drilling through concrete walls: how to?

[Stephen]

Hello,

I tried to drill a hole through a 500mm concrete wall yesterday. I was hoping to put a 15mm copper pipe through to an outdoor tap (you may remember my other thread about the old pipe freezing and bursting).

I was unsuccessful. I used an sds drill and I got through the wall quick enough but although I (thought I) held the drill level, the exit hole and the entry hole were at two different heights and passing a pipe through was impossible.

Now that I know from the "one metre drill bits at Aldi" thread that these bits are flexible, is it possible that the bit deflected inside the wall?

How can I prevent this in the future? I drilled from one side straight through. Should I have carefully marked each side and drilled from each side, hopefully meeting halfway?

For drilling though brick I have used a 16mm bit for 15mm pipe in the past. Do I need to use something bigger than 16mm in concrete to allow for it not being straight?

I was using a 6kg Titan drill I got from Screwfix some time ago. Despite being a budget model it has served me well. I had a Bosch drill bit in it. I had not used the drill bit before and I won't be using it again as the end broke. I had expected better longevity from a branded bit. Are the clutches on sds drills like those on cars, i.e. do they wear out eventually? I ask because mine worked once or twice yesterday ;(

Thanks, Stephen.

[A.Lee]

Yes. I used to drill deep through-holes in steel. It was rare for the drill to stay square to the bed for more than 8 inches.It could be half an inch out on a foot long hole. That is in steel, which is a pretty consisitent structure thoughout. Concrete has all sorts of holes and stones in it to deflect drills, so it would be unlikely to get a true, straight, level hole through such a length.

Yes. 20mm would be suitable for 15mm pipe, maybe even 22mm. Alan.

[Chris J Dixon]

If you try to pass the drill back through the hole, does it still go? Can you pass a stiff but flexible wire through the hole?

It is possible that a fragment of the concrete that was disturbed during the drilling has now dropped and is obstructing the hole.

Chris

[slider]

Use plastic pipe rather than copper

[Dave Plowman (News)]

Don't think they're *that* flexible. Did you try drilling through again from the other side? And moving the drill in slowly? Concrete has 'stones' in it which can deflect the cutting part of the drill enough to cause a less than perfect hole.

I'd tend to use a drill quite a bit larger than the pipe and sleeve it with PVC where it passes through the wall - you can get clip on sleeves designed to pretty up radiator tails which work fine.

[TheOldFellow]

Me too. I use WC solvent-weld overflow pipe (22mm OD/19mm ID). I've also used it to put radiator tails in a stud wall - as a conduit. Useful stuff, and dead cheap.

R.

[<me9]

I would make it 25mm, and line it with 22mm plastic pipe, reduces corrosion.

[Dave Liquorice]

Sounds like you were over loading the drilling system. You don't need to lean on a SDS drill like you do an conventional hammer drill. The SDS action does the "leaning" for you. All you need to do is keep the drill bit reasonably, but not hard, against the bottom of the hole and let the SDS action do the cutting work. Enough pressure so that the bit isn't bouncing about on the bottom of the hole.

Leaning on the drill, particulary with a long bit, is going to make it flex/bend and deflect off harder bits in the wall rather than drill through them.

It's probably asking a bit much to get a 15mm pipe through a 16mm hole as well. As others have pointed out it really ought to be sleeved. Cement and copper don't get on...

[Harry Bloomfield]

Stephen used his keyboard to write :

The hole diameter needed to be larger, as others have said to allow the pipe to be sleeved and to give the clearance to be able to get your pipe through. Something like a round bit of wood with an out facing pointy end, put in the pipe end - would help to align the pipe to the second part of the hole.

[John Rumm]

To an extent you may have been unlucky, or perhaps your technique was partly at fault. However to illustrate just how much flexibility there is in a drill bit:

?title=Image:Drillflex2.jpgThe first photo is the end of a 1m 16mm diameter SDS bit - the other end is hooked under the edge of a bench vice. A 14lb weight on the end will deflect it a good 3 - 4"

Not much chance of that!

Drilling through first with a 8 or 10mm bit can help - then enlarge it to the final size after.

Letting the drill do the work is the key - not applying too much force. If the clutch on the drill activated then that is a good indication that something is not going right.

For deep holes, you will need a wider bit.

As others have suggested, something that can take a plastic sleeve pipe is even better.

Sounds like the end got snagged on a stone or something - or perhaps it lost its carbide edge on one side and hence started drilling unevenly. The clutch can slip multiple times without any ill effects usually.

[Dave Plowman (News)]

Possible - but then the pipe would bend as easily.

[Stephen]

You can pass the drill through the hole, in fact you can see through the hole, so the hole is clear, it's just that it slopes an inch/two inches downward!

[Stephen]

That would have worked but I was trying to use this wall plate that had an integral copper tube:

you had used a plastic pipe, how would you have secured the tap to the wall?

That said, I don't know how good the wall plate above would have been. I think the three screw holes would have been too close to the hole I had made for the pipe and I may not have been able to secure it.

[Stephen]

Yes, and it came out somewhere else on the other side. I had a wall that looked like cheese, it was a complete disaster!

I was going to use overflow pipe to sleeve it but never got that far.

[Stephen]

Perhaps that was my mistake then. I don't remember consciously leaning on the drill but I guess I must have done without realising it. Perhaps it is an old habit from the old days of pre-sds drills? I haven't had any trouble before but then again, I haven't done a deep sds hole before now.

I think I have used 16mm holes in wood and brick to pass pipes through but for concrete it clearly doesn't work.

I know cement and copper have been discussed on the group before but I didn't think there was any consensus whether they corroded or not. I seem to remember people arguing both sides. I was thinking of lining it more for protection so the copper did not get scratched on the jagged edges of the concrete.

Our house was built with copper CH pipes buried in the concrete floor. I thought this was wasteful as it was heating the concrete, not the radiators. The 30 year old copper pipe was black. Is that a sign of corrosion? But it certainly was not leaking and it was 30 years old.

[Dave Liquorice]

15mm tube is far more ridged than a 16mm drill. The drill is also far more likely to drill a hole with a kink in it(*) rather than a smooth and even bend. A hole with a kink requires the bend in the tube to move along the tube as you (try to) put it through the hole.

You'll get away with a small deflection but not much more than a few mm in every 300 or so.

[John Rumm]

So if the hole is straight, a pipe would also go through it... The only problem you then have is if you want to have a pipe lead straight up or down to it, and you would hence need a 87 degree elbow or similar.

[John Rumm]

Sounds like you need the more traditional:

way the pipe can come out the wall at any angle, and the turn into the *side* of the fitting with the aid of an elbow.

[Stephen]

That's exactly what happened. A brand new, never used, drill bit went into the wall, and when it came out the carbide edge was only present on one side. It was a Bosch bit too, so I had expected better.

I remember trying to drill small holes in a concrete floor so that I could screw carpet grips into yellow plugs. I used Bosch bit for that and it melted! Perhaps I was too heavy handed that time too? But my experience with this limited number of Bosch bits has not been positive; perhaps they are just rebadged? I've used the cheapest Toolstation bits without problems. YMMV etc.

[Stephen]

Yes, I was able to pass the pipe through but the fitting was not flush with the wall; it was at an angle.