Making good an oversize fan duct hole

[Diggory]

I’m fitting a 125mm diameter fan duct into a (cavity) brickwork hole that’s a fair bit larger.
It’s a bit of a sketchy hole so I guess it’s been chain-drilled and chiselled (many years ago).
It’s close to 150mm but not quite - I fear any further chiselling will break a brick or two.
So I want to leave it be and fit a 125 duct and make good the oversize hole.

Am I best to SBR the insides of hole, locate the duct and push in sand/cement with a pointing trowel.
Or would one of the hybrid polymer filler adhesives be better to fill the gaps with.
Or I even wondered about a tile adhesive with some brick red dye.

Appreciate any advice.

Best D

 

[CountryFan]

Perhaps some expanding foam wait until dry then just sand/cement finish?

 

[aveatry]

I had an uneven chiselled out hole and I wrapped the duct in paper then used spray foam inside the hole,i made sure that I didn't over fill so that it was about 1cm below the wall surface. Once set I could then pull out the duct and leave the paper lined tube hole there, then peal out he paper and that way the duct is not held by the foam so I could mess about with the lining up of the rest of the duct and it was easier to fill level with the wall with plaster without the duct being there.
Outside didn't not matter so much as the grill covered the oversize hole.

 

[noseall]

I’m fitting a 125mm diameter fan duct into a (cavity) brickwork hole that’s a fair bit larger.
It’s a bit of a sketchy hole so I guess it’s been chain-drilled and chiselled (many years ago).
It’s close to 150mm but not quite - I fear any further chiselling will break a brick or two.
So I want to leave it be and fit a 125 duct and make good the oversize hole.

Am I best to SBR the insides of hole, locate the duct and push in sand/cement with a pointing trowel.
Or would one of the hybrid polymer filler adhesives be better to fill the gaps with.
Or I even wondered about a tile adhesive with some brick red dye.

Appreciate any advice.

Best D

Where abouts is the hole located?

 

[Diggory]

Thanks @CountryFan - that did cross my mind.
(i was a bit wary about the cavity and how easy it is to over apply it)

@noseall - in gable end through to loft space.

Regards,

D

 

[Diggory]

Thanks @aveatry - I have some DPC on a roll; I could try wrapping with that.

Regards D

 

[noseall]

Thanks @CountryFan - that did cross my mind.
(i was a bit wary about the cavity and how easy it is to over apply it)

@noseall - in gable end through to loft space.

Regards,

D

We usually fit a short piece of pipe (duct) and foam it in.

 

[Diggory]

We usually fit a short piece of pipe (duct) and foam it in.

Sounds like foam might be the way to go then.
Does it matter if the foam bridges the cavity ?

Thx D

 

[noseall]

Sounds like foam might be the way to go then.
Does it matter if the foam bridges the cavity ?

Thx D

Use the low-ex plasterboard adhesive and use it sparingly.

 

[Diggory]

I think I have some of that - good idea.

Thanks D