how would you attach this decorative board?

[Yrrol]

It might be 150cm one way and 30cm the other way, shaped like an L

Would you just glue it to the waterproofing membrane, or also screw?

 

[KnockOnWood]

I would absolutely try with sättlim or NoMoreNails.

If it's not sufficient, you can supplement with screws later.

But what is it? Tätskikt = bathroom???

 

[SuperBengt]

Some form of glue, personally I would go with esstack. It adheres to most surfaces, holds good weights. Like many other glues, admittedly, but from personal experience, it's the best glue option.

http://esstack.com/sv/index.html - pro1 is what I have in mind

 

[Yrrol]

Preferably don't want the glue to become too elastic, is pro1 more rigid?

 

[MathiasS]

Sika might be easier to obtain and they have many suitable products. If you want something that grips a bit, then perhaps Sika Maxtack could be an option. Otherwise, there are several construction adhesives in the Sikabond series that work.

 

[Yrrol]

I have esstack xtreme at home, it is apparently less elastic than pro1 according to their page. However, I find it has been difficult to work with, and if you happen to spill, you can't remove the spill. - but maybe that's the case with all adhesives.

 

[Yrrol]

Drove esstack xtrem = insanely thick string that didn't spread out. In other words, the board ended up far from the box.

Now considering removing the board and cleaning off the dried glue residues to make a new attempt, probably with the lighter pro1.

Is it possible to cut it loose with fishing line, I wonder? I don't want to damage the surface that should be outward.
Once it's loose, I'm thinking about using a scraper disc on the multitool.