Installation of interior window sills

Well, if moisture can rise from the masonry, something is wrong, that shouldn't happen.

You can use an oil-wax combination, whatever you prefer. Just pay attention to the application instructions of the respective manufacturer, then you can't go wrong. But keep in mind that the oil also "enhances" the wood, meaning it becomes darker. You can anticipate this effect beforehand by wetting the board first; this color change will be permanent after oiling.

Thank you very much, I will tackle this next week.

Gladly, and pictures with the result would be nice. ;)

Sure, I will add that here then. By the way, the parquet fitter also gave me the tip to oil the boards only after installation. There was also the note that one-sided coating is not a problem.

The tip comes from the idea of not having to pay so much attention to contamination during installation. I usually oil beforehand, after the boards have already been precisely fitted. This makes assembly easier and also quicker.

One more question. If I oil the window sills in advance, could there possibly be an adhesion problem with the acrylic? I would have sprayed the boards all around with acrylic.