# advice needed for coring concrete overhead



## rshackleford (Jul 2, 2007)

I need to drill 200 holes each of 4.5" and 2". They are all overhead through a two inch concrete ceiling.

Architect will not allow a hammer drill.

Suggestions?


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## 480sparky (Feb 1, 2009)

Sub it out to a coring contractor.


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## The Coastal Craftsman (Jun 29, 2009)

Core bits should never be used on hammer so yes they need to be core drilled if they say no hammer drill. Are you allowed to hammer drill a pilot hole for each core hole so you can drill the holes from above. You can buy and rent core drill bits that have a centering shaft that goes into the pilot hole to keep your core bit on center. That's what we used to do when they required hole to be made with no hammer drills. You still get the nice clean hole from the core bit and you have the ease of drilling from above. Is it the noise they are worried about or the messy hole finish?


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## rshackleford (Jul 2, 2007)

It is a hollow floor and we are not drilling all the way through. It seems impossible to mount a core drill on the ceiling.

We could hammer drill a pilot.

New construction. Noise is not an issue.


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## rshackleford (Jul 2, 2007)

Coring contractors don't exist where we are.


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## The Coastal Craftsman (Jun 29, 2009)

I have seen the core drills that mount on a Jack kind of system and you pump them as you core drill. The post holds the drill and the drill goes up and down on the post. It was a specialist bit of kit though and not something you would get from a rental store. What's the reason for needing all these holes if they don't pass through to another floor? Interested to know what they are used for.


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## griz (Nov 26, 2009)

Is there a concrete cutting guy around?
They usually have all the drilling/boring equipment also.


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## 480sparky (Feb 1, 2009)

griz said:


> Is there a concrete cutting guy around?
> They usually have all the drilling/boring equipment also.



X2. Usually, they do both, and most advertise as cutters.


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## rshackleford (Jul 2, 2007)

No concrete cutter contractors in our area. Probably one three hundred miles away.

The holes will house a light fixture box and the hollow concrete floor/ceiling will be used as a raceway.


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## mudpad (Dec 26, 2008)

Whats your location? if there is concrete construction around it's hard to believe there is nobody that cuts and cores it. For a couple hundred holes most of the ones I know would drive a ways.

Are you talking about precast planks?


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## one man show (Dec 20, 2010)

*Coreing*

Eat your wheaties


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## woodchuck2 (Feb 27, 2008)

one man show said:


> Eat your wheaties


X2, and wear your rain gear cuz your going to get wet!


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## Wirenut103 (Dec 30, 2010)

480sparky said:


> Sub it out to a coring contractor.


If you are not familiar with core drilling, it is most economical for you to sub it out as 480sparky stated. For that many holes, I'm sure you could get someone out there....in these times, people are traveling far for work.


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## Inner10 (Mar 12, 2009)

How about these guys? 

http://www.overheaddrilling.com/index.htm


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## rshackleford (Jul 2, 2007)

We r on the montana, north dakota, canada border.


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## rshackleford (Jul 2, 2007)

we have a plan.

we are going to buy a Milwaukee 4079 Motor and 4136 vacuum base. For this we will also get the 2" and 4.5" bits.

we will mount the motor upside down so that we drill up instead of down with the base in a normal position. 

from here we have two options we have not decided on yet. we are either going to mount the drill base to a lift and drill up to the the ceiling or build an extended post so that the drill can vacuum mount to the floor and still reach the ceiling. 

we will use water but as little as possible and use a shop vac to suck up the water.

any thoughts?


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## griz (Nov 26, 2009)

Your sorta on the right track. Gravity is going to keep the water away from your coring spot. It's going to take more water than you think. Also the water is going to run down on to the drill motor. Is it waterproof being upside down?


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## rshackleford (Jul 2, 2007)

the water will be a trial by error situation. i think we will also have to use a tarp and some duct tape to create a shield around the motor.


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## flashheatingand (May 3, 2008)

Why not drill down?


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## mikeswoods (Oct 11, 2008)

He said that they were only drilling half way through--into the hollow center---


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## 480sparky (Feb 1, 2009)

OK, so what's the plan for running power from the hollow slab cell into the wall? :blink:


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## rshackleford (Jul 2, 2007)

With precast concrete the addatives make the concrete brittle. We tried a hammer drill on a damaged plank and it shattered like glass.


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## concretemasonry (Dec 1, 2006)

rshackleford -

You better do a little research on the core arrangement to make sure you can hit the open cores. All hollow core planks have parallel longitudinal cores, but there is a big difference between manufacturers and equipment used. - Some have nice round cores like you drew, others have more much smaller cores that can be tough to hit. You may even find some with cores that are forms with lightweight aggregate to maintain a very rough and crude sort of rectangular core, but much of the aggregate is left inside and could affect the installation.

