Levelling mosaic tiles on wonkey window ledge

[Curlywurly]

Hello tiling professionals.

I have no tiling experience and have come across a problem that I would really appreciate some help with.

I am a decorating novice using my downstairs loo as a practice before attempting other projects in my new build house.

I would like to tile a splashback for the sink and also the recessed window ledge. I have noticd that the window ledge is not level. It falls away/slopes towards the window frame by 0.5cm. I would like to use mosaic tiles and feel that this slope would be more obvious when tiled so my question is; what would be the best way to build up the ledge close to the window frame, getting thinner and thinner toward the inner edge? Filler? Plaster?

Thank you in advance.....

 

[White Room]

You could put a batten and fix with screws or nails to the front of the cill and level then build up with a gypsum plaster....thistle bonding preferably.

 

[beanz]

Is there enough space on the window frame, to allow building the cill up? Might seem like a stupid question, but sometimes they're tight, and could be why you have a sloping cill now..

 

[Time's Ran Out]

Using a 1 inch strip of tile or the mosaic, fix these at the window frame side of the window ledge to gain the 4-6mm height to build up the back of the cill. Using a cement based mosaic fix tile adhesive and the flat edge of a 4mm serrated trowel 'level' it out front to new height back. Allow to set then fix away!