What's a Good Way to Cut Holes Through Cement Blocks?

[Todd, KA1KAQ]

 Without breaking them, that is.

I'm in the midst of getting more work done on the garage/radio area which includes tightening up the gaps to the outside world. True, it means no more cool looking lizards hanging around the place, but it also means it'll be easier to heat in winter and cool in summer.

One of the biggest offenders of allowing in cold air are three foundation vents around the lower wall. These things are used to vent the crawlspace under houses to prevent mold and such. I'm guessing they placed them in the garage just to continue the aesthetics of the main house as they don't serve the same (or any) purpose in a 2 bay garage where doors are regularly opened.

The foundation is constructed of those half-thickness cement blocks on the inner wall with brick facing. I discovered that I could simply replace the inner missing block, remove the vent portion, and install the outside grill in the remaining space for appearances.

So I got three blocks, two are currently in place. The third needs a hole for a conduit to carry coax feedlines and a grounding cable through the wall. No problem, sez I. Out with the masonry bit and electric drill. I made a nice pattern of holes in each side, filled in gaps that were too wide with extra holes, then started carefully chiseling the remaining cement from between the holes. Stayed well away from the edges which would be weaker and likely to cause cracking. Well, it didn't help. About 2/3 of the way through removing the first cut out, *ccccccrack*.

I freely admit my ignorance in whatever else may be available for cutting holes in these blocks properly. But I like to do things myself whenever possible, not hire someone else to do it for me, so I'm always looking to learn. And as the photo shows, sometimes the Jethro Bodine approach doesn't cut it.

Aside from beating on an already-weakened block with a hammer and chisel, what else am I missing here? I'm hoping to get this last block completed soon so that I can move on to insulating some walls and adding more outlets. And fixing transmitters, of course.

[WA1GFZ]

Get an old skill saw because it will get a lot of dust in the brushes.
Go to home chepo and buy a fiber blade for cutting concrete.
They are cheap but they will cut through the block or mortar. Get a dust mask and safety glasses. Die grinder will also work if you have an air source.

[KA8WTK]

The local hardware store has a "chop" style cutter that will use to cut block like you have in half for a fee. They also rent it. It is the same thing you would use to cut brick like is used in a sidewalk. Some regular 8" and 10" block are made to be split in two. The center between the cells is hollow, not solid like the one in the picture.
I have split block before, but to really do it clean seems to be an acquired skill. Mine never come out real clean on the split end. The right tools and the acquired talent is probably the key.

Bill KA8WTK

[Steve - WB3HUZ]

Get a core drill with the correct size. Drill it and you're done.

[W1UJR]

Steve's right, see http://www.sunbeltrentals.com/equipment/category.aspx?id=s520

[KB2WIG]

' Get a core drill with the correct size. Drill it and you're done."


Yeaah, what he said....


ya can also rent 'em at places like the despot.


klc

[W1ATR]

What size is that hole? Looks like 4in. A 4in core bit is probably around $75 for a cheap one, and arbor for it another $45. This is all provided you have a healthy drill to run it. How about if I just drill out one of those blocks and mail it to ya?  

Short of all that. Without a drill, I would probably just cut it or break it in half, or roughly half, put it in the space, shove the conduit thru the leftover space, then mix up a pinch of quik crete and fill in the remaining couple inches around the conduit.

[WA1GFZ]

If you remove the block you can cut it then cement it back in with a PVC tube as a form in the hole. Renting a drill sounds a lot easier.

[Todd, KA1KAQ]

TNX.

I was originally thinking along the lines of a hole saw like you'd use for installing a door knob/latch. Didn't see any for masonry though, and chances are good that my little Makita hand drill wouldn't handle one anyhow, though it did drive the masonry bit through with no issues. If I were only splitting it, that wouldn't be a problem. Growing up around granite in Vermont I learned to use a bull-set and sledge. Cement blocks are just a bit more delicate.

The blocks are only $1.50 each, so it's not a great expense to buy another. But I must admit - with one hole already removed and the other part way out now, the thought did cross my mind that I could just stuff it in the hole and epoxy it together or whatever. I figured on just using expanding foam around the conduit to seal it up well since there won't be any load or pressure on it to speak of then trim off the excess.

We'll see what Home Cheapo has to offer tomorrow. They've done well at cutting long boards and window shades for me previously, maybe they have a big-ass drill press sitting out back waiting for something to do.  