Common plank widths are 16" (rare), 24", 40" (one meter), 48" and 96", but there also a few exceptions. The construction manger, designer or G.C. must be aware that the location of the cores you drill must be "fine tuned" to hit the cores of the plank that was ordered and delivered. There is no such thing as adjusting the core size or location because that affects the entire engineering of the plant and is very costly, if even possible.

Since it is under construction, find out the name of the supplier to get information on the core arrangement, spacing and size. This would include the core size, spacing web thicknesses and the reinforcement type and location. Don't count on it being the closest supplier, since plank can easily be shipped up to 1000 miles depending on the jon and spans. The concrete used ends up being very high strength (6,000 to 10,000 psi) by the time it is the building since it usually about 4000 psi when the plank is removed from the forms the next morning. - Not like job site placed and cured concrete that can really be a guess.


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## mudpad (Dec 26, 2008)

I agree with Griz, a sub is the way to go. I have never regretted subbing out this kind of a specialty thing, but never worked out in the tundra like you appear to be either. 

Also agree you have to know where you are coring, so that you can hit the hollow cores in the planks. In between is reinforcing, and if you cut that you have problems. The planks that I have had experience with will let you cut one tendon, as many times as you want, but no more. You have to consider that some other trade will need to cut as well, such as water closets, which have no "wiggle" room to stay in code. 

It appears from your sketches that you have figured this out and have access to the plank shop drawings. Light fixtures can usually be fudged one way or another to stay in the hollow core.


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## 480sparky (Feb 1, 2009)

mudpad said:


> .......... In between is reinforcing, and if you cut that you have problems............


_Very, very expensive_ problems!


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## Remodelor (Nov 5, 2010)

Why is this post in the electrical forum?


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## 480sparky (Feb 1, 2009)

Remodelor said:


> Why is this post in the electrical forum?



OP wants to install light fixtures.

That, and the world revolves around electricians. :thumbsup::laughing:


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## flashheatingand (May 3, 2008)

It sounds like you have a plan. 

Just being a couch contractor, as it's easy when you are just looking at the screen. This is just a thought, and It's likely full of holes.... It looks as if it would be ideal to drill the ceiling and call it a wonderful thing. What if you were to cut a square (12"x12") with a circular saw, box in and patch. Quicker and cleaner with the cutting....?


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## mudpad (Dec 26, 2008)

480sparky said:


> OP wants to install light fixtures.
> 
> That, and the world revolves around electricians. :thumbsup::laughing:


At times one would think so. But the GC is holding all the $:thumbup:


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## rshackleford (Jul 2, 2007)

> You better do a little research on the core arrangement to make sure you can hit the open cores.


we can see many of the ends of the planks so we have some very good reference there. also from the bottom side there are light and dark spots which correspond with the hollow cells. i have never dealt with these planks in the past as my part of the company is underground construction, so i have learned a lot this last couple days. fortunately, the gc and our guys on site are aware of these tension cables and it is well within our radar. thank you for helping keep it there!


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## rshackleford (Jul 2, 2007)

See planks.


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## 480sparky (Feb 1, 2009)

mudpad said:


> .......... But the GC is holding all the $:thumbup:


And truth be told, his shît still stinks.


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## mudpad (Dec 26, 2008)

480sparky said:


> And truth be told, his shît still stinks.


:thumbup::thumbup: Where'd you find that smilie?


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## 480sparky (Feb 1, 2009)

mudpad said:


> :thumbup::thumbup: Where'd you find that smilie?


I have a ton of 'em on my Photobucket account.














































​


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## rshackleford (Jul 2, 2007)

it is going decent. we have gotten about 25 done in four hours. that's about ten per minute. we are using the new milwaukee drill rig that we picked up yesterday. 

we had some issues with the freezing temps and our weather so we are drilling with straight window washer fluid.


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## 480sparky (Feb 1, 2009)

rshackleford said:


> .... we have gotten about 25 done in four hours. that's about ten per minute.......... .


:blink:






You mean ten minutes per.......


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## rshackleford (Jul 2, 2007)

sorry. about one per ten minutes.


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## 480sparky (Feb 1, 2009)

rshackleford said:


> sorry. about one per ten minutes.



At ten per minute, you should start your own coring business! :laughing:


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## Tinstaafl (Jan 6, 2008)

480sparky said:


> At ten per minute, you should start your own coring business! :laughing:


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## rshackleford (Jul 2, 2007)

that doesn't include the layout. the actual electricians are marking the spots to core. i have a couple of equipment operators doing the coring.


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