Do any concrete screws exist that don't require pre-drilling?

[Greenalleycat]

This started as me wanting to do some DIY at home but also has some benefit to engineering

Obviously, plenty of screws exist that self-tap into timber and don't require pre-drilling
Equally, screws now exist with winged heads that allow for self-tapping into steel
But does anything exist that can accomplish the same thing in concrete or masonry? Everything that I can find requires pre-drilling to the shank diameter
If not, why not? Is it because of the composite variable nature of a concrete matrix?

 

[Tomfh]

I’ve wondered this too. I don’t think they exist.

Concrete, like steel, is too hard to screw straight into. The material won’t yield and displace laterally to allow the fastener to penetrate. So you need to drill a hole. For steel self drillers it’s simple, you attach a short drill bit longer than the material thickness to the head of the screw, i.e. a metal screw. Now imagine an analogous fastener for concrete. How long would the drill bit on the end of the screw section need to be? Would people be happy with 200mm pilot bits hanging out the other side of their wall or slab?

Happy to be proven wrong if it means I get concrete self drilling screw.

 

[hokie66]

Yes, depth into the concrete is a big issue. With steel, the self tappers only work to limited thickness. Attaching sacrificial masonry bits to the end of screws would just be too expensive.

 

[Greenalleycat]

Masonry bits aren't sacrificial though, when you use a hammer or SDS drill you can get a fair few holes out of one before it gives up
I would imagine it would be possible to put one on the end of a screw and have wider threads to cut outside the line of the masonry bit

I can understand this potentially being expensive but there would be a time saving aspect too
Instead of putting up a piece of timber, pre-drilling timber + concrete with an SDS drill, then installing a bolt with an impact wrench, you could just use one tool (hammer drill? impact wrench?) and put a fixing in
Would prevent stuff moving etc and difficulties of realigning timber that has shifted between hole drills too

I am sure fixing companies have considered this so there must be some limitation I don't understand, but would be curious to know if anyone has any knowledge
Perhaps getting the concrete dust out of the hole is the hardest part

 

[human909]

Perhaps getting the concrete dust out of the hole is the hardest part

Bingo.

Oh and think about the 'hammer' part in your first comment. How do you have a hammering action when you are trying to cut threads and drill a screw. These are contradictory requirments.

To hole a material you need to break, abrade, shear and remove the material or displace it laterally. Displacing the material laterally is a non starter in concrete, its difficult and if you did manage to achieve it you would likely initiate a crack.

 

[Tomfh]

Masonry bits aren't sacrificial though, when you use a hammer or SDS drill you can get a fair few holes out of one before it gives up

"Sacrificial" as in it gets left in-situ. It doesn't mean it's worn out. Likewise metal screws can be used many times before the cutting head fails. Notheless they are sacrificed and left hanging out the other side.

Bingo.

It's not that. It's that the screwing stage advances far quicker than the drilling stage, and thus the drilling needs to be complete before the screw thread begins to engage, otherwise you get incompatible progression of the drill and screw, resulting in lock up or thread stripping. For concrete you'd need a very very long sacrificial masonry head, which would be left hanging out the other side.

 

[JLNJ]

Try powder-actuated fasteners. Not really accessible for the DIY home owner, but they don't require pre-drilling.

 

[bugbus]

Concrete nails? Doesn't require pre-drilling.

 

[BridgeSmith]

Try powder-actuated fasteners. Not really accessible for the DIY home owner, but they don't require pre-drilling.

They're accessible to anyone who wants to walk into a big box store or a hardware store and buy them. They are also readily available online.

Rod Smith, P.E., The artist formerly known as HotRod10