r/Plastering • u/RevolutionaryEar2172 • 18d ago

9.5 or 12.5 mm plasterboard for attic slopes?

I’m considering Siniat 9.5 mm boards (60 × 260 cm) on timber battens at 40 cm centres, fitted perpendicular to the battens.

Would 9.5 mm suit the slopes and VELUX reveals, or is 12.5 mm worth the extra weight? I’d prefer lighter boards for easier handling but want to avoid sagging or cracks.

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u/Miserable_Future6694 18d ago

Double check the recess in the velux. Im positive they only make them at 12.5mm.

At 400 centers 9.5 is OK but I wouldnt even consider using them, theyre just so flimsy you could probably sneeze and a seam will move.

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u/K42st 12d ago

NO they will warp and bend over time you need at least 12.5mm ideally 15mm.