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vsheetz 01-29-2009 01:22 AM

How-To: cut a channel in concrete?
My house is built on a concrete slab. I need to cut a channel in the slab to install electric to a new kitchen island. Need to fit a 3/4" PVC conduit - the length of the channel is about 5 feet.
  1. I was told that if it's a post tension slab, I cannot cut the channel - is this correct?
  2. How do I tell if it's a post tension slab?
  3. Suggestions on how to best cut the channel?

Ron6519 01-29-2009 05:16 AM

If it's that sort of slab, you will need another route or redesign the layout.

yesitsconcrete 01-29-2009 06:09 AM

the channel can still be cut,,, post tension cables're installed in the middle of the slab & run in 1 direction - your odds of being parallel're 1 : 1 or 50 - 50 :laughing: they're also install'd mid-point vertically.

How do I tell if it's a post tension slab?
look at the clap sides for patching cement - get a metal detector & ' sweep ' the floor

Suggestions on how to best cut the channel?
diamond blade as we cut all conc.

Willie T 01-29-2009 09:46 AM

The likelihood of your slab being post tension is very remote. It's a relatively expensive way to do a slab, and is generally considered unnecessary overkill in most residential construction. If you have no plans for your house to consult, try the building department. They keep records. Also, ask some of your neighbors. Chances are the houses in your area were built by the same contractor, and some of your neighbors may have plans.

Tscarborough 01-29-2009 10:40 AM

Probably 50% of the homes built in Austin in the last 20 years are post tensioned.

yesitsconcrete 01-30-2009 05:52 AM

hadn't realized the %age was that high, 'scar,,, expansive soils as in colorado ? ? ?

Clutchcargo 01-31-2009 11:15 AM

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For my own edification, what is a post tension slab?

Tscarborough 01-31-2009 01:21 PM

High carbon steel cables, coated with grease and a plastic sleeve are laid throughout the slab (although a whole lot less than normal rebar), with one end terminating into an anchor, and the other end left loose outside the slab.

After the slab is placed and cured, a machine is attached to the loose end of the cable that pulls it to a certain amount of tension. That end is then restrained, the excess cable is cut off and the hole patched. This puts the entire slab under compression, which is a very good way to prevent slab failure.

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