[k4kyv]

What size is that hole? Looks like 4in. A 4in core bit is probably around $75 for a cheap one, and arbor for it another $45. This is all provided you have a healthy drill to run it

Why would you need a 4" hole just to carry some coax and ground cables? One or more 1⅜" holes ought to do the trick. I just completed this exact project this morning, through the concrete block foundation of the shack to accommodate the temporary above-ground coax line to the tower, plus the rotor cable that will operate the remote antenna tuner.

I looked specifically for a masonry hole-saw but nothing of the kind seems to exist.  I went to Sunbelt Rentals, but all they had was an 18" long, 1⅜" diameter auger masonry bit and HUGE MONSTROSITY electric impact drill to run it, something that looked more like a jack-hammer used to tear up street pavement, $44+ for 4 hours  rental.

Next, I tried Lowe's tool dep't, and found a Kobalt 1⅜" Porcelain Diamond Hole Saw, designed for cutting holes for faucet and shower head pipes through ceramic tiles, for $16.  The size is just right for 1" i.d. water pipe or rigid conduit. I wasn't sure how well it would work on a concrete block, and the guy at the tool dep't didn't have a clue.  I decided I could risk the $16, taking a chance that the thing would break or wouldn't work, but it made a nice, round, smooth hole in the block, cutting through the concrete like a knife through hot butter. It ought to, since porcelain ceramic tiles are made of a much harder substance than are concrete "cinder" blocks.

It fits into an ordinary portable electric drill.  The shank is about 3/8", so you need something heavier duty than a small 1/4" drill. The saw is fitted with a 1/4" auger to make a pilot hole, surrounded by the cylindrical cutting blade.  I pre-drilled a pilot hole all the way through the concrete block using a longer 1/4" masonry bit. Make sure to drill through the hollow part of the block and not through the web.  The hole saw is only about 1 1/2" deep, since it is designed for thin ceramic tile. I drilled into the block as far as the blade would go, which fell short going all the way through the outer wall by less than 1/3", then used a 1/4" diameter philips screwdriver inserted part way into the pilot hole to break loose the concrete core, allowing me to re-insert the saw to drill the rest of the way through the exterior wall of the block.  Then I crawled under the building and repeated the procedure from the interior side of the wall using the same pilot hole I had already drilled.

One thing I would do differently if I had to do another hole, would be to use measurements to determine the spot for the exit hole on the other side, instead of running a long masonry bit all the way through the concrete block from the outside. The interior hole ended up a little slanted downwards from the exterior one, despite my best efforts to maintain the bit level and perpendicular to the wall, and the conduit pipe wouldn't pass all the way through the first time. Using measurements and starting from scratch from the opposite side, I could have made do entirely with the short built-in auger that comes with the hole saw, and not have even had to bother with the long bit and both holes would have matched up.  I did manage to use the saw to erode away enough concrete on one side to elongate the hole in the appropriate direction so that the piece of conduit would pass all the way through to the other side.

[AB3L]

Could you build a frame to size with lumber? Say some 2"x2" wood screwed together. Lay it flat on top of plastic sheet, a little wire for support, and pour redi mix concrete into it with the conduit you intend to use installed. Shouldn't be too heavy and you can mortar it into place.

Otherwise, maybe you could contact a local electrical or plumbing contractor and have them use their diamond core bit with water to cut the size you want. Most larger contractors own their own set up and would probably do it for you.

I replaced basement windows with glass block. They make a cell with the 4" hole for dryer duct to pass thru. Maybe this could also be used in combo with a piece of block to fill the hole.

[KF1Z]

Hole saws for block should be readily availabe at home cheapo.

Although home cheapo is a pretty expensive place!


Could get one on ebay.

Tungsten Carbide.
$35. for the saw, and $17 for the mandrel.

---------
A note on cheap masonry / stone blades....

I bought 5 blades for my skilsaw for $50.
(I'll send you one if you want it for postage)

I am using them for Marble and Granite. I bought 5 because I thought I'd ruin such a cheap blade really quick in hard material.
But to my suprise, I haven't even used one up yet.
I've made almost 30 feet of cut in 1 1/4 " thick Marble !

Just keep the water flowing.

[WQ9E]

Put the block in your truck or trunk and drive to a home construction site where a plumber or HVAC truck is parked.  For a very small fee I am sure one of the tradespeople will fix you up.

[Todd, KA1KAQ]

Why would you need a 4" hole just to carry some coax and ground cables? One or more 1⅜" holes ought to do the trick.

