Core drilling for 150mm cooker hood ducting

Discussion in 'Builders' Talk' started by teucht, Jun 21, 2021.

  1. teucht

    teucht New Member

    I'm going to run the ducting for my cooker hood through the kitchen wall.

    It is 150mm, so I need to core drill a suitable size hole in the cavity brick wall. I always try to use rigid ducting if possible, so I was planning on using this

    However, it seems unlikely that a 152mm core drill bit will be big enough for this ducting, surely the wall thickness is more than 1mm?

    The other thing is my local hire shop has no diamond core drills in just now, so I was thinking of going for it with my trusty Makita DHR242. It hasn't let me down before with smaller cores, lots of drilling and breaking, but I wonder if this might be a bit much for it? It does at least have a torque limiter so shouldn't throw me off the ladder...

    Any advice welcome, as always!
  2. Peterdevon

    Peterdevon Active Member

    stitch drill it, you new a proper core drill to turn 150mm
    teucht likes this.
  3. FlyByNight

    FlyByNight Well-Known Member

    Does the drill have a clutch - if it does, you should be OK, if it does not, then do not use it.

    Have you considered using a circular to rectangular adapter? That way it is easy to cut out bricks.

    If you do decdie to dril and decide you can do it safely, then work from the INSIDE. Drill a full depth pilot hole to break out, then, go to te outside and using the core, make a 5-10 mm deep cut that is all and stops the core causing the brick face to break away. Back inside and drill the full hole all te way through, taking your time and clearing dust regularly.
    teucht and Tilt like this.
  4. Tilt

    Tilt Active Member

    ^^^ Agreed.
    @teucht I've drilled quite a few 6" cores with my Bosch GSB 2-26DRE and a lot of 40mm too and it has been fine. Still going strong.
    Agree with Flyby on his other comments too but cores are difficult to keep straight to match it up to the outside.
    Usually manage to meet them up somewhere in the wall though, Lol.
    teucht likes this.
  5. FlyByNight

    FlyByNight Well-Known Member

    I use a GBH 2-26 DFR now around 14 years old and have often done 100mm + cores. Time and patience is what is needed.

    Yes, you can get alignment issues going through but with a full pilot the offset can be very small. The reason I always do a small cut from the outside is to stop the break out (spelching) that can occur. It is easier to go to te middle from both sides, but as soon as a ladder in involved - inside to out is much safer.

    The OP mentions 152mm and will it be big enough. With "wobble" it might, but I would prefer a 162 core. For 4" - it might squeeze through a 107mm but I wil go for a 117 to make sure.
    teucht likes this.
  6. teucht

    teucht New Member

    Cheers for the input, always good responses on here.

    Drill does have a clutch, so I should be safe enough.

    I'll probably have to do it from outside as the duct will be in the kitchen ceiling, but if I can I'll do it from inside (under the floorboards...). As @FlyByNight I'll be on a ladder otherwise which is not ideal.

    Aye, 162 much be the answer. I've seen folk saying that ID 150mm stuff is more like OD 156, so 162 is probably a better bet.
  7. Tilt

    Tilt Active Member

    Purchasing the item first and measuring it is probably an even better bet..;)
  8. teucht

    teucht New Member

    Haha aye I'm off to pick up a wee bit of the ducting today to see how it will measure up.

    I think I've gone off the idea of putting it in the ceiling too. The space between the floorboards and the ceiling, and the exterior wall, and another wall, and the joists, and the gutter is very tight and I'm worried about getting the core drilled bang on through a pretty loose and rubbly inner skin of brick. I think I'll just run it in the kitchen (run is <2m) and either box it in nicely and hang horse brasses of the box or something or have a trendy exposed duct.
    Last edited: Jun 23, 2021
  9. teucht

    teucht New Member

    If anybody is interested in an update:
    • borrowed a 110v/850W core drill off a mate, and a 152mm (I.D) diamond core bit
    • checked the O.D of the core would allow the ducting through
    • took up the floorboards, drilled a pilot hole from the inside at the correct height
    • went up a ladder outside, rammed the pilot bit for the core through and just battered away with the core until it was through.
    • Very hard render and bricks meant it took a good 1/2 hr to go through the exterior wall, got up to full speed on the drill gradually and had breaks every 5-10 mins as the whole shebang is pretty heavy to use up a ladder
    • Was a wee bit dodgy up the ladder but didn't feel dangerous. Makes a hell of a mess though with the dust.
    • Much quicker through the interior course of red brick
    • Used 6'' rigid ducting, up through the kitchen ceiling and out through the wall
    • Had to mastic around the outer louvre as it is a weather battered wall and the exterior harling is very quite large
    All good but I wouldn't attempt it without a proper core drill, and next time I'd try and get a sharper bit. Thanks for all the advice as always!

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