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#67697 - 07/12/06 11:34 AM Electrical in Cast-in-place Concrete Walls?
SolarPowered Offline
Member

Registered: 07/05/04
Posts: 615
Loc: Palo Alto, CA, USA
I've been reading about concrete homes, which seem to be quite popular in Florida (hurricanes) and Kansas (tornados). I've been trying to figure out how they get the electrical into the walls. I've read that they nail some kind of boxes to the inside of the forms, and run conduit from the boxes, but how do they get the conduit out of the forms? They appear to normally use the Symmons-type reusable forms, so I'd think that drilling holes in the forms for conduit would be a no-no. (Especially for the $$$ aluminum forms.)

Also, what's the typical preference for metal vs. plastic boxes and pipe?


[This message has been edited by SolarPowered (edited 07-12-2006).]

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#67698 - 07/12/06 08:30 PM Re: Electrical in Cast-in-place Concrete Walls?
u2slow Offline
Member

Registered: 09/18/03
Posts: 198
Loc: Salt Spring, BC, Canada
I have done that kind of work on concrete high-rise condos. All forming was with wooden form panels.

Typically used 4x4" shallow boxes with an appropriate mudring. Then nail them on with a couple of modified 3-1/4" common nails. (nicked with diag. cutters so they snap off easily after the forms are stripped.) Utility and masonry boxes work also.

ENT (cor-line, smurf-tube, etc.) or rigid PVC for conduit. Usually stubbed up out of the wall - then tied into the next suspended slab/floor.

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#67699 - 07/13/06 12:13 AM Re: Electrical in Cast-in-place Concrete Walls?
e57 Offline
Member

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
Use a form liner, everything goes on that. They use all kinds of stuff, thin ply, even this wacky plastic card-board, and textured stuff.

Or - I have only done this a few times when the situation was right. Brace/wedge VERY VERY firmly against re-bar, tie wire it to death! Works great on cielings. Doing it this way on walls is risky, but you need to make very sure that the rebar is tied tight to the snap-ties and pushes solid against the form, or its a disaster. If you dont know or doubt it in the slightest, use 1/4-20 rod to jamb it against the other side of the form. (But only is the other side is not a finish surface.)

Or - I think they call them "Bucks"? They are plastic tabs that you can put between the seams and attach the boxes to those. But the seams need to be where the boxes go....

Or - Fir the wall out!

Building felt can be used to keep slurry out. Jamb some in the box, then make a gasket, and cut tight to box....

For conduit I'll use anything but Smurf, never again....
_________________________
Mark Heller
"Well - I oughta....." -Jackie Gleason

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#67700 - 07/13/06 09:33 AM Re: Electrical in Cast-in-place Concrete Walls?
SolarPowered Offline
Member

Registered: 07/05/04
Posts: 615
Loc: Palo Alto, CA, USA
u2slow, I'm trying to picture how you're nailing these things. I haven't seen any brackets on metal boxes that look like they'd be useful in this capacity, so I'm guessing you're nailing through the back of the box, though the opening in the mud ring, into the form. In which case I'd think that you're breaking off the nails close to the back of the box, but there's still a bit of nail left when you're done? Or do I need to "re-imagine" this?

e57, yah, I remember your comments about crushed Smurf, and how badly screwed one is when that happens. It seems to me that sched 40 is cheap insurance compared with recovering from blocked Smurf.

I found that Carlon has some stuff in their ENT line for this purpose--four square mud boxes that can be nailed to forms, and "stub downs" that can be used to transition tubing or conduit out of a form after the form has been stripped. I note that you can also use these items with sched 40 PVC, if one is staying away from Smurf in concrete.

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#67701 - 07/13/06 05:41 PM Re: Electrical in Cast-in-place Concrete Walls?
e57 Offline
Member

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
You are correct solar... That smurf blockage did not go down well after the LB got blasted in for surface conduit....

I'm not much of a glue sniffer anyway, but will opt for PVC and steel penetrations (Required localy), or all steel. IMO it its easier to work with, I'm not one for waiting for a hot box or blanket. Time is money.

Anyway, back to the OP, and the metal forms, the concrete crew was around chipping today. Yes they are reffered to as "Bucks", apparently you can get "universal" ones that get jammed in the seams, and you can screw boxes to them. But those can only go where the seam is.... So they are often not used. Apparenlty I'm not alone in the jamming it to the form method.
_________________________
Mark Heller
"Well - I oughta....." -Jackie Gleason

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#67702 - 07/14/06 02:52 AM Re: Electrical in Cast-in-place Concrete Walls?
Texas_Ranger Offline
Member

Registered: 12/17/01
Posts: 2343
Loc: Vienna, Austria
 Quote:
Building felt can be used to keep slurry out. Jamb some in the box, then make a gasket, and cut tight to box....

Newspaper works too... classic method of European sparkies to keep the plasterers from filling their boxes. (Usually the boxes are fastened to the rough brick walls using a glob of gypsum plaster and then the plasterers come in and finish the surface...)

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