I’m trying to hang shelves but the wall that I am hanging them on is technically an exterior wall.

I live in a Florida home build in 1981. I’m assuming that they used concrete block filled in with cement about 3/4 of the way up the house and then line the inside of the wall with drywall then painted.

I tried to pre-drill a hole with my Kobalt 24V Hammer Drill with a Tapcon 5/32 drill bit. The bit goes through the drywall and hit the concrete but will NOT go any further. I have the drill in hammer mode, on the 2-speed gear option and on the 24 “position clutch”. (Basically the same as a video I watched showing how to use this drill). But nothing is going through.

  • 3
    I would try to move the drill hole about a half inch. Possible you found a nail/screw head or a hard stone in that place. It should go though a hard stone, but the going is very slow.
    – crip659
    Jul 6, 2023 at 11:54
  • 1
    Don't use 3/16" Tapcons, ever. It's 1/4" all day. Or larger. Been doing this +30y; those don't work for me either. Why can't I drive this Tapcon into concrete?
    – Mazura
    Aug 5, 2023 at 20:16

1 Answer 1


The drywall is not just glued onto the block. It is anchored to firring strips that run vertically at the usual 16" on centers.

In some instances builders had 3/4" polyisocyanurate solid insulation against the block and the firring strips holding the insulation in. Usually anchored with concrete nails driven from a pneumatic gun. That would mean between drywall, firring strips , ( or the 3/4" void between the strips.) and solid insulation you have 2 inches to get to the block. Attaching screws to block and having 1 1/4 to 2 inches of non-load bearing material between the inner wall and the block is not good.

If you want to mount shelves you need to find the firring strips and mount the shelve brackets to those. If the shelves are to hold very heavy items you need to drill into the block. Otherwise screws into the firring strips will hold most normal household things. If you have just a small load you can use Drywall anchors.

As for the drill not going through the block, be sure the drill is in the forward position, or get a new bit.

  • How do I find the firring strips? Are these “studs”? The shelves will be used as cat shelves. So less than 20lbs at a time on each shelf (depending on if a cat is on the shelf).
    – Wolfah
    Jul 5, 2023 at 22:47
  • Sorry meant to also add that the drill bit is new today, just opened it, and yes the drill was 100% in forward mode.
    – Wolfah
    Jul 5, 2023 at 23:03
  • 2
    @Wolfah Firing strips are pieces of wood. Can be as small as 1x2s to 2x6s, but usually not used as structural members, more like spacers/fillers.
    – crip659
    Jul 5, 2023 at 23:04
  • At less than 20 lbs, don't worry about getting anything into block. Try to hit the firring strips or get drywall anchors . I edited my answer to show an example of the anchors.
    – RMDman
    Jul 5, 2023 at 23:25
  • 1
    In my area of Florida, ( mid-west) it was required to have battens or firring strips between the block and drywall.
    – RMDman
    Aug 5, 2023 at 13:40

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