Need to traverse marble floor by cutting 10 feet trench

[wyreman]

Hey guys!
There is no basement
Can't use overfloor raceway
Can't drop from above
It is a display case in hi end store
Marble on concrete
Right in the middle of tile floor, an island

How deep to cut a groove for uf cable
Code would want 4" and/or gfi it. Also
Don't want to have cracks later
How to temp plug the groove after the first night ?
Wedge in a length of wood?
Need obviously the skinniest cable that will carry 3#12s
Thanks guys!

 

[growler]

Hey guys!
There is no basement
Can't use overfloor raceway
Can't drop from above
It is a display case in hi end store
Marble on concrete
Right in the middle of tile floor, an island

How deep to cut a groove for uf cable
Code would want 4" and/or gfi it. Also
Don't want to have cracks later
How to temp plug the groove after the first night ?
Wedge in a length of wood?
Need obviously the skinniest cable that will carry 3#12s
Thanks guys!

Interesting problem. I think I would contact a hole cutting outfit and see if they have any equipment for boring under the floor.

High end store, marble floor, I don't like the idea of doing work I'm not good at so I think it's time to call in the experts. I also don't do windows.

 

[wyreman]

They are 12" marble tiles.
No windows to do either, just power and light to a display case =)

 

[ggunn]

They are 12" marble tiles.
No windows to do either, just power and light to a display case =)

Is there any way to lift the tiles? If they were mine, I wouldn't like a scar across my expensive tiling. Better (if possible) to lift the tiles, trench the slab underneath them, and replace the tiles with access holes for the wiring. FWIW, the ceramic tiles near my front door are not stuck to the slab, they are just laid down and grouted.

 

[wyreman]

Tiler has replacement tiles

 

[Smart $]

Well to start with, if you go with UF, it is not permitted to be embedded in poured cement, concrete, or aggregate [340.12(8)]. Using traditional floor patch methods, you will likely have to go all the way through the slab.

Not enough info to determine GFCI.

How set are you or store on cutting and patching a groove. IMO even a quality groove and patch job would be unacceptable for a true high end store. With matching tile available, I'd just plan on having a flooring company fix the affected tiles.

I don't know all the conditions, but for a distance of ten feet, I would consider horizontally driving 1/2" GRC under the slab.

 

[Smart $]

Is there any way to lift the tiles? If they were mine, I wouldn't like a scar across my expensive tiling. Better (if possible) to lift the tiles, trench the slab underneath them, and replace the tiles with access holes for the wiring. FWIW, the ceramic tiles near my front door are not stuck to the slab, they are just laid down and grouted.

If it is known they can be lifted without a doubt, great. Otherwise better to plan on replacing all affected tile, IMO.

 

[Dennis Alwon]

I would not touch the marble. I would hire a person who works with the stuff and have them remove it. Marble is very fragile and breaks quite easily.

 

[wyreman]

the marble is not too big a concern as they will be redoing the whole ten tiles or so.
i was going to concrete saw a channel, not too worried if the rest of the 10 tile strip is impacted
then probably one more run with the dusty blade down the middle
and then cold chisel as needed to get a good bed.

i like the idea of the rigid but the question is how deep to chanel?
i may actually pass on the work.
i suggested overfloor raceway but this is kind of out of my area of expert
and i don't have time for this

thanks so much guys!

 

[Smart $]

... i like the idea of the rigid but the question is how deep to chanel? ...

No channel, per se. Jackhammer or otherwise remove a two tile area of slab on one end and a one tile area on other. Drive conduit under the slab from former to latter.

I've done this outside under sidewalk. Used plumbing pipe reducer with 3/8" nipple (IIRC) and an impact driver with ground rod adapter. Had plenty of clearance and minimal impact potential on surroundings. As I said, don't know all the conditions of your project, so don't take it as a recommendation.

 

[Cow]

Since this slab is in the middle of a store, how you do expect a guy to drive a piece of pipe under a slab when he can't get a piece of pipe started to shoot straight directly under the slab? Do you want him to bow it down into the hole and hope the curved pipe comes right up where he needs it? I wouldn't count on it. If they have to pull tiles to make the holes in the floor to drive the pipe through, they might as well remove all of them in a 10' stretch while they're at it. Then I'd have a trench cut wide enough to drop some 3/4" pvc in.

This way you know it's going to work and there's no screwing around.

 

[Twoskinsoneman]

How deep to cut a groove for uf cable
Code would want 4" and/or gfi it.

where are you coming up with that?

 

[jeremysterling]

... Then I'd have a trench cut wide enough to drop some 3/4" pvc in.

I agree with using PVC.

Experience has taught me that the worst part of this job is cleaning up the dust storm that will be created by saw cutting. Contrary to what some will say, water on the blade will NOT stop dust from going everywhere. Either build a containment room with plastic drop-cloths or hire an army of cleaning ladies.

Rent a walk behind, build the containment, cut the trench, lay the pipe(with stubs), backfill with grout (leave a quarter inch or so for the tile man to float his floor).

You can do this overnight with a helper. Use velvet ropes or other barricade until the following night when the tile man can finish.

