Window sill removal and tiling

[xAlex]

Hi all,
I want to remove the window sill so that I can tile as I understand it’s not a good idea to tile on to MDF, and in any case the edge of the sill overlaps the wall. It is a new-build timber frame house.
Q1: what can I expect to find under the sill?
Q2 what do I replace the sill with to make a suitable base for the tiles?

Thank you

 

[foxhole]

You can cut the overhang off and tile onto.

 

[Keithmac]

I did that in our WC and it worked out well, was wood but not MDF mind.