ᐅ Which filling and adhesive materials are recommended for interior window sills made of stone or marble?

Hello everyone,

Please see the attachment. Our new windows partially have two window sill strips at the bottom, each about 3cm (1 inch) thick. What material would you use to fill the area underneath? What would be suitable here?

Has anyone had any tips or similar filling techniques?

I had an average gap of 4.5 cm (1.8 inches). I filled it once with some leftover tile adhesive applied in small blobs. Just that thickness, and then I placed the windowsill on top. The rest I filled with foam and then plastered over it.

For the other windows, I did the same using Perlisan insulating plaster, but since it didn’t adhere very well, I distributed some plastic mounting blocks. For one windowsill, I had nearly 6 cm (2.4 inches) and applied the layers step by step.

So far, everything seems to be holding up well...

Great, thanks. A few drops and leftover foam sounds interesting. I might have been overcomplicating it and was thinking about creating a formwork and pouring something in before gluing the rest.

Yes, I had the same issue at the beginning. I would like to point out that you have a much greater height difference. That definitely makes a difference. How much support area does the bench have?

If you use marble or other natural stone, please do not use regular tile adhesive, but rather natural stone adhesive. Regular adhesive can sometimes cause unsightly stains on the surface.
I also adjusted the height using wooden and plastic wedges along with adhesive.