I don't know how it's outside of Germany, but at least in Germany in every public sauna there are signs saying "No sweat on wood!" (or in German: "Kein Schweiß aufs Holz!")

What this should mean is that too keep the wood from getting too much salt exposure, you should always sit or lay on a big towel which prevents your body from touching the wood.

Of course the experience is extremely sweaty, thats the reason to go there, so you're correct on that part :)

It is. That's why you should sit on a towel, instead of directly on the bench, with your nekkid sweaty butt.