This question discusses vinyl tile flooring underlayment in a bathroom, but fails to address how waterproof the answer can be.
In my project, we have water-damaged bathroom subfloor and have pulled out vinyl flooring that was on top of it and then cut out the subfloor in order to replace it. In our replacement, we're going to use thin vinyl tiles instead of rolled out vinyl flooring. We plan to put down 1/4 inch birch sheets (someone told me it was called "luon") on top the replaced plywood subflooring. Between the luon and the plywood subflooring, I was told to use self-leveling compound. But then we planned to put the vinyl tile squares right on top the luon. My worry there, however, is that even if we place the tiles very close together, water will seep through, hit the luon, and bubble it. So, my question is -- are we supposed to put a material or flooring on top of the luon before we put the thin vinyl tile squares?
I'm wondering if we should be using concrete board instead of luon, and then put the vinyl tile on that, or if we're supposed to smear some compound on the luon to waterproof it, or some other thing we're supposed to do so that water that leaks to the luon won't cause it to bubble.