Advice on core drill and bits for reinforced concrete floor

[Rickety]

Hi,

I am working on fitting out a new floor extension on a typical Swiss 'bunker style' from 1970s with reinforced concrete slabs. I need to drill some holes to take 110mm soil pipes, and heating loops etc through two existing concrete floors. These floors are 200-250mm thick, and have a mix of 10 & 14mm roobar in them.

Attached is picture of an exposed part of construction. Please note this shows slab at a critical point near structural wall. Where I'll be drilling doesn't have same density of bars. I've checked with architect that it's ok to make holes where I plan.

Slab construction

• Rickety
• 7 May 2013
• 1

Previously I made a 150mm hole using a circle of 12mm bit, but it took a very long time. I was quoted CHF 3400, nearly 2000 pounds to drill these 8-10 holes by a Swiss masonry company who did lots of the work on extension. And before you ask they are relatively cheap and good compared to others here - it's just that small jobs are very expensive....

I could fly someone out on holiday for that price, but instead I'm looking at buying a proper core drill, doing myself and selling after (hiring is not option here as very few people do DIY).

Looking on the Bosch site, it looks like these combination would be suitable for job:

Bosch GBH 7-46: http://www.bosch-professional.com/gb/en/gbh-7-46-de-8848-ocs-p/
Will do cores up to 150mm diam, about 500 pounds on ebay.

Bosch diamond bit: http://www.ebay.co.uk/itm/BOSCH-F00...Home_Garden_PowerTools_SM&hash=item3367d61713
Too big but I can probably source another one of right size.

Much cheaper ELU TCT bit: http://www.ebay.co.uk/itm/ELU-E3351...Home_Garden_PowerTools_SM&hash=item4aa814b2e5

Anyone have some thoughts on this - as I will be back in UK soon I want to make sure I get right kit rather than have to buy at inflate prices here.

I assume a proper diamond core bit is required, and the TCT one will just wear out?
Are there better makes/models than this Bosch one?

Whatever I get will probably wind up on eBay once all the work is done, so the resale value is also a factor.

Thanks very much

Rick

 

[RF Lighting]

Forget all about TCT cutters. For a start they only drill to about 60mm deep, and they will be ruined the first time you touch a piece of rebar. Both the drill bits you linked to are TCT drills.

The seller even says "provide clean round holes in blocks, bricks and light concrete" Your building looks the complete opposite of light concrete!


You need a proper diamond corer for this sort of work.

You will need a drill like this:
http://www.ebay.co.uk/itm/Hilti-DD1...owerTools_CA&hash=item20d265f406#ht_256wt_958


A vacuum pump to attach the drill to the floor:
http://www.ebay.co.uk/itm/Hilti-cor...PowerTools_SM&hash=item2c6e90d563#ht_89wt_958

And a blade:
http://www.ebay.co.uk/itm/HILTI-DD-...owerTools_SM&hash=item27d1d41b97#ht_108wt_958


It's a lot of money to buy, but the drill and vacuum will hold their value well, and should resell for similar money.

 

[Rickety]

Thanks for this, that is useful info. Increasinlgy seems like only three options:

i) Lash out on a proper 2nd hand wet diamond rig, and try to recover money when reselling
ii) Grit my teeth and pay the money for someone to do it.
iii) Go back to the tested but slow process I used before - make a ring of drill holes, and break out with a big chisel bit.

It doesn't seem to be worth trying to find a dry core drill setup as none of them are really up to the job?

I'd look into hiring again, but I really doubt anyone hires out something as professional as option i).

Richard

 

[catlad]

I don't know what drill you were using to stitch drill, but a good quality heavy duty will speed things up, and if you start with say 12mm and bore them out to 25mm you should end up with a decent hole.

 

[Rickety]

I was using a very cheap (£40) 'Matrix' drill with a 12mm bit.
http://www.swissm.ch/en/html/swissmLine/hammerdrills2.htm

For the money it's actually ok, but for a job like this a clutch (which this doesn't have) seems vital. I recall nearly breaking my wrist when doing it.

This Bosch drill, which goes for about £500 looks good to me: http://www.bosch-professional.com/gb/en/gbh-7-46-de-8848-ocs-p/

Or would anyone recommend another one? I looked at Makita but for the same money the spec (Joules impact, drilling capacities) seemed lower.

I'll probably buy a TCT core bit and see how that works too. I assume you use these with hammer action? The Bosch drill above only has chisel or rotary hammer modes - no pure rotation.

Cheers

Rick

 

[catlad]

That drills spec says its has a 150mm core capacity, but if that does not work you could make a template out of some plywood by marking round the pipe you need to use, leaving a bit of room to play with get a two pence piece and draw round the circle you have made with the pipe overlapping slightly until you get all the way round, in the middle of each of the small circles you could drill 6mm holes and that way you use that to set out each time.

 

[Norcon]

An 18 joule breaker will punch its way through that with ease.
When you reach the rebar you change the chisel to one with a sharp edge and it will just shear the re bar off like a knife through butter.
Hilti chisels are the best.

 

[Jackrae]

Or if you want real "fun" with minimal "effort" you could burn the hole using a thermal lance.

 

[Brigadier]

There is no cottage - he's a trainee bank robber, and he's going for the vault