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Red Squirrel 04-27-2010 10:40 AM

Making conduit hole in raised cement floor
My garage is on a "raised" cement floor (has a crawlspace) and I'm thinking of running a sub panel to it, and maybe even some plumbing for an utility sink in the future. What would be the best way to make a clean round hole, maybe 8 inches diameter without causing any structural issues? The slab sits on cinder blocks and has a beam in the middle. I'm unsure how thick it is, I am guessing a foot or more. It looks quite heavy duty. The hole would most likely be at one of the corners. Is there issues with this? What type of tool would i use to make such hole? I'm thinking something like what is used to make door knob holes, but bigger and for masonry.

My alternate route is to run this stuff outside. The water would be more tricky though.

brownmoose 04-27-2010 11:29 AM

Making access holes shouldn't be too big a problem. You can use a 1/2" masonry drill bit and drill small holes all around the area that you want to punch out. You will probably have to cut a couple sections of rebar/iron support. Using a jack hammer might make it easier to make the hole but might lead to cracking beyond the area you want opened. Not easy to do cleanly DIY. This should not create any structural problems if floor is reinforced properly - just don't do it right above the beam. But... 8" hole seems about 2x to 3x too large. Just drill hole for exactly what you need. 2" for sink drain - 1 1/2" for wire conduit. For sink - if unheated crawlspace - you should be running the plumbing underground as running it in Ontario in unheated crawlspace will lead to frozen pipes.

Red Squirrel 04-27-2010 11:38 AM

Actually was thinking that too, am I better off with 3 holes that are smaller vs one big one? Also do some bits cut through rebar as well?

Mind you this is a small enough job for someone with the right tools, I could always just get someone to do it. By the time I rent the tools required and what not, it may cost nearly the same, if more.

brownmoose 04-27-2010 12:06 PM

You could probably hire someone to drill the holes fairly cheaply. Having made holes for chimney in concrete basement walls - it isn't easy. Had to drill bunch of holes. Some didn't go all the way through due to rebar. Then I pounded out the concrete once I had holes all around it with sledge hammers and chisels. Then I had to cut the rebar. Really a big pain. Doable though but you will need a good, powerful hammer drill.

jogr 04-27-2010 02:30 PM

The only way I'd run water to it is using a frost proof spigot through the wall from the house so that the valve end of the spigot is within the heated envelope of the house. You can even get Hot & Cold double frost proof spigots if you want both hot and cold water. If you will only ocassionally use the sink I'd consider just putting the frost proof spigot(s) in high enough that you can slide a laundry type sink under it and slide a 5 gallon bucket under the drain. Codes probably will allow you to install an "outdoor" spigot in your garage without a sink or drain (check). The sink and bucket would not be a permanent install, just a handy way to catch water from the spigot when it's not being used with a hose.

I'd be reluctant to drill any holes through a suspended stress slab without getting the ok from an engineer. I'm sure it can be done but it's no place to play trial and error.

stubits 04-28-2010 06:34 AM

I need to do something similar in the near future and plan on buying one of these or one of these.

I've read good things about them.

oh'mike 04-28-2010 06:53 AM

You might be better off hiring the work. We use a diamond core drill to punch nice clean holes into factory floors. The drill,with its water pump is very pricey--as are the diamond core drills themselves.

Look in the yellow pages under-concrete core drilling.

I'd make several smaller holes,rather than one big one--Mice like the big holes.---Mike--

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