Wright length of drywall screws

[svouts]

I am installing a new ceiling with resilient bars and 15mm acoustic plasterboard. I have two boxes of 3.5 x 25mm and 3.5 x 32mm drywall screws.
Can I use the 32mm to attach the resilient bars to the joists and the 25mm to attach the plasterboard to the bars, or they are two short?

PS: between the resilient bars and the joists I will install a 3mm soundproof barrier mat which is 5kg/m2

 

[pinenot]

You'll want self drilling screws otherwise the push required to get ordinary bugle head P/B screws started can be something of a disaster, in my experience...pinenot

 

[svouts]

Do I need self drilling screws both for attaching the resilient bars to the joists and also for attaching the plasterboard to the bars?

 

[pinenot]

No just for screwing the plasterboard to the resilient bars, most resilient bars have holes already in the joist flange and where there's not one you can simply punch a hole through with a nail punch.
Its only the free side that moves too easily when trying to screwing into it, but I've seen some of the professional guys using small "C" vice clamps to lock the metal bar flange to the plasterboard back at the exposed edge. Once screwed of course all fine but the ones in the middle of the sheets are the problem...pinenot

 

[pred]

My favorite trick is to use battons 2"X1" and screw these to the joist with Spax screws 100mm long every 16" or so, what is the existing ceiling PB or lathe and plaster?

 

[svouts]

I have removed the ceiling to installing mineral wool between the joists. Then I will install Tecsound50 acoustic mat, I will staple it to the joists. Then I am installing the resilient bars and the plasterboard. For the plasterboard to the resilient bars I cannot use longer than 25mm screws since longer will penetrate the acoustic mat, I will order self drilling. Now the 32mm screws for the resilient bars to the joists are OK or will need longer?

 

[hammerswinger]

I would say that the 25mm screws to fix the resilient bars to the joists would be fine, the thickness of the flange on the bars is only a millimeter if that so you have almost all of the screw in the joist.

The plaster board to resilient bars screws only need to be the thickness of the plasterboard you are using + a bit to go into the bars, once again I would say 25mm would be fine as any more than the thickness of the bars will just be sticking up in the air!


Cheers.