www.ventilationland.co.uk/en_GB ... LjEALw_wcB

kempiejon wrote:I love the excuse to use expanding foam. https://www.screwfix.com/p/soudal-gap-f ... d_source=1

Thanks, I've never used it. I take it the expansion is as it comes out from the can (not later)? Is it easy to wipe away the excess from a painted wall? If I let it set slightly proud, can it be sanded back later?

I would be worried about thermal expansion. I'd want something flexible. Amongst other things you can get unwanted noise if free movement cannot occur as the pipe expands longitudinally. Worse case a rigid grip could crack the pipe.

You can get "repair cement" that comes in tubes too.

https://www.screwfix.com/p/soudal-repai ... 90ml/705RG for example.

Scott.

swill453 wrote:You can get "repair cement" that comes in tubes too.

https://www.screwfix.com/p/soudal-repai ... 90ml/705RG for example.

Scott.

I have recent experience of using that exact product. You don't stand a chance of filling anything more than a few millimetres or so with it. It also doesn't adhere to the surface it's being applied to. It just falls off after application. The pressure required to extract the product from the tube with the typical trigger type applicator results in biceps like Arnold Swarzennegger. It's probably the poorest DIY product I've ever bought.

Seeing what's been described here, I should think by far the simplest and best fix is mixing some mortar and using a palette knife, fill in the gaps around the flue.

MrFoolish wrote:

kempiejon wrote:I love the excuse to use expanding foam. https://www.screwfix.com/p/soudal-gap-f ... d_source=1

Thanks, I've never used it. I take it the expansion is as it comes out from the can (not later)? Is it easy to wipe away the excess from a painted wall? If I let it set slightly proud, can it be sanded back later?

It's awful stuff to work with, has a mind of it's own. Depends of course where you are putting it. I've used it a few times.

To fill a hole in the wall, make sure you mask around the outer edges of the hole or it will come out and spread, difficult to remove from brick or plaster.

I've filled a void under a window cill by drilling holes at various points and putting foam in. It will expand along and come out of the holes. Left to set, sliced off over fill with a knife then fine surface filler and paint.

Third time was to sound-proof the underside of a toilet, (not the side you do your business in.) Toilet was off the wall so filled with foam and put a board across. Foam lifted the board so had to put bricks on the board. Powerful stuff.

So, will expand at will, once set can be trimmed with a knife and can be sanded. Wiping when wet just exacerbates the problem.

Regarding the painted wall, have a pot of PU foam remover handy https://www.toolstation.com/soudal-pu-f ... ver/p69416. Will only work on non-porous surfaces.

Just to re-iterate, use with care or you'll create more work trying to rectify the un-intended effects of the stuff.

Maroochydore wrote:It's awful stuff to work with, has a mind of it's own. Depends of course where you are putting it. I've used it a few times.

It is sticky and a bit of a skill to stop it over expanding or bonding in the wrong place. Like everything needs a bit of prep and using properly but I think is great for filling where there are big gaps, especially if there is a void behind the surface as the filler doesn't fall through. Like into around a pipe in a hole through from a cavity wall.
As said you can work it when set, trim with a saw, knife or sand. Working when wet is not advised, wear gloves.

Thanks for all the suggestions.

The expanding foam sounds a bit too scary as I'm naturally messy with such jobs. I've noticed it also has a lot of dire health warnings, but perhaps that's just 'ealth n safety gone mad.

It's not urgent so I'll continue to ponder....

The gas regulations require flue tubes to be sealed to both the inner and outer leaves of the cavity wall.

They don't care what with, as long as flue gases can't pass back into the house through the hole around the flue tube.

Silicone or decorators' filler will be fine on the inner face.

There are also foams that are not supposed to expand on sale at Screwfix etc, although I've only ever used the expanding variety.

After checking I don't need a fire-resistant variety, I would probably buy one of small cans of expanding foam from Home Bargains and trim off the excess after it's cured.

I've found some all purpose filler in a tube which remarkably hasn't set from the last time I used it. So I've made a start with this. It's a bit fiddly and tends to drop into the cavity. But I've now got a few "spokes" in place. When these spokes have dried, hopefully it will be fairly easy to fill in the gaps between them.