OSB in the bathroom as flooring, how to seal it?

Good day,

we are currently completely renovating our house from 1955, including the bathroom. Since we can only realize a maximum floor build-up height of 2 cm, we have recessed 22 mm OSB flush between the floor joists. On top of that, 12 mm OSB is to be laid and screwed.

We are now looking for a suitable waterproofing solution for this.

We are aware that OSB in the bathroom, especially on the floor, is anything but optimal, but another construction was not feasible without creating a massive step into the bathroom.

As a covering, we would like to glue vinyl.

Who can help us with tips and tricks? There must definitely be solutions, after all, OSB is the solution for everything in the USA, for example.

Best regards and thank you

We have as well. The tiler then normally sealed with the blue stuff. Absolutely stable for 6 years and it works.

Sealing membrane. As in other bathrooms as well. Sopro, Knauf, Isolbau, etc. It is glued to the floor (as in the shower too). Please do not use liquid sealing compound. And also pull it a few centimeters up over the corners/wall connections.

My brother completely covered the wooden floor with thick bitumen sheets (hot applied) during his last bathroom renovation (and bent up at the edges). "Of course," in addition, the usual sealants were applied over that (under the tiles).