Is it me or do Tapcons suck?

I was kind of excited about Tapcons, because they let you a smaller hole than with anchors.

I’ve used Tapcons twice. The first time was to attach an outdoor guard rail to the sidewalk concrete. I drilled holes with the Tapcon bit through the rail’s base plate into the concrete, and tried to drive the Tapcons, but they stalled out about halfway through. I chatted with the Tapcon helpline, and it turns out the screws had probably bound up in the steel base plate. The bit is sized specifically to let the screws drive into concrete. In steel, the bit was a bit too small. Okay.

The second time was today, and last week. I was trying to attach a base for a Little Library to concrete (on a 4x4 post, into a plastic post base). The first time I used 3/16" by 2 1/2" Tapcons, reasoning that the pullout loads wouldn’t be big, and a narrower hole would be faster to drill. So I bought an expensive, weird 5/32" bit, the one Tapcon recommends. Well one screw broke off in the hole about halfway down. So the hole is now useless, and I have to reposition the base.

So I tried again, with 1/4" x 1 1/2" Tapcon screws. I figured the fatter screws would resist breaking better, and the shorter screws would reduce the torque on them (because the resistance increases the farther you drive them.) Again, I used a Tapcon drill bit for the holes, but 3/16" this time. Incidentaly, my M12 Fuel hammer drill had no problem drilling the holes.

And lo, my M12 impact driver (not a Fuel) wouldn’t drive the screws all the way in. It petered out about halfway through.

So I think Tapcons are very picky about depth and diameter. and even if you get it right, your typical DIY level tools might not cut it. The screws have to be short enough that your tools can snug them down, but long enough to handle the pull-out forces, and who knows what those are?

I ended up using the smallest Parawedge anchors (with the cone-shaped nut that expands a brass collar in the hole). They required a 1/4" bit (so that was a third carbide bit to purchase) but my M12 Fuel hammer drill again had no problem drilling a 3" hole (I was generous.) I tapped the anchors in with a hammer, tightened them up, and done.

Why did I bother with Tapcons? What did I do wrong?

I had my own saga with Tapcons a while ago and got some good advice when I posted it on Instagram: Login • Instagram

Basically any Tapcon below 3/16" is garbage, drill way deeper than you need to, and clean out the hole really well.

Moreover you shouldn’t be driving them with an impact driver, the instructions say to drive them with a hammer drill.

Some other advice I received:
Use the hex head not the screw head if possible.
Use two different drill bits. One for the actual drilling and another fresh bit to clean out the hole (tapcons are very sensitive to having the correct hole size, a smaller hole and they’ll bind).

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Thanks!

“Any Tapcon below 3/16” is garbage"? Do you mean 3/8" or maybe 5/16"? I don’t think they come any smaller than 3/16". At least I didn’t see any.

“Moreover you shouldn’t be driving them with an impact driver, the instructions say to drive them with a hammer drill.” Aha, that’s true. (And the hammer function should be off, they say, so I don’t know why you couldn’t use an ordinary drill/driver.) But that wouldn’t have let me drive home that screw that bound up. If the screw wasn’t going to go in with an impact driver, it certainly wouldn’t go in with a drill/driver. I was considering renting a burlier impact driver or wrench.

“Use the hex head not the screw head if possible.” Really? I used hex heads every time, but the screw heads I’ve seen take Torx bits, so they should work okay, right?

“Use two different drill bits. One for the actual drilling and another fresh bit to clean out the hole.” That’s an interesting idea!. I wonder if drilling the holes reduced the diameter of the carbide tips a bit, so each hole was narrower than the last. But then, you’d have to designate one bit specifically for cleaning, because you want it to stay at the right diameter.

Thanks again!

oops, I meant 1/4", I was thinking of 3/16" at the time. That still is worded poorly I guess because 3/16" is the only size below 1/4". I upgraded from 3/16" to 1/4" when I was having issues and they are about 4x less likely to break.

The screws I was using had Phillips heads.

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Ah, sure. Well 1/4" screws have about double the steel for the same length, if I used my calculator right.

Their website points out one advantage, which is that the screws don’t exert any outward pressure, so if and when you break a screw, you can just shift over a bit and drill another hole, and the screw won’t break the concrete, as I suppose anchors could.

They are very picky about hole diameter in my experience. If the hole is even a little undersize they are nearly impossible to drive, if the hole is even a little oversize then they don’t hold well. And it can be tricky to drill precise holes in masonry even if you are using Tapcon branded bits. I’ve had the best luck with Bosch bits specifically made for Tapcons.

I do not believe their website claim about them not exerting outward pressure. If there were no outward pressure there would be nothing to grip the threads. I have experienced this in person as well: many years ago I was tasked by my boss to make a display of various masonry anchor products and accidentally split a few blocks and pavers driving tapcons into them. Now it’s entirely possible that they exert less outward pressure than a wedge anchor, redhead, etc, but it’s certainly not zero.

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Thanks MechaMan, that’s good to hear (because that means it isn’t me.) So there are Bosch bits for Tapcons specifically?

Yeah, I know, that outward pressure thing seems wrong to me too. But they cut their own threads. If the hole were precisely sized to fit the screw shank, then the threads would provide all the pull-out resistance and there wouldn’t be (much) outward pressure. But getting that hole the right size seems difficult, for some reason.

Yes, Bosch makes bits for Tapcons specfically. I don’t remember the exact name they give to them but when I’ve bought them at Lowe’s they’re sitting right beside their normal masonry bits and they’re approximately the same price as well. It says Tapcon on the packaging.
I don’t know this for a fact but my guess as to why this happens is because when you drill masonry you don’t always get a hole that’s the precise diameter of the drill. It’s always a little larger because instead of cutting material like a wood or metal drill does a masonry drill abrades it away. Thus the size of the sand particles in the masonry adds a variable that isn’t present in wood or metal: if you drill in masonry made with very fine sand you get a hole nearly the exact same diameter as the drill. The coarser the sand gets the larger the hole ends up being, so drilling a precise diameter hole in masonry is tricky.

How they hold is a bit strange too. They do “cut threads” to a certain degree but it’s nowhere like a wood or sheet metal screw. If you remove a tapcon from a hole you will see the “threads” are very shallow. I think their holding power is sort of a combination of them cutting very shallow “threads” and also simply being wedged in tightly into the hole allowing the crest of the threads of the tapcon to deform a little. If the hole is too small they can’t cut threads. If the hole is too big then the threads are loose and the screw can’t wedge in place either.

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Hilti
Concrete screws are the best…

Tapcons not going to make it…

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The key to successful Tapcon usage is to drill the hole at least one inch deeper than the screw is long, and to blow out the dust/debris from the hole with a quick blast from your air compressor (mostly applies to holes down in a slab, not a wall or ceiling).

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Ah, that makes total sense, about the size of the particles.

I did notice that when I backed a tapcon out, the threads were visibly ground away near the tip. I think that means you can’t reuse a backed out tapcon.

Thanks. I didn’t blow out the holes, but I did drill them over an inch deeper than the screw, and backed the bit out repeatedly to pull out dust. But maybe that wasn’t enough. No way to tell. :-/