Screw floor plaster?

[mhacker]

Currently screwing down floor gypsum at home and wondering why the screws need to be so close together? Most recommend placing them 15-30 cm apart, but that ends up being around 40 screws on a 60x240 cm sheet, is that really right?

Another question concerns the screws themselves and the screwing technique. I bought Grabber self-drilling screws. These are threaded "the wrong way" the last few millimeters before the screw head. What is the purpose of this, should I use a special technique to drive the screws in? As it is now, I let the screw drill into the sheet with the drill tip and then follow up with the screwdriver once it catches. You have to apply quite a bit of force to prevent the bit from jumping out, is that normal?

 

[Farzan]

You have to use a fair amount of force to keep the bits from jumping out, is that normal?

Yes, I've only screwed floor gips once (one room) and that's exactly how I experienced it. Floor gips is very hard so it takes a bit of force to get the screw in.

Now, I initially had (eh, I blame the guy in the store..?) the wrong screw, namely one intended for "robust gips." It was tough to screw and many broke right under the head when trying to get them in. With screws intended for floor gips, it was somewhat easier. But that seems to be what you have.