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Posted by David Sherman [72.47.9.228] on Tuesday, February 08, 2011 at 20:09:23 :
Thought I'd ask here just in case anyone has any ideas I haven't thought of. I would like to enlarge a hole in a concrete wall so it's big enough to get through easily and pass timbers through to brace the floor in the space on the other side. The hole basically goes from one large basement to another small one. It was cut after the building was built, but is just big enough to run a lot of pipes and wires through, with a little bit of room to slither underneath them. I want to cut the bottom of the hole down to the level of the floor in the smaller basement. If this was a modern basement wall made of 8" thick modern concrete, I'd just rent a gas-powered concrete saw and zip it out. The problem is this wall is 2-1/2 feet thick and the concrete was stuffed full of hard rounded river rocks, no doubt to stretch the concrete and because the river is right next to the building. I have a good roto-hammer with a 3/4" and 1-1/4" x 30" bit. I have gotten a few holes through it with the 3/4, and have tried two holes with the 1-1/4, but the bit jammed both times, probably because it caught the edge of one of those big rocks, which tries to force it sideways into the softer cement. The passage is about 2' wide, and I'd like to take the bottom of it down about a foot and a half or 2 feet. So, actually the thickness of the wall is greater than the width or height of the part I'm taking out. I probably won't try to make it any wider, both to maintain the support of the building and because it'll be hard enough to lower it.
Obviously if I had a laser fusion plasma light saber, I'd just burn a nice neat hole through it, but I don't have one. If I had a jumbo, or even a jackleg down in the basement, I'd zip a row of holes through it in about a minute per hole, put a few more in the middle, and knock out the chunks with a double-jack. Unfortunately I don't have either of them, nor a compressor to run one if I did.
Is there such a thing as a gas-powered rock drill that could maybe use regular hollow drill steels and water? I can get ventilation in there if I have to, and water can drain to the sump. How deep will the biggest masonry saw cut? Is there a diamond studded chain saw chain I can put on my Stihl? I'm reaching here. I'm to the point where I'm seriously considering blasting -- maybe drill 3/4" holes every 2" around the edge, drill a few more little holes in the middle, and load them one at a time with pyrodex. Hopefully it would crack the concrete enough to pry chunks out with a rock bar, but the cracks wouldn't propagate past the perimeter holes. Anybody tried this? Or maybe try Jerry rig something like a pin and feathers and drive them into interior holes to split chunks out.
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