drill holes in concrete

I'm working on a retianing wall project that involves using busted up old concrete slabs. I need to drill a ton of 3/4" - 1" holes as the blocks get higher, any ideas? Also ideas on how to crack the 4" thick concrete where I need to? Do you think a peice of angle iron and a sledge is best?
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I
Holes, either a "hammer drill" with a "carbide bit" or a "regular drill" with a "dry diamond bit". For cutting the concrete where you want it to crack. Why now just use a "diamond blade" and a "circular saw" and just cut it?
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a decent size hammerdrill will make the holes with no problem, but if you drill too close to an edge, the slab may break off. Depending on the thickness and strength of the slab pieces, you may need a setback of 6" or more.
If you want reasonably straight edges, it would probably be best to score the smooth side of the slab with a wet concrete saw and then break with a hammer.
ps Seems like an awful lot of work.
Bill

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the slabs are 4" think. What works better a hammer drill and masonary bit or a diamond dry bit in a regular drill?

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I've never used a dry diamond bit before but a hammer drill with masonry bit should make quick work of this.
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A hammer drill, for your application. It will go through concrete like butter. The composition of the aggregate might give you some difficulty, though. Very hard gravel pieces are tough on the best drills.
-Frank
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A hammer drill with the appropriate bit will go thru the concrete quickly.
Go rent one from the local rental shop. A homeowner's drill, even though it may have hammer capability, is not up to the task.
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or
Dry Diamond with a regular drill will work better than the hammer drill with a carbide bit. The diamond won't "blow out" the back of the slab when you exit the slab. The hammer drill will "blow out" the last bit of concrete and make a larger exit hole. Dry Diamond blade for your circular saw will cut through the slab with no problem. If you want to make it easier on the saw, just cut one inch depths with every pass till you are all the way through.
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wrote:

Neither. A rotodrill sounds much faster and better, according to a thread yesterday. You can rent one.

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wrote:

It's interesting how it sometimes (not too often) makes a difference when one posts and who answers.
I only recognize one or two names in the answers here, and I don't think any of them answered in the thread yesterday, where 2 or 3 people were very convincing that a Roto-Drill, or something like that, was far better than a hammer drill.
Although there are weaker "consumer" versions of hammer drills, there are none afaict of Roto-drills, so you surely have to rent one, and it is will worth it since you have to drill a ton of holes. (How many holes in a pound?)
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get
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Well, I often core 3/4 - 4 1/2" holes through concrete, block, cidar block, and rock. The diamond bits kick ass!
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Do you use a hammer drill with a diamond bit? or is a hammer drill used with a carbide bit?
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with
You didn't read my post carefully, so here it is again: "either a "hammer drill" with a "carbide bit" or a "regular drill" with a "dry diamond bit"."
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wrote:

If you have that many to drill, you want a rotary hammer and appropriate bit, not a hammer drill. They both work by apply repetitive impacts inline with the bit while it is turning, but the rotary hammer applies a much more forceful impact. The rotary hammers require a special shaft on the bit, of which there are two or three common styles. You can do this with a hamme drill, but the rotary hammer will drill 3-4 or more holes in same time the hammer drill will drill 1.
Go to www.toolsofthetrade.net and select the tool test archive. They have reviews of both hammer drills and rotary hammers.
If there is rebar in the concrete, you will need a bit designed to handle it, because you are sure to hit some. (And if there is rebar, your efforts to cut it or break it are going to be very frustrating...)
HTH,
Paul
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