Breaking up concrete

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Our house has a flower bed immediately in front of the foundation. There's a patch in the flower bed that has no significant plants growing in it, and we decided to add some. When we tried to dig a hole to plant them, we discovered why there aren't any plants there:
It seems that someone had some leftover concrete, perhaps from pouring a stairway nearby that goes from driveway level up to front lawn level, and they simply dumped the excess concrete into the area that would eventually be the flower bed. There is a chunk of concrete about 6 inches thick, 6 feet long, and 2.5 feet wide in there, with a few inches of dirt over it. The concrete is not attached to the foundation or the sidewalk, it's just lying there. But it's too heavy to move as a single piece.
So I've been breaking it up into smaller pieces, using a single-point concrete chisel and a 3 pound club hammer. This just doesn't work very well for breaking 6 inch thick concrete. I end up holding the chisel in one hand and the hammer in the other until I get the chisel embedded far enough to stand up on its own, then I switch to two hands on the hammer. Sometimes this works in a half-dozen strikes, sometimes it never works and I try moving the chisel somewhere else. I've probably spent a couple of hours on this already, and it's down to half the original size, but progress is discouragingly slow.
The two ways to improve the situation seem to be: get a bigger hammer (e.g. a long-handled sledgehammer), or some sort of power hammer. What would be suitable for 6 inch concrete?
    Dave
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1) You can rent an electric jack hammer from any tool rental place. They are fairly inexpensive to rent and I think should probably work.
2) You can use a 4x4, or a strong crow bar, or something similar, as a lever to raise one end of the concrete up. Then place something solid under the raised piece of concrete. Then hit the concrete with a sledge hammer. When the concrete is embedded in the dirt, hitting it with a sledge hammer probably will not break it, but when it's raised up a few inches, hitting it will cause it to crack and break.
3) You can dig a deeper hole next to and under the remaining piece of concrete and just bury it deeper into the ground where it is.

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Read t his post after I typed mine -- honest!
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Though I didn't mention it, I'm already doing this. Using a heavy shovel and a digging fork, I've been prying up one end of the concrete and putting a rock underneath it, a few inches back from the end, so that the concrete is unsupported at the end and stresses in the concrete are concentrated around the rock. Without that, I would have gotten nowhere with the hammer and chisel.
It seems the most common recommendation is to just get a bigger hammer and hit the concrete with it directly, forgetting about the chisel. So I think I'll try that.
Thanks for all the suggestions!
    Dave
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writes:

Call the police and tell them John Wayne Gacy rented the house years ago and your smelling something foul coming through the concrete. You'll have a crew there in no time.
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snipped-for-privacy@cs.ubc.ca (Dave Martindale) writes:

An electric hammer from a rental place will make short work of it. About 10 minutes.
I'd go for a bigger hammer/chisel but if you want to get rid of it quickly, the electric hammer is all you need.
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Friends tell me to hold the electic jack hammer away from your body. If you lean it against your body while it's running, you'll hurt yourself.
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Yeah, now you tell me.
Actually, I did a large patio and didn't pay much attention to how I held the hammer. I had bruises all over my legs but didn't notice much pain. Must have been too tired to care.
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Oops! I'll try to do better.
Oh, be sure to use two hands holding a Sawzall, so you don't cut the index finger off your left hand. You'll need to know that in about two years. I didn't want to be late again.
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On Apr 4, 11:26am, snipped-for-privacy@cs.ubc.ca (Dave Martindale) wrote:

Yup, Dave, it's time to upgrade your tools for something that thick:
http://depave.org/index.php/how-to-depave /
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This animation link posted by "Mike" below is useful:
http://www.cornerhardware.com/howto/ht010.html

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On Fri, 4 Apr 2008 18:26:27 +0000 (UTC), snipped-for-privacy@cs.ubc.ca (Dave Martindale) wrote:

The bright side is you have half of it out already.

Try to lever one in up and place a brick, rock, lumber or such to hold the concrete off the ground. Then try a sledge hammer. I would try to break into two pieces - across the middle, then see if they are manageable.
If you have a hammer drill and masonry bit; drill a few relief holes across the center. Try the sledge again.
A rental unit will only take a few minutes to break it up:)
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On Fri, 4 Apr 2008 18:26:27 +0000 (UTC), snipped-for-privacy@cs.ubc.ca (Dave Martindale) wrote:

Get a large wedge (or two) and a sledge hammer. A jack hammer would make quick work of it too, but you still have to haul it out and away. Protect your back, lift from the knees and never twist the body and lift. Get a teenager or two to help you.
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wrote:

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On Fri, 04 Apr 2008 19:42:38 -0500, snipped-for-privacy@aol.com wrote:

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Except brick wall don't talk back.
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On Fri, 4 Apr 2008 21:46:38 -0700, " Frank"

I call that Silent Contempt.
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Like talking to a brick wall wearing an ipod?
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On Fri, 04 Apr 2008 18:01:35 -0400, Blattus Slafaly 0/00 ? ? ?

Read the thread, did you?!
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wrote:

I read it too, but see nothing that indicates a back hoe would not work. What did we miss?
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