Thinnest wall boards/panels/sheets for stud walls of indoor sauna

MichaelR

Hello,

I am planning the building of an indoor sauna. It is to be built on 2 inch studding with Rockwool insulation. The internal sauna wall boards are being bought from a specialized company. But two of the sauna's four walls will be facing the inside of the bathroom and need some material on the external, non-hot, side of the studs.

The finish is likely to be PVC tongue-and-groove panels, already in use in this bathroom. But one needs some material to back them.

The standard would probably be moisture-resistant plasterboard. But it is all of 12 mm thick, it is a bit muich, especially since I need 4-5 mm more for the PVC boards - this makes a bit much. Is there any reliable hard backing material that I could use in 9 mm or ideally 6 mm? It won't be load hearing, hooks (if any) can go into the studs, but of one occasionally leans on it, it should not just break. And it must resist moisture, though won't be directly drenched in water.

Marine ply starts at 12 mm, so appears useless. There is MR ply in 6/9 mm but I guess it might bend despite the MR grade?

One more option I could think of is acrylic sheeting - would that work?

Lumen

9mm multi pro

MichaelR

As in 9mm magnesium board? Thanks will look!

Also I found cement-coated backer boards like Baseboard which start at 6 mm, would these be suitable for installing on studs without any further backing?

(Ideally I'd want a material that comes in 1200x600 or 1200x800 boards, not 2400x1200 - the project is small and I'd like to minimize cutting and minimize the need for vans. But this is not an absolute requirement... but Baseboard does seem to have this option)

Lumen

That baseboard looks good but 6mm isn't enough for stud wall, see p8 onwards of the data sheet

https://quantumgroupni.com/app/uploads/2019/11/Baseboard-Tray-Datasheet.pdf

MichaelR

Went to the shops and found two apparently workable thin options: 6 mm magnesium board and 5 mm Perspex.

MichaelR

Took a look at the Baseboard in a shop and I think I'll just put the 6 mm on stud wall.