Best way to drill a 4" hole?

[RigidRaider]

We are installing a loo vent. I will hire a 4" core drill and will line the hole with some soil pipe so as to bridge the air gap. The outside wall is reconstitued stone blocks and the inner is breeze bocks. Recently I cut a similar vent hole with the same drill, going from outside the house inwards and it worked fine.

I plan to drill slightly downhill going outwards so that any rain running down the wall won't run inside.

Any other hints or tips for using these rather large and powerful drills? This time I shall be working at the top of the wall and since the ground outside is a good 18" below floor level I'll prefer to work from inside. This also makes the measuring a lot easier!

 

[JohnD]

It will be quite dusty. If you can choose a day when the wind blows into the house from the other side, and blows out through the bathroom window, that will be ideal.

Make sure you are standing on something very firm, as you will presumably be holding the thing at shoulder height, and moving forward by a step as the drill penetrates. You do not want to fall forward when it breaks through.

You can poke your arm through the pipe and winkle mortar into the gap on the outside wall with your fingers, if it is not an easy height to get to. If you have cavity insulation, roll a bit of loft mat into a tube to line the hole and fit round the soil pipe (cavity insulation can be quite loose and fall down when you make holes in the wall.

Get a sloping cowl with a backdraft flap.

The ones like venetian blinds rattle annoyingly in the wind.

They are available from builders merchants or the tumble-drier parts section of your DIY shed.

Mine are all brown to tone with the house but you can get grey, or can paint them with non-drip gloss (no undercoat) before fitting. Fix with brass or stainless screws. If it ever breaks you will want to be able to take it off easily when perched up a ladder in the rain.

 

[RigidRaider]

Thanks! Good idea on the cowl. Will have a look in SoditAll at lunch time.

 

[RF Lighting]

Just make sure you hold the drill very firmly, and never get complacent with the drill, no matter how well it is going.

If a diamond core drill snags it will not give you any warning, and break your wrist without even trying.