A concrete core drill is a diamond barrel bit on a motor, run down a mast that is bolted or vacuum held to the slab. The rig itself hires for about $75 to $150 a day. The cost people miss is the bit, because yards rent the barrel and bill the wear by the inch of concrete cut, so a rebar heavy slab is dearer than a clean one.
Handheld or rig mounted
Up to roughly four inches, a handheld drill with a clutch will do it, and the clutch matters because a bit that grabs will otherwise take your wrist with it. Above that diameter the mast is not optional. A rig holds the bit square, feeds it evenly and gives a hole that lines up with what has to pass through it.
Anchor bolt, vacuum base or jack post
An anchor bolt into the slab is the strongest fixing and leaves a small hole to patch. A vacuum base is quick and needs a smooth, dry, sound surface plus a pump running the whole time, so it is no good on rough or wet concrete. Overhead and wall work uses a jack post braced to the deck above.
Water, slurry and where it goes
Wet coring cools the diamond segments, flushes the cut and keeps dust out of the air, and it needs a hose at working pressure. What comes back is grey slurry that will run wherever the floor falls. A slurry ring and a wet vacuum are separate hire lines and are cheaper than cleaning a finished floor.
Rebar, depth and how long it takes
A clean six inch core through an eight inch slab takes a couple of minutes. The same core through two mats of rebar takes several times that and eats the bit, which is why the wear charge exists. Ask for a bit specified for reinforced concrete, and scan the slab before you drill anything post tensioned.
Questions people ask about concrete core drill
Can I core drill without water?
Dry coring is normal in block and brick with a bit made for it and a vacuum pulling at the shroud. In poured concrete, dry cutting shortens the bit sharply and puts respirable silica dust into the air, which has its own control rules on any worksite. If it is concrete, run it wet.
How deep can a core drill go?
The standard barrel is around fourteen to eighteen inches of usable depth, and beyond that the rig takes extensions on the same thread. Deep holes need the barrel withdrawn to clear the core and the slug removed in sections. Tell the yard the wall or slab thickness when booking so the extension comes with it.
Do I need to know where the rebar is first?
For a slab on grade, a bit rated for rebar will get through it. For a suspended slab or anything post tensioned, scan it, because cutting a tendon is a structural failure and a serious injury risk in one moment. Scanners are hired from the same counter and cost less than the repair.