Concrete Coring

[Prashun Patel]

I would like to vent my DC outside. The only exterior wall is cinder block, though. What is the easiest way to drill a 4-5" hole? I'm thinking a whole bunch of little holes with a hammer drill.

[Fred Belknap]

What you are thinking is probably the best way. Drill several holes around the outside of the circle and one in the middle should do it. Blocks aren't very hard but use a masonary bit.

[Dan Hintz]

If possible, get the hole right between the support sections of the block... less material to remove, and more material to hold the house up. A hammer drill will work, followed by a chisel to smooth out the area in between. Don't forget safety glasses when chiseling, that stuff'll put an eye out!

[Bob Vallaster]

You can rent a hole cutter of proper diameter and the BIG drill needed to power it from a Home Depot store which has tool rental. Be prepared for sticker shock.

BobV

[Trevor Howard]

To add to what Dan said, check you are going through a "hollow" section. Depending on Building codes, every fifth cavity can be filled all the way up with concrete, for stability.

[Keith Outten]

Purchase a cheap air chisel from HF, it will make short work of cutting any size hole in cinder block or bricks.
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[Larry Frank]

I would drill a center hole all the way through and then mark the outside of the circle both inside and out and then drill the holes all the way around. You may be able to make a relatively neat hole that way.

[Phil Thien]

Just rent a Hilti (or similar) with appropriate core bit.

If you have any friends in HVAC they probably have the gear you need.

It will take ten minutes with the right gear. And be perfect.

[Ryan Hellmer]

I agree with Phil, no reason not to do it right.

Ryan

[Tom Hargrove]

Prashun -

I have used the "lots of little holes" method in both concrete as well as hollow block walls. The perimeter of the hole ends up a bit ragged, and if the outside of the hole lands on one of the webs in the block, the whole process (pun intended) can get kind of messy, (DAMHIKT). Much better to rent the proper equipment from a rental store if only to score the outside of the hole from both inside and outside. If the hole misses the block webs, and you choose a cavity that has not not been grouted/filled with mortar/concrete (not to mention rebar or a j-bolt), both of which would be good things, you can insulate the cavity with some "great stuff" foam when you slide the duct through the wall.

[Mike Cutler]

Either method works, but obviously the core bore bit would leave the nicest edge.

Someone has to be the party stinker, so I guess it will be me.
You "might" have to install a mortared thimble sleeve to pass through the wall to be compliant with some of those pesky building codes. I would ask first, because you may need to bore a 6" hole.
Sorry to be the party pooper, but I helped a friend install an oil fired furnace, and the Tank fill and vents had to transition through a thimble, so I kinda learned this on the fly.

[Mark Bolton]

I am not sure and I too dont want to be a stinker but there is more to coring a hole in a vertical wall than renting the core drill. This is not a hand held operation for a 4" or larger hole. You will have to set anchors in the wall to bolt the core drill to and then drill your hole. Its still the only way you will get a dead clean hole and will look (and likely make you feel ) the best and be a neat job. You would then have to remove/cut/patch the holes for the required anchors.

Not glory, but I am a GC and the only advice I would give you is as others have said, make sure to locate your hole in a core of the block _unless_ your hole is going to be larger than the core itself. If it is going to be larger than a standard block core (5" for a stretcher, slightly smaller for a sash-lock) its best to locate your hole right in the center web. Its very difficult to shave the webs open and much easier to just knock them out. One web is not going to affect the structure. If you go the hammer drill route mark your hole diameter 1/2" larger than your pipe because when you chisel the block out (if your not completely in a core) the hole _always_ gets smaller towards the center of the block. This is even more true with a poured concrete wall. Run the smallest bit you can (1/4" or so) and keep your holes as close as you can without drifting into the adjacent hole.

I think around here a core rental is about 60/day plus the bit. May as well plan on 100$ plus the couple anchors. It would be all setup for a 2 minute core job but would be nice.

You'd be doing something like this:
http://www.penhall.com/images/lightbox/CoreDrill.jpg

or maybe this:
http://www.aggregatetechnologies.com...ll-seawall.jpg

WOW

Mark

[Dan Hintz]

Check into the thimble Mike mentioned, just to be sure, but typically it's not necessary for going through a block wall, only wood. You're also not passing a fire-/heat-bearing pipe through, so it's even more questionable as to the need. Even the flue for our pellet stove runs right through the wall... a thimble is used on the inside where it will come close to the stud wall.