Screwing hardi backer

[Flintstone]

Left this for a while before replying as thinking about it I had only used the drywalls on ply and on insulation boards but knew I had a bathroom floor to do using hardibacker 6mm - did it today using the drywalls and every screw went in fine with no sheared heads.

I wouldn't use them on any flooring, as said, they snap far too easily.

 

[Two-Trowels]

Yes they do snap, if you hit them with a big hammer 😉

Shear strength isn't great with drywalls (sideways pressure) and most other screws too for that matter, but shear strength isn't much of a consideration on a floor or ceiling as lateral movement sufficient to snap the fixings is practically non existent. They don't seem to have too much trouble holding up ceilings including the heavy weight stuff like fire protection and sound block boards and besides, I doubt you could get the Hardi up very easily once it's been stuck down with rapid set on a suitably primed floor.

The way I see it is there is only the potential for screws snapping if there is LOTS of lateral movement between the original floor and backer boards and that's doubtful when the job is done right.

 

[AndY mac]

Doing the job right starts from using the proper materials for the job in hand. Not only are the drywall screws not spec for the job the are incredibly alkaline sensitive so not only do you have to worry about there strength they have other issues

 

[Flintstone]

Personally I would rather just spend the extra £1 and use the propper screws instead of some brittle cheap ones that are meant for holding up a bit of plasterboard

 

[Kyle Knowles]

I posted a link for collated wood screws there the ones I use

 

[widler]

Doing the job right starts from using the proper materials for the job in hand. Not only are the drywall screws not spec for the job the are incredibly alkaline sensitive so not only do you have to worry about there strength they have other issues

Im curious what issues a alkaline sensitive screw wiuld have , please explain andy

 

[Time's Ran Out]

Me too, me too!

 

[Qwerty]

Galvanization–passivation–synthetic coating
A) Zinc yellow passivated

B) Zinc-plated, transparent passivated (generally termed "bright galvanised, zinc-plated")

1. The application of a zinc layer protects the material of the screw from corrosion and simultaneously gives it a greyish, silver-coloured appearance.

2. The application of a passivation layer to the zinc-plated surface of a screw results (depending on the chemical process used) in a yellowish or transparent coloration of the metal. The passivation of the zinc layer improves the corrosion protection.

3. After the zinc coating and passivating processes, the screws are given a further synthetic coating, which reduces the screwing-in torque required, making the screws easier to use. SPAX with zinc-plated surfaces are for indoor use. They should not be used outdoors or in damp locations.

 

[Qwerty]

This is from SPAX ^^^

 

[AndY mac]

The phosphate coating on drywall screws in my option is not enough for a coating of tile adhesive. Once screwed in and surface scarred they corrode real quick. Only seen proof of this once. Doing a job with my uncle a bathroom floor with a marble tile spots and discoloration on surface. Once we lifted ply had been screwed down with drywall screws rusted out.