OK let me add another screw to the mix:
http://www.toolstation.com/shop/Screws+Fixings//Reisser+Cutter+Screw+40+x+25mm/d/sd/p95628
£3.50 for 200 screws. They go in a dream with an impact driver (a must for Hardie).
IMO drywall screws are too thin to drive through concrete. I would imagine by the time it got through the other side it would look more like a nail!
http://www.toolstation.com/shop/Screws+Fixings//Reisser+Cutter+Screw+40+x+25mm/d/sd/p95628
£3.50 for 200 screws. They go in a dream with an impact driver (a must for Hardie).
IMO drywall screws are too thin to drive through concrete. I would imagine by the time it got through the other side it would look more like a nail!