Cutting a hole through 7.5" Concrete slab for registers


Old 07-10-19, 02:01 PM
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Cutting a hole through 7.5" Concrete slab for registers

I have a section of my house that was an addition and for some reason, they used a poured concrete slab on piers over an unfinished basement for the flooring material. The slab is 7.5" thick. I have to figure our a way to drill a square hole through that thick of a slab in order to run vent registers through. I'm nervous about using a jackhammer or rotary chisel because I'm worried the vibrations or shock impact could cause the freshly laid marble tile surrounding the area to crack (I wasn't aware that the A/C was going to need to be run through the floor otherwise I would have done this before laying tile.

If it was wood, I would drill 4 holes in the corners of the register box hole then use a sawzall between them; however, I'm not aware of a sawzall large enough to cut through 7.5" of concrete.

Any help / recommendation would be greatly appreciated!
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Old 07-10-19, 02:15 PM
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I'm not advising you do it because you could very well compromise the structural integrity of the floor, but this tool would do the job:

Seems like there could be another way to ventilate that area?
Old 07-10-19, 03:29 PM
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The tool mossman linked to is not the best tool for the job since overcutting the hole would weaken the floor. The best tool would be an ICS diamond chainsaw, if you can find someone who rents them. They can cut a perfect cube out of concrete. That type of saw enables you to plunge cut the ends. You do need to hook a hose up to it and having a second person there to run a wet vac is a must if you don't want a holy mess.
Old 07-15-19, 10:56 AM
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Yeah I can't use a round blade because it would cut past the square hole I need. That diamond chainsaw woudl be perfect....finding a rental is the trick
Old 07-15-19, 04:03 PM
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Another option, I rented a big hammer drill to set 5/8" dia anchors for my new shed and was amazed that that think would bore through 6" of concrete in about 2 min per hole!

Dozen holes around the perimeter and a pneumatic chisel and you have a square hole!
Old 07-16-19, 03:46 AM
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Marq's method would be the best option IMO.
I would suggest using smaller diameter holes.

Draw the outline of the hole you need and drill several holes with a concrete bit and drill.along the line.
The more holes you drill the easier it will be to remove the center portion and the less impact it would have on the rest of the slab.
Holes speced an inch apart or closer and in the center portion would make for easy removal.,,,,,,,swiss cheese comes to mind!

If you rent an SDS drill and bits the trip to the rental store will take longer than making the hole.
Old 07-17-19, 05:51 AM
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Hi, how big of a hole are we talking ?
Old 07-22-19, 06:02 AM
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I ended up paying a company called IDS to core drill the hole. I found round vent registers that would work. The 2 holes cost me $250 for them to drill. The slab was 8" thick and the 2 hole sizes ended up being 8" & 7". Attached is a picture of the core they drilled out
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