I am in the midst of waterproofing the interior side of my basement. I have many leftover form ties that I've cut off flush with the concrete. The ties originally looked like this:

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My waterproofing sealant (Thoroseal) manual recommends I drill into the ties about 1", and fill the hole with some hydraulic cement before continuing with covering the wall with a sealant. In the image below, the dotted circle is kind of where I'd like my hole. You can see the ground down stubs (cut with an angle grinder) from the ties in the middle.

enter image description here

However, I'm not sure how to accomplish this. I tried purchasing a simple carbide-tipped concrete twist bit, but it jumps around when I try to center it on the ties and I can't get it to drill both the concrete and the metal.

Any tips on how I can successfully drill this hole?

  • 2
    cut the rebar square ... use a punch on the center ... start with a 1/8" drill bit ... drill 1" deep ... try 1/4" drill bit next ... work your way up
    – jsotola
    Jul 5, 2020 at 3:00
  • 2
    I have never heard such crazy advice or requirements. Sealing from the inside is not really effective in my experience unless it just for humidity now high water level trying to chase a tie around drilling sounds like a good way to fracture what seal is there. I grind them off if they don’t break flush with a couple of flexes. If there is enough water to cause problems on new construction the foundation drains were not proper or the exterior seal coat.
    – Ed Beal
    Jul 5, 2020 at 3:05

1 Answer 1


The form ties are steel. So, a masonry ("carbide tipped concrete twist bit") drill is exactly the wrong thing to drill them with - that's what you use to make holes in concrete, which is not what you are trying to do (however absurd it may be to try that - I agree that this is a VERY strange and impractical thing to try doing.) That type of bit utterly stinks at drilling steel, the geometry is very different.

You need to remove the steel, not drill a new hole in the concrete - the steel is already making a hole there, you just need to remove it. So use a bit made for drilling steel, carefully centered, starting with a center-punched divot to keep the drill on track, as @jstola suggests. When you get to the point that you have drilled out almost all of the steel, you may consider switching to a masonry bit if you intend to enlarge the hole beyond the size of the form tie.

Personally, I'd return the product and buy one with less insane directions, as this is a lot of work with little prospect of benefit - it smells like "we know our product doesn't work well, but we'll insist that the problem is that you failed to follow our detailed insane directions so it's not our fault when it does not work." Cutting the ties off flush is the only normal treatment of form ties.

  • 1
    I agree that the drilling sounded like too much work, considering the number of ties there were. I ended up using a masonry grinding wheel on my grinder and just "plunged" it into ties and grind out a slot. It was pretty easy and fast, and then I'll just fill the slot with hydraulic cement. I agree that it's a pretty persnickety requirement, but the product has pretty good reviews when applied correctly, so I'll give it a try
    – atanamir
    Jul 5, 2020 at 17:47

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