Core drilling a solid wall

[andrewpreece]

My brother has asked me how I would go about coring out a hole for a boiler flue in a solid wall ( 1900 terraced house, wall over a foot thick at that point, construction seemingly stone/rubble/stone ).

I confessed I wasn't sure that if he hired a core drill it would be long enough, nor whether it would have problems with the rubble fillng the centre of the wall.

So, does anyone have any experience of this type of problem, or perhaps it's not a problem, however the centre of his house walls are quite crumbly,

cheers,

Andy

[Grunff]

Sounds a lot like our walls, but quite a bit thiner. A core will work fine, you'll just need to chisel out the core 3-4 times before you get through.

[andrewpreece]

Thanks, I'll pass it on.

Andy

[andrewpreece]

Thanks for that,

My brothers has decided that since he has plenty of money, but no time, he will get someone in to do it. I've a feeling that what'll happen now is that noone will be interested/contactable/turn up! Still, I'll pass on your advice in case he needs to do himself, As it happens I have a 25mm drill that'll reach >16" so that'd be OK for a pilot hole.

cheers,

Andy.

[Jim Warren]

Sounds like my house, except I have brick inner, rubble infill, stone outer.

You can use a core drill, but be careful that the hammer action doesn't try to push out the outside stone rather than cutting it. Try putting a small pilot hole right through, and then using the core drill from the inside through to the end of the rubble infill, and then from the outside to meet up.

Mind you, in my case, my later (replacement) boiler had a rectangular balanced flue. That was a job and a half, making a suitable rectangular hole through a 14 inch thick wall!

Jim

[andrewpreece]

rectangular

Good point, I have a 12mm of the same length so if he does try it I'll recommend using that one,

Andy.

[Ian White]

Could be that a 25mm drill without a pilot hole - or rather, the 4kg SDS+ machine that's big enough to drive it - would risk dislodging whole big stones and just shaking out the smaller rubble and mortar from inside the wall. A smaller pilot drill might do better.

If I can go beyond Andy's original question...

There are some jobs coming up soon that involve drilling large holes through 600-750mm walls made of granite rubble. It's going to be too deep for drilling a pattern of smaller holes and then breaking out, so I'd have to use a core drill eventually. Any advice, please?

Even a small pilot hole looks problematic in this depth. The next readily available length of SDS drill beyond 450mm seems to be 1000mm. Any unnecessary length will obviously decrease the efficiency of the hammer action and increase the risk of a thin drill snapping. Again, any advice, please?

[Dave Liquorice]

I've got some 1000mm drills but have yet to use them. I suspect that to start off the hole they will be so uncontrolable as to be useless. If I ever do use them I plan to start with short small drill and work up both in diameter and length. Only switching to the 1000mm jobbie when the next longest drill of the same size has reached it's maximum depth. The idea being that the 12" or more of existing hole guides the much longer drill. I still suspect keeping the thing true will be "fun".

[Jim Warren]

There used to be a type of drill bit that had a threaded part at the chuck end, before stepping down in diameter to the part that went into the chuck. Then you could get extension tubes with an internal thread one end and the same thread/stepped down end at the other.

You used the drill alone until the start of the thread was flush with the wall, then added an extension and carried on drilling, then added another extension, until eventually it came through the other side.

I got my set some years ago. They were not SDS but my heavy duty drill with a 1/2 inch chuck drove it OK. Sizes 5/8, 3/4, 7/8 and 1" in the set. Don't know if they are still available though.

Jim