Marmox boards - screws

[DDD]

Hi everyone, new here (I will introduce myself, but really need an answer so I can order the stuff I need).

Ok, so I have stud and block walls, suspended timber floor (WBP). I'm putting marmox boards on both walls and floor. Floor will have a Devi-mat. Using Mapei Keraquick to attach boards to floor and block walls, then screwing and just screwing onto the stud. Will be getting Marmox metal washers (I assume there's no problem using these with the UFH). Now.. everywhere I read says use apropriate stainless steel screws. Please could someone enlighten me on what size these are? Using 12.5mm boards, so thinking at least 30mm long, maybe longer but what diameter?

thanks

D

 

[cam_low]

You just have to think about entering the wpb far enough (3/4) to get a good hold. You don't want 50mm screws with having the chance of bursting pipes below the wpb. As for diameter I think I use around 4mm iirc

 

[DDD]

Thanks, I as looking at 4mm and 4.5mm screws, so great to finally hear what someone else is using.
No chance of burst pipes as there is a 3 foot space under floor and can check where all the plumbing is, but don't really want lots of screws poking through, so 12.5mm marmox + 18mm wbp +3mm adhesive = 33.5mm. 3/4 through wbp = 13.5mm, which would seem to imply 29mm minimum length I've found 25mm or 32mm screws. Was thinking maybe the 25mm, but looking at the figures the 32mm might be better. For the block wall and stud, should I go longer.

I think I've everything else covered; just deciding whether to tank on top of the SLC (covering the UFH), or if taping/sealing the edges the marmox boards is sufficient.

D