Pumped cavity wall: what do you use to fill a gap?

pleasant Co.

Hi, getting our gas boiler replaced next week and the new one has a higher vent position than the old one so a new hole will have to be bored. What should I use to fill the gap in the cavity left by the old boilers vent?

10-10-20

https://www.boards.ie/discussion/2058422811/pumped-cavity-wall-what-do-you-use-to-fill-a-gap

In a cavity wall or a breeze-block wall?

All things being perfect the cut-out from the new hole will suffice to partially back-fill the hole and then use a pre-mixed lightweight filler to patch the inside up after that.

If the cut-out isn't going to work then affix some light laths (thin pieces of timber) using instant grip adhesive to create a backing and then fill the hole with a stiff enough mix of mortar. Fit the laths on both the inner side of the outer wall and the outer side of the inner wall at the same time so that the cavity is maintained.

If it's a case where the job just needs to be done ASAP while the boiler is off the wall, expanding foam into the cavity will block it up. Once the foam has developed a skin on it (after about 7 mins) then you can push it back into the wall slightly to maintain a cavity to take a skim of mortar to close off the wall.

Hope it helps.

pleasant Co.

https://www.boards.ie/discussion/comment/123762442#Comment_123762442

Thanks for all that. Yes it’s a cavity wall that’s been pumped with insulating beads so was wondering what to use to fill the cavity hole to maintain the insulation. Had wondered if the newly cut core would suffice alright and had planned on using expanding foam / filler on the interior block as the new boiler would be covering it later in the day anyway if the cored bit of block didn’t work out.

Wearb

Is dropping the new boiler down so that flue aligns an option 🤔

pleasant Co.

https://www.boards.ie/discussion/comment/123762482#Comment_123762482

unfortunately not as that would require removing a countertop and sink.

Mr321

https://www.boards.ie/discussion/comment/123762442#Comment_123762442

I second the mortar mix approach.

I don't like the foam filler routes as vermon love it

standardg60

I'd worry about dislodging the insulation when removing the old vent pipe. Maybe easiest to just cut flush with the wall inside and outside and slap a couple of vent covers over the ends?

No harm having an extra room vent even if it's slightly covered by the new boiler.

pleasant Co.

https://www.boards.ie/discussion/comment/123762569#Comment_123762569

that’s true, and handily I have one spare interior vent cover here already so might just do that