Painting exterior windows

Hi,

I have had my kitchen window changed for a PVC one, and they had to raise the level of the window sill.
So now I have a section of wall that is (I presume) rough sand and cement, which needs to be painted.

I have primed it with stabilising solution, but I don't know how to make it a smooth surface? Is there an exterior plaster like substance I can use to make it smooth before painting?

Also I started stripping back the original window sill, I'm not sure if its stone or concrete, and large sections of the top have come off (I think due to previous water damage from leaking guttering)
The bits coming off seem to be a layer of plaster like stuff with a different type on top.

Again I don't know if I can just paint strait onto the original window sill or if i need to put a protective lay on first to make is smooth?

Any advice very welcome!

The lump you are holding is probably filler of some kind + whatever on top of it. To fill cracks on the sill and to make the other surface smooth use an exterior filler perhaps MurEx here http://www.toupret.co.uk/business-customers/products/exterior-fillers.html is your best bet.

To make the sill smoth, sand it first (as you should gently sand the rough sand and cement area). If the sill has imperfection (hollows) you willl have to fill them using the filler as above.