Increasing the size of a hole for ducting through cavity walls

dreamypuma

Having fitted a new kitchen extractor, the ducting we need to fit requires a larger hole through our cavity wall.

The current hole through the cavity wall is between 110mm and 120mm diameter. The new duct requires a hole of 150mm.

I was looking at using an 150mm core drill bit to go through the outer leaf from the exterior and inner leaf from the interior to create a little damage to the walls as possible. As a smaller hole exists already in the same location, I'm assuming that this is not going to be as easy as drilling a new hole. Is there an easier way of doing this?

Dognobs

core drill will fit but can you nor reduce it from 150?

dreamypuma

Dognobs wrote: »

core drill will fit but can you nor reduce it from 150?

We cant reduce the size of the duct, as we tried this. We originally fitted a 100mm flexible ducting, but this damaged the extractor (the impeller I think) and it was repaired as goodwill under the warranty.

DVardysShadow

Your problem with a core drill will be keeping it centred while getting a start on your hole. Now, I have never had to do this, so you will need to fill in the details yourself. What I would try would be wedging wood firmly in the existing holes and drilling a clearance hole in the wood which would allow the core drill pilot to centre while you start your new core cuts.

karl-123

buy a reducer widely available,

or get a lump hammer and sharp long chisel " be carefull " wear goggles,

karl-123

trying to increase an existing core hole to make it bigger with "any" core bit,

attatched to your drill is ( dangerous ) get yourself a long sharp chisel ,with lump hammer and goggles,

or a 4 " to 3 " reducer for your existing vent,

ormus

1. try and use the 150mm drill very carefully to start with. use pencil marks to mark it out. you may get away with it.
2. fill the hole with mortar and then re drill the hole. slow as itll take a good few days for the mortar to harden.
3. hammer and chisel, then make good afterwards.
4. make a jig out of say 2x2. with a 150mm hole. fix to the wall or have a strongman to hold it up. for starting the hole.

(pretty safe if the drill has a clutch).

like so,

tony6403

The simplest way is to mark your new hole size onto the wall with a large felt tipped pen - inside and outside - and , using a 8 or 10mm masonry drill bit in a hammer drill, stitch drill around these circular markings. By this I mean drill as many 8 or10mm holes as you can around the desired hole size. Make sure that you drill at 90 degrees .Then use a lump hammer and small chisel to break away the excess material between the numerous 8/10mm stitches.

27col

That's a pretty good idea ormus. I must confess that I would not have thought of that one. I would have probably chain-drilled it, and then finished off with a chisel and bolster.

dreamypuma

Thanks for all the advise. It's really appreciated Think I may try filling the hole with mortar first, as this almost takes me back to day one, then I can start again.

dreamypuma

karl-123 wrote: »

trying to increase an existing core hole to make it bigger with "any" core bit,

attatched to your drill is ( dangerous ) get yourself a long sharp chisel ,with lump hammer and goggles,

or a 4 " to 3 " reducer for your existing vent,

Thanks a but a reducer is not an option due to the power of the extractor 150mm is the minimum I can vent out by.