ᐅ Sealing natural stone windowsills on the interior side?

Hello everyone,

I am new here and hope to get an answer to my question, preferably with an explanation.

Tomorrow we will be installing the interior window sills made of natural stone (Steel Grey). The slabs are 2cm (0.8 inches) thick and will be fixed with cement mortar. My question is: does the window sill need to be sealed with a sealing tape? I have heard something about that, but it doesn’t seem very plausible to me.

Best regards, Micha

Where is that supposed to go? Our ground floor has a silicone joint at the window, discreetly done with clear silicone. The wall connections are sealed with acrylic. The area below is skim-coated. I don't see any need for a sealing tape there.

No, of course not. They are usually just set into the mortar bed.

Thank you for your replies, we omitted the waterproofing.