Trouble with concrete anchors

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Old 06-06-14, 12:24 PM
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Trouble with concrete anchors

I need too use concrete anchors in a masonry wall. The wall is made out of concrete block, that uses coarse quartz sand to fine grained quartz as a base. The sharpness of the rocks inside the blocks causes the bit to jump around and make an irregular shaped hole. The face of the block is not smooth and starting the hole is difficult. Also the quartz is extremely hard, making it difficult too drill through. I tried drilling into the mortar, but there is re-bar running though all of it. Which causes the bit to slide off the bar into the block; causing the same problem. I'm trying to hang a metal box that weighs about 15lbs. Thanks for the tips.
 
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Old 06-06-14, 01:24 PM
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Welcome to the forums! I've never seen rebar run in a mortar joint. How big a hole are you drilling? What are you using as a fastener? I would use Tapcon with a Tapcon bit. What type box. Reason I ask is electrical boxes such as subpanels take special fasteners in concrete. Box weighs 15 lbs. How much will the potential contents weigh?
 
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Old 06-06-14, 01:45 PM
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Thanks for the welcome!
It's a night drop-box for an automotive shop. It will never get much heavier than 15lbs(pending 8oz in paper envelopes and a key or two). I'm using 1/2" lead lag shields with a corresponding hole. Trust me, the re-bar was a surprise for me too. From what I hear the building was designed by the owner and built to his specifications. Is there way too check to see if the re-bar does run through all of the mortar? From what I've found I've hit it 3 for 3. I didn't want too do anymore exploratory drilling.
 
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Old 06-06-14, 02:12 PM
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If you are drilling in the mortar the "reinforcement" is just wires (1/8" - 3/16" diameter) from the joint reinforcement (not structural) and is within 1/2" of the face of the joint. It is continuous in a particular joint, but not all mortar joints and joint reinforcement (usually 8" to 24" on center vertically), so adjusting the height to a different joint would allow you to

You would be better off with a hammer drill for a lag shield hole in the block and you can "force" the hole location in the initial fractions of an inch. In the face of the block you would have to go about 2" deep to hit any rebar (probably 1/2" to 3/4" in diameter and that is spaced much more than 8" o.c., so it very remote you will ever hit rebar.

Dick
 
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Old 06-06-14, 02:51 PM
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The reinforcement wires are 3/4" thick. The drill I'm using is a BOSCH 11236VS hammer drill. The quartz rocks inside the concrete make the bit jump around erratically. They get "chiseled" out more often than cut.
 
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Old 06-06-14, 03:31 PM
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Drill a small hole first and then follow up with the larger bit. I sometimes have to step it up several times, but if it jumps as much as you say, you may end up drilling a smaller hole that will actually fit your lead shields.
 
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Old 06-06-14, 04:08 PM
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IMO, 1/2" is way too big. Tapcon using their equivalent 3/16" bit and Tapcon screws with a washer at the head.
 
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Old 06-06-14, 04:34 PM
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I think it has to be a very angular, very hard aggregate (crushed igneous rock) in a coarser textured block and not a block with finer texture or softer aggregates. - The large angled rock (crushed) will always tend to deflect a drill if it is hard. In that case, a small bit could also side before it can get something to bite on. Ultra strong block (6000-8000 psi) fine textured block drill accurately very well because of the finer, tighter aggregate. - There is a wide range of aggregates in block due to local availability and costs.

Drilling head joints (the vertical ones) could be the best choice, but the spacing may not fit the item to be mounted. The other choice is trying the joint 8" up or down from the layer that has the 3/16" wire.

Dick
 

Last edited by Concretemasonry; 06-06-14 at 04:52 PM.
 

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