Alwayslearningelec
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- NJ
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- Estimator
About how long could you do one through a 6-8" concrete slab? BTW, we sometimes need to have a guy coring and one on the floor below.
8" Core Drill
- Thread starter Alwayslearningelec
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- New Jersey
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- Journeyman Electrician
Depends partially on the size of and how much rebar. Should be able to drill that hole in an hour.
Alwayslearningelec
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- NJ
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- Estimator
Also never know when X-ray of slab is needed when coring or trenching concrete . Sometimes specified or notes on drawings and sometimes not.
How would rebar cause an issue ? Sure it would just curious in what ways
busman
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- Northern Virginia
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- Master Electrician / Electrical Engineer
What is the hole diameter, or did I miss that?
Mark
Mark
Alwayslearningelec
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- NJ
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- Estimator
8”
electrofelon
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- Cherry Valley NY, Seattle, WA
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- Electrician
The coring itself once all set up goes generally quite quick. I would say 6-8 " deep is only going to take 5-10 minutes of actual drilling. The setup is what takes time:. Setup can take an hour if you have to be real clean, need a super accurate location, have to find water, move stuff, etc.....
electrofelon
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- Cherry Valley NY, Seattle, WA
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- Electrician
But yeah I would agree with the others and on average budget an hour per hole.
- Location
- New Jersey
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- Journeyman Electrician
The diamond core bit cuts fairly quickly through concrete but it cuts very slowly through rebar especially if you have #8 or larger rebar. I've core drilled hundreds and hundreds of holes and the most important thing to do is to use as much water as possible. Guys often scrimp on the water which causes the bit to cut slowly and bind up due to the debris not being flushed from the hole. Then when they get the bit stuck they might spend an hour or so just trying to get it out without damaging the hole, that's if they can even get it out (that's another story).
We once cored over a hundred holes in a building lobby where we had access to a spigot and a garden hose. Those were some of the fastest holes we ever drilled.
synchro
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- Chicago, IL
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- EE
Concrete is quite strong in compression, and it comes in various compressive strengths. But it is weaker in shear, and is quite weak in tension. In comparison, steel rebar is quite strong in tension, and the pattern on its surface engages with the concrete to bind it together during tensile forces.
In some places undergoing tensile forces such as the bottom of a concrete beam, the rebar plays an essential role
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Alwayslearningelec
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- NJ
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On another note but similar. Concrete floor chopping for conduits. If you have say 1",1-1/4" and 1-1/2" conduit and need a 12" wide trench how long per ft. would you say?
make sure to be careful when drilling on suspended surfaces inside of buildings. we had a job at a grocery store where GC didn't check for utilities or Posttension cables in the slab. It cost them over $500,000 after smacking through 5 of them and figuring out what they were. Make sure to call in locates or x-ray before preforming the work. older buildings are notorious for hiding utilities in slab.
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Alwayslearningelec
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- NJ
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- Estimator
Thanks. Why so much $$?
These cables run through the slab all the wat to the other side to compress the concrete. the compression of these cables "post pour" add strength to the floor. often if these are hit they have to either repour that section and dig out those lines. Not to mention that there can be bundles of these together. imagine how difficult that can be, while avoiding all the rebar, all the way across the pour.
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