ᐅ Which basecoat board should be used when insulation is not a factor?

For aesthetic reasons and weather protection, I want to plaster a shed made of OSB boards in the color of the house. Since it is just a shed, insulation does not matter at all, but apparently you cannot plaster directly onto OSB, so a plaster base board is required underneath.

Can I simply attach 2cm (0.8 inch) polystyrene panels from the hardware store, or does it have to be something special? At the hardware store with the two “o”s in the middle, for example, the following options are available:

• sw*sspor multipurpose insulation board EPS DEO 100 x 50 x 2 cm (39 x 20 x 0.8 inches), €1.10
• sw*sspor multipurpose insulation board EPS WI/DI 100 x 50 x 2 cm (39 x 20 x 0.8 inches), €0.90

Since I have no experience at all:

• What is the difference between DEO, WI/DI, ... and what thickness should I choose?
• Should I fix it with polystyrene adhesive, or screw it on, or ...?

HWL board fastened with insulation anchors

That looks good but is naturally quite a bit more expensive. What thickness would I need in that case—would the thin 8mm (0.3 inch) panels be sufficient?
Since the base is wood, I would probably need insulation screws instead of insulation anchors.

Would it possibly make sense, or even be feasible, to build the shed directly from (thicker) wood wool panels and leave out the OSB?
The downside would probably be that the panel is not as stable and you wouldn’t be able to attach heavy items to it...

The 8mm plates are completely sufficient. Mesh reinforcement needs to be applied over the entire surface in the plaster anyway. You are right about using insulation anchors / insulation washers. The plug should not be used here.

HWL boards are not suitable as a load-bearing layer of a wall, as they are not stable enough.

Thank you for the response! That already helps me a lot.
Since it’s still a somewhat price-related question (I would need 45m2 (484ft2)), what speaks against the above-mentioned expanded polystyrene boards and explicitly for the wood wool cement boards? The final price for the quantity would be about €400 versus €100.

... in case anyone is still interested, I ended up using 3cm (1¼ inches) styrofoam boards, and for the base, 2cm (¾ inch) perimeter insulation boards. They were glued on with cartridge foam adhesive. The plastering went smoothly without major issues, and it looks fantastic, like a solid construction. The summer temperatures have been successfully endured, and now I am curious to see how it holds up during the winter.