Installation of interior window sills

We will soon be installing the window sills (inside). The plan is to install oiled window sills made of solid wood.

I would like to fix the sills with mounting foam. The questions that now arise are:

[*]Should I use a 1K or 2K foam?
[*]And is there a problem with the oiled sills? How is the adhesion of the foam on the oiled sills?
[*]Or is oiling on the underside even necessary to make the sills more durable, or can I skip that?

You want open-pored window sills? But you are also aware that they are very sensitive?

You want open-pored window sills? But you are also aware that they are very sensitive?

Yes, I am aware of that. But since probably not much will be placed on the window sills...

The alternative would be to treat them with hard wax, but we do not want to paint them.

How does it behave with hard wax in terms of foam? Do I have to remove the wax layer beforehand and how?

From the gut feeling, I wouldn't oil or wax the bottom side. But probably knows better

Take a 2K foam, which does not deform as much and hardens faster. However, still make sure to secure the benches. This guarantees that they stay level. If you want to oil, I recommend a parquet oil that is more resistant to moisture. Oiling the bottom is not necessary since they are fixed. Oil the front side and a few centimeters of the underside (as much as they protrude) beforehand as well.

Thanks for the tip. Do I understand correctly that moisture from below the masonry is not a problem? My assumption was that the new building still releases quite a bit of moisture at the beginning. If the boards are not painted on the underside, is there not a risk that they will warp?

For the parquet oil, presumably one with wax content?