Tiling around window

[average]

S and C render will slow the job down allowing for drying

I agree however one can use an accelerator and leave the reveals to the last and itll be fine. He could even bond it mixed with few handfulls of cement

 

[Dumbo]

Backer are available to some description in most towns . Builders merchants carry them Wickes topps magnets the list goes on . Failing that plaster board . These are the easiest opens .

 

[Dan]

Plasterboard and plasterboard adhesive. Or double tile with off cuts and cement based adhesive...?

 

[defender6]

Rapid set adhesive

 

[SJPurdy]

If you can get it one of the insulating tile backer boards (Wedi, Marmox etc.) would be my preference so that you do not get cold spots on the tiling causing condensation.
Check the set out of the tiling before fixing the sill because sometimes you may be able to adjust the sill height to match perfectly to a horizontal tiling joint.

 

[Dumbo]

Rapid set adhesive

Mind you dry wall adhesive goes of quite quickly