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I have a predicament, I am putting up a shelf into the wall.

The wall is plaster, and then hollow and then concrete. I have screws with toggle bolts on them.

The 2 inch screw with the toggle bolt was too short to get the toggle bolt inside the plaster to the hollow part.

The 3 inch screw with the toggle bolt is too long because it hits the concrete. But the toggle bolt will reach into the hollow part.

How do I approach this dilemma? Do I need to drill into the concrete somehow? I think my current drillbit is incorrect for doing this, but I'm not sure.

Insight appreciated

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Are the toggle wings too long to open up inside the gap in the wall? Stick a small object through until you hit the concrete, and mark off the distance. If your measured distance minus the plaster thickness isn't longer than the toggle wings, then you need a different bolt or you need to drill out the concrete. Otherwise, you can do as dbracey suggests and cut the 3" bolt down to between 2 and 3". –  Doresoom Mar 8 '12 at 19:13
    
what tool would I use to cut the metal bolt? also, even with the 3" bolt I had to wiggle the toggle bolt in one side at a time, because the concrete was too close. I'll measure –  cqm Mar 8 '12 at 19:15
    
If you have a dremel with a cutoff wheel attachment, that would work. Otherwise a vise and a hacksaw could do it. –  Doresoom Mar 8 '12 at 20:37
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Find a stud, problem solved. –  Tester101 Mar 11 '12 at 13:49
    
@Tester101 That solution is way too simple. We need to add at least 5 steps, one of which requires kayaking to Alaska. :) –  Doresoom Mar 12 '12 at 15:31
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3 Answers

Are you comfortable with cutting the bolt to a length between 2" and 3"? That would be simplest.

Another possibility would be to use another piece of wood between your shelf and the wall to create more thickness for the 3" bolts.

If the concrete is actually concrete block, you can drill into that quite easily with a masonry bit from your local hardware store. If it is an actual poured concrete wall, best not to bother.

ADDED:

To shorten the bolts:

A) Take the bolt to a hardware store, tell someone you want the same bolt but in a 2.5" length - this is likely the easiest thing.

B) Cut the bolts:

  1. Thread a nut onto the bolt and spin it back towards the head.
  2. Use a hacksaw to cut the bolt (if you clamp it, clamp on the nut and head - not the threads) - OR - use a Dremel with a cut-off wheel - OR - use boltcutters!
  3. Unscrew the nut from the bolt; this will clean up the damaged threads where you cut it.
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how can I tell what material it is? I can only shine a flashlight through the hole and see there is something hard there that is not wood. The outside of the building is bricks with concrete in between the bricks –  cqm Mar 8 '12 at 19:12
    
If there is a big hollow space I don't think you want to screw into the concrete - there will be a lot of shear force on the screw and it might not hold it since it's not designed for a large gap between load and the surface its being anchored to. Cut the screw to the desired length instead and stick with the toggle. –  Steven Mar 8 '12 at 19:18
    
what tool would I use to cut the screw –  cqm Mar 8 '12 at 19:26
    
I think he's proposing just making some room for the ends of the bolts, and still using the toggle - not screwing into the concrete. –  dbracey Mar 8 '12 at 19:26
    
See added lines in the answer above. –  dbracey Mar 8 '12 at 19:27
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I had similar situation trying to install curtain rod hooks on the wall with thick sheet rock, hollow space and concrete block.

For the screw length issue - The guy at home depot matched the screw from the toggle bolt package by thread count to the sheet metal screws and picked the right length. This gives more choices.

My case was bit worse. I didn't have any screw length for which the toggle will open. The wing length was simply longer the the hollow space. I am posting couple of things I tried just in case.

For half the hooks, I took a sharp chisel and took out bit of inside edge of the sheet rock (through the hole drilled for the toggle bolt) up and down. I took out enough so the toggle will open if inserted vertically. With much difficulty I twisted it around to be horizontal where the sheet rock edge was in fairly decent shape and tightened it.

Since this was getting messier, I tried to cut the toggle wings bit shorter with a snip so it would not get stuck in the sheet rock. Again, after sacrificing few bolts, I had my own custom toggle bolt. It worked - I was able to install rest of the hooks this way.

Not sure how much load capacity I compromised cutting the wings off. Hope it doesn't fall on my head. Not an ideal solution - nonetheless, something to think about if your shelf is not going to be holding all volumes of encyclopedia britannica.

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You can cut a slot in the drywall so that the wings don't have to fold. Select or cut a screw to the proper length.

WARNING: This will not be as strong as the traditional installation method.

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