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#66028 - 05/18/06 05:08 PM poke through  
Jps1006  Offline
Joined: Jan 2004
Posts: 615
Northern IL
Before I post my question, let me ask this. Has anyone else noticed that the search function on this site (for the general forum) will not generate a hit any newer that 12/31/04? I don't know for sure if that is the cut-off, but it seems close to it.

I am being asked to put a poke through receptacle in a stress-core floor. The one Graybar stocks is made by Hubble and needs a 3" hole. My question is do I need to core this hole with a bit (or hire out a bore) or can I use my Bosch rotary hammer and chip the hole out? How close do I have to be?

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#66029 - 05/18/06 06:24 PM Re: poke through  
earlydean  Offline
Joined: Dec 2003
Posts: 751
Griswold, CT, USA
Chip it out, then mud it in with some floor stone.


#66030 - 05/18/06 07:19 PM Re: poke through  
Gregtaylor  Offline
Joined: Mar 2005
Posts: 212
Boise, Idaho, USA
What do you mean by a stress core floor? A poured concrete floor with post tension cables? If so, you need to have the floor x-rayed to ID the locations of the cables. If you core drill through one you'll be sorry.

#66031 - 05/18/06 10:55 PM Re: poke through  
hbiss  Offline
Joined: Dec 2003
Posts: 886
Hawthorne, NY USA
How close do you have to be? Well, there is doughnut material that expands when heated against the sides of the hole. If the specs call for 3" then smaller or larger may compromise the seal in the event of a fire. You can't just bust out a hole and mud it in either. I always core drilled them.

Stress-core? Are these precast planks with hollow voids in them? Those cables you can cut but I would check with the manufacturer or an engineer first. Floors like Greg is talking about you don't want to mess with without supervision.


#66032 - 05/19/06 08:57 AM Re: poke through  
Jps1006  Offline
Joined: Jan 2004
Posts: 615
Northern IL
I'm calling it stress core because that's what the contractor referred to it as. I pictured prefab hollow core.

Good points Hal. Now, Hal, when you say you always core them, do you mean "you" core them, or have them cored? What would you do if you only had one?

#66033 - 05/19/06 11:38 AM Re: poke through  
LearJet9  Offline
Joined: Apr 2005
Posts: 197
Millis, MA USA
Jps - Unless you have a coring machine and have done it before, you better consider having a coring company do that for you. It ain't as easy as it sounds.

#66034 - 05/19/06 01:01 PM Re: poke through  
hbiss  Offline
Joined: Dec 2003
Posts: 886
Hawthorne, NY USA
Depends on where it is. In the middle of a carpeted floor no way would I touch it. During construction I would rent or borrow a core rig. Really isn't that big of a deal when you have the right equipment but it is messy. The one I've used floods the diamond core bit with water. You also have to set a couple of anchor bolts to hold the thing down unless you can use a jack post.


#66035 - 05/19/06 05:57 PM Re: poke through  
togol  Offline
Joined: Sep 2005
Posts: 421
there is also a core drill available that uses a vacuum to hold fast to the floor without drilling........he might also consider using a shop-vac to suck up the water while drilling


#66036 - 05/19/06 06:49 PM Re: poke through  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
The shop I work for owns a nice core drill set up. Yes we can use a vacuum pump to stick it down.

That said I feel much the same as Hal (hbiss) I use it when the surroundings are not 'to' finished.

If it's in the middle of a carpeted area we hire it out. If anything gets damaged it will be the core guys issue to deal with.

We dry core a lot of poke throughs into decks using a core bit for a large hammer drill. It works fairly well but you won't be doing it during a businesses operating hours. 10 to 30 minutes of very loud hammer drilling.

Finally if it is pre-stressed hollow core both the cables and the hollows present problems.

As has been mentioned you don't want to cut cables without an engineers blessing.

The hollows will prevent the poke through from maintain the fire rating.

Most need at least 4" of depth of the correct diameter.

Bob Badger
Construction & Maintenance Electrician

#66037 - 05/19/06 09:06 PM Re: poke through  
hbiss  Offline
Joined: Dec 2003
Posts: 886
Hawthorne, NY USA
The hollows will prevent the poke through from maintain the fire rating.

That's a good point. What are your alternatives if you need a poke-through? I have only had to deal with this once for one poke-through. I core drilled, covered the bottom from below with plywood and packed the voids a few inches back from the hole. I then filled the hole with concrete and when it cured I redrilled the hole in the exact same spot. Don't know if that was kosher and I'm glad I didn't have to do 100 of them.


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