Opening a hole for a window

In order to install a window in a concrete block wall, I would need to cut a hole in the wall.
What is the proper way to create such a hole? Do I chisel out a "rough" opening that is not exactly square and plumb, then build it back up with new concrete?
Or do I find a way to cut the rectangular hole precisely with specialty mansory saw?
Thanks in advance,
MC
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on 9/16/2007 3:12 PM MiamiCuse said the following:

They have a circular saw especially made for concrete work like this. Check with a concrete installer in your area and pay to have it done right, or rent the saw and mess it up yourself. :-)
--

Bill
In Hamptonburgh, NY
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Prepare to cry when you write the check. Here in SW MI a couple of years ago, a 12"x20" hole through the top edge of a poured foundation, right under the sill plate, cost me around $250. And they didn't even put a tarp down for the dust, or clean up. (Idiot previous owner that put on the addition out back didn't bother to run ducts out to it, or leave a chase at the border between old basement and new crawlspace. When I replaced the 45 year old furnace, I also tore out the wall furnace in the addition, and added it to the system, so I could get A/C out there.)
But for the OP- you need more than just a hole- you also need a lintel or header of some sort above the window, to carry the weight of the block above, plus any upper stories or roof structure that rest on it. Way too many variables in how block walls are constructed to give advice sight unseen- it may be trivial, it may be an expensive pain in the ass. It is worth the several hundred bucks over just renting the saw yourself, to have an expert look at it. Any custom masonry company that does commercial work will have the know-how to advise you, or point you to the outside engineer they use. IMHO, I would definitely hire the work out.
aem sends...
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I did hire the work out. Cost me $275.00 so you were pretty close. I did not like what I got, that was why I posted and asked - I was expecting a nice rectangular cut. This is what was done:
http://i173.photobucket.com/albums/w67/143house/framing/P1010366.jpg
I am not too happy.
Thanks,
MC
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Please tell me that there is a beam at the top of that wall, and the block isn't really structural. That looks like crap- I see no saw edges- looks like they did that with an air hammer. But the hole can be cleaned up and edged by a good mason, which you will need to call in anyway to cut in a lintel over that opening. Even if the wall above doesn't outright collapse, it will crack, and the cracks with telegraph through the stucco or plaster or whatever covering the block.
aem sends...
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Yes there is a tie beam above it. I need to find a good mason.
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On Sun, 16 Sep 2007 15:12:24 -0400, MiamiCuse wrote:

Rent a saw. Masonry saws are cumbersome, noisy and create lots of dust. Wear a respirator and old clothing. Ear protection, too.
1. Mark opening on wall with crayon or sharpie. 2. Make a 1/4" cut with saw to outline opening. Keep the lines as straight as possible since this will be your template as you saw deeper. 3. Deepen cut with each pass. Make several passes so you can control cut and line. Doubtful that saw will cut all the way through wall. You will have to mark the other side and follow step #2 again. To minimize mess indoors, you may find it to your advantage to block off area with plastic. 4. You have to determine whether you need a steel lintel or wood header for the opening. You can also figure out if you need to frame opening with lumber.
Most of this is common sense.
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I had to cut an 8" block wall to install a basement door and ended up renting a concrete chain saw which uses a diamond chain on a 16" bar. The process is a wet process and by hanging up some drop cloths I had no (that is correct, no..) dust. the wet swarf from the saw stuck to the drop cloth. Total cost was around $400 for one day and the process took less than an hour. The basic procedure was to, carefully, lay out the opening on the wall, perform a plunge cut with the chain saw through the wall until it is completely through the wall and follow the lines. No overcuts and the opening is absolutely square. I seriouly thought about cutting up the rest of the wall as it was do easy...but realized that I had to show some kind of control over my emotions. But it was the coolest... I realize that it was a bit pricey as opposed to a standard rotary concrete saw, but the clean up was minimal and the operation was fast and easy. My own attitude is that lack of dust alone was worth the extra bucks.
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