In my case here Don, the plan is to use a PVC coupling sealed into the block, with a short piece of pipe passing through the now-decorative-only screened vent cover to the outside world, with a 45 degree elbow added there. The reason being that my aerial farm has yet to take shape beyond a couple dipoles. Since the situation is still quite fluid in that respect, this approach allows more flexibility over the short term. Making a series of small holes would mean having to crawl down under the operating table to bore another hole each time I add a feedline, or blowing a bunch through and having to seal them temporarily. This way here, I can just snake a number of coax lines through along with a good, stout ground cable and not run out of space. One of the guys locally has a machine shop and has offered to make me a nice bulkhead on a large copper plate which will accommodate not only coax connectors but also open wire feeders when the time comes. The cement block is just meant to be a stop gap measure to allow some flexibility in the meantime while also sealing up the garage wall.


A lot of good ideas for sure, some like the wooden frame and glass block dryer vent sound perfect. Others are a bit more....complex for my situation here.    This is what makes the site so great - the variety of ideas and experiences to draw from. Thanks again to all.

[W3GMS]

Todd,
When I was finishing off my downstairs, I wanted to bring a 4" PVC gray electrical conduit through my foundation wall.  A local Ham came over with what I believe to be a diamond tipped hole saw and drill.  It was a one piece assembly that we bolted to the inside of the wall.  The fasteners are still in the wall!  He borrowed it from where he worked for the weekend.  It worked great and did not take long to do.  I believe it had threaded fine pitched threaded rod as part of the tool to lead the drill into the hole being cut.  If you can find someone that rents such an animal that would do the job for sure.  Some sealer around the electrical conduit and its a done deal.  The trick is to find someone that rents that type of gear.  Very heavy duty stuff. 
Regards,
Joe, W3GMS     

[W3SLK]

Dot-out the profile of the transition piece and rent out a Hilti hammer drill. The absolute best drill for drilling into cinder block or concrete, (at least in my opinion).

[W1ATR]

Yeah core drilling rigs. Very cool.

We did a large city job a bunch of years ago and we had to pass two 16"X30" runs of ductwork through a 14" thick concrete wall. The logistics of doing that to the foundation of a 75yo 8 story building are ridiculous. After 2 weeks of the engineers arguing with each other, I hired a company to come in and shoot the holes. They drilled 8" holes in the corners I marked out with a core rig, the switched to what basically amounted to a special chainsaw that had a 30" bar with a diamond chain on it and went hole to hole making nice smooth straight edges. Long story short, after the $5000 layout to change the blueprints, pay the engineers, have hot coffee and donuts on hand every time the inspector showed up, and hire the coring company, I had two nice holes to run my ductwork thru.

  

[Bill, KD0HG]

The best idea here if cost is important is to replace the block with a piece of 2" thick wood plank. Mortar it in place. Then caulk. You can then abuse it all you want using cheap bits.

[Todd, KA1KAQ]

Which never even dawned on me, Bill. I even have a piece of pine plank out in the other garage. I opted to piece the block back together since it was pretty much cut out and ready. Will add the PVC, seal around it and install. I will eventually just carry the ground cable but will serve double duty for feedlines in the interim.

[WA1GFZ]

Wood will just rot and attract bugs. How about that fake plastic wood. A couple layers and it will never rot.

[Steve - WB3HUZ]

Plexi?

[k4kyv]

Or polycarbonate.  Other than questionable claims about its resistance to UV damage (which shouldn't be an issue here), the stuff is almost indestructible. You can practically pound it with a sledge hammer and it will survive. 1/2" thick sheets are relatively inexpensive, but the cost becomes prohibitive once you go to 1" and thicker stock.

[WQ9E]

Since what you are cutting is relatively thin wall concrete, a Rotozip tool with a masonry bit and the circle cutter attachment would also work.  I picked one up when we were doing a house addition several years ago to do some oddball cuts in concrete backer boards and found it also did a good job with plumbing cutouts in thick tile.  It doesn't zip through concrete like a hammer drill but the cut is very smooth.

If you have other projects coming up this is a handy tool to have around and I used it a lot last year while putting in a central vac system.  It can make regular and irregular cuts in areas where limited access makes use of other tools difficult.  Since it is a rotary instead of reciprocal action it is easy to guide and is less likely to cause collateral damage since the cutting depth is easily and precisely controlled.

[Todd, KA1KAQ]

That sounds like what I was looking for, Rodger. Obviously didn't search for the correct term. Looks like it would be handy to have on hand for future jobs. The blocks they make today seem a lot more brittle than years ago. Probably varies by the batch, like anything else.

[Mike/W8BAC]

Todd,

If you settle for wood or plastic you might think about making a grounded bulkhead while your at it. Find a 1/8" thick piece of plate copper and mount coaxial bulkhead fittings to it and ground it just outside the shack to a ground rod. It's a great place to mount PolyPhasor protection. Add extra feed trough's for the future.

Mike