 

[Smart $]

Since this slab is in the middle of a store, how you do expect a guy to drive a piece of pipe under a slab when he can't get a piece of pipe started to shoot straight directly under the slab? Do you want him to bow it down into the hole and hope the curved pipe comes right up where he needs it? I wouldn't count on it. If they have to pull tiles to make the holes in the floor to drive the pipe through, they might as well remove all of them in a 10' stretch while they're at it. Then I'd have a trench cut wide enough to drop some 3/4" pvc in.

This way you know it's going to work and there's no screwing around.

Have you ever impact driven in a 3/4" ground rod? How long did it take? Ever had to bow one to keep the top close to a wall? Very similar with 1/2" GRC. Have to stretch every conceiveable angle (pun intended), even chipping out bottom of slab under first to-remain tile... not to mention fabricating a pointed end for the conduit. The holes made in the slab I'm assuming would be under display case(s) or other side of partition wall, where basic patching would suffice, requiring little if any tile work. Underslab conditions will affect the straightness and ease of the drive. The decision to proceed is also very dependent on true slab thickness. If it's a go, have some extra sticks available, just in case the first try misses the target area. Worst case, have a saw ready to go.

I'm not saying its a risk-free method, but don't knock it completely unless you've actually tried it.

 

[Fulthrotl]

They are 12" marble tiles.
No windows to do either, just power and light to a display case =)

ok.... take a big block of dry ice, 12 x 12, and set it on a tile. with a little bit of luck,
it will pop the tile loose, without breaking it. mark them with duct tape,
showing the orientation, and position.

works well on mastic embedding, less well on thinset.

see about spare tiles. things happen.

after you get the tiles up, sawcut a 2" wide by 2" deep slot, not going
thru the slab, after making SURE it's not a post tension slab. put a 3/4"
PVC in the slot, and another one, for future data, tele, whatever.
direct burying ANYTHING where you might have to get to it again, is
asking for trouble.

pourock over it, trowel it out. let it set up an hour. re lay the tiles.

or, get someone who does this sort of thing, and let them have at it.
if you haven't done stuff like this before, a high end retail store is not the
best first classroom. you might want to let this one be done by someone
else, and make it their problem.

i had a commercial occupancy where we opened up a wall, and found a piece
of 12/2 romex disappearing into the slab. disconnected the power, and the
fountain in the middle of the lobby went off. gloss red subway tile, 25 feet of
it to the fountain..... they original contractor lost the run, so they laid romex
*in the tile grout*, zigzagging all the way to the fountain. snuck it by the
inspector, and ten years later, we get to remodel, and move the wall it came
up in.....

not a good day.

 

[hurk27]

ok.... take a big block of dry ice, 12 x 12, and set it on a tile. with a little bit of luck,
it will pop the tile loose, without breaking it. mark them with duct tape,
showing the orientation, and position.

works well on mastic embedding, less well on thinset.

see about spare tiles. things happen.

after you get the tiles up, sawcut a 2" wide by 2" deep slot, not going
thru the slab, after making SURE it's not a post tension slab. put a 3/4"
PVC in the slot, and another one, for future data, tele, whatever.
direct burying ANYTHING where you might have to get to it again, is
asking for trouble.

pourock over it, trowel it out. let it set up an hour. re lay the tiles.

or, get someone who does this sort of thing, and let them have at it.
if you haven't done stuff like this before, a high end retail store is not the
best first classroom. you might want to let this one be done by someone
else, and make it their problem.

i had a commercial occupancy where we opened up a wall, and found a piece
of 12/2 romex disappearing into the slab. disconnected the power, and the
fountain in the middle of the lobby went off. gloss red subway tile, 25 feet of
it to the fountain..... they original contractor lost the run, so they laid romex
*in the tile grout*, zigzagging all the way to the fountain. snuck it by the
inspector, and ten years later, we get to remodel, and move the wall it came
up in.....

not a good day.

And hope there is no other pipes or conduits embedded into the slab you are cutting, been there done that:ashamed:

I sure hope you have or can get a locator's to locate pipes and or conductors if there is PVC, and even water pipes.

We came into the aftermath of one electrical company who didn't do it home work and sawed right through 8 sets of feeders and some branch circuits doing some work just like this, it was a mess to chip out and reconnect all those pipes, and not to say they were thrown off the job because it shut down over half of a strip mall!!!

What ever method you use DO YOUR HOMEWORK!

 

[KWH]

Wire Depth

Wire Depth

Does the shallower depth apply with gfi protection on a commercial job.

 

[hurk27]

Does the shallower depth apply with gfi protection on a commercial job.

I don't think there is any such code commercial or in dwellings for conduit or conductors embedded into concrete, there is only an allowance for conductors where buried in soil as far as I know.

See table 300.5 and row "Under a Building" 0 0 0 0 0 all the way across, notice all cable methods state "in raceway only"

 

[wyreman]

where are you coming up with that?

looks like Table 300.5
allows conduit to be laid in with the rebar

 

[Smart $]

looks like Table 300.5
allows conduit to be laid in with the rebar

You said UF and 4", not conduit.