I put a wall mounter server rack directly on my basement wall (hollow cinder blocks). This is an interior wall, e.g. second basement on other side, no dirt.

I mounted it using 1/4" x 3" tapcon screws.

I screwed up, not sure what I was thinking, but 3 of the 4 tapcons went into the hollow part of their blocks (each on a different block). I think my brain decided that the blocks were solid on the top and bottom, just hollow in the middle.

I felt a little unsafe about this, and took everything down.

Now I want to put it all back up using toggle bolts (the "TOGGLER" brand heavy duty 1/4" ones which advertise a great deal of strength in "concrete blocks" pdf warning).

I do not want to / in most parts think that I cannot re-use the holes that I drilled. In the attached photo, the red arrows point to the holes that I drilled. The black keyhole sharpie marks are the proposed drill sites for the toggle bolts.

That's a long winded way of saying: have I weakened the blocks too much to safely use the toggle bolts with these small holes? As a followup, are any of the small holes too close to the proposed toggle bolt sites, and if so, can I do anything about them?

existing holes vs proposed new holes

(I am not actually sure what kind of blocks these year. The TOGGLER documentation lists a strength for "concrete blocks", which I thought means a solid block - and I don't see how you're going to use a toggle bolt in a solid block.)

For reference, the rack itself weighs 80 lbs and can support 200 lbs of equipment. Yeah, I'm probably really overdoing it - but that 200 lbs of equipment represents many thousands of dollars that I do not want to come crashing to the floor.

wider angle view

  • 1
    If you are not worried that you have a much larger hole in one of the blocks for the electrical outlet - I don't think you should worry about your tiny holes. :)
    – EᑎOT
    Commented Oct 6, 2022 at 22:39

1 Answer 1


A few small holes won't weaken a block. A line of ten or twenty holes will.

Off hand would say you have concrete blocks and they should have two large openings, one on each side of the centre(four walls with a centre ~1 inch thick walls).

Cinder blocks usually have a rougher surface, a bit smaller, and much lighter(maybe weaker).

  • Thanks. Based on the few that were left over when I bought the house, I think they are probably concrete just based on weight. They are terrifically heavy compared to the cinder blocks I am used to. Assuming of course that's what those leftover blocks came from.
    – negacao
    Commented Oct 6, 2022 at 19:16
  • Your blocks look smooth, like a cement floor. Cinder blocks, the ones I had, were more of a pock mark surface.
    – crip659
    Commented Oct 6, 2022 at 19:20
  • Ah ha! Thanks, that's a dead giveaway.
    – negacao
    Commented Oct 6, 2022 at 19:25
  • huh... learn something new every day! Didn't realize there was a distinct difference between "cinder blocks" and "concrete blocks". Thanks for the lesson!
    – FreeMan
    Commented Oct 7, 2022 at 15:25

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