In article ,
Ian Clowes writes:
Hi all

I'm tiling the kitchen, and am pondering how to best prep the window
sill.

After removing the current window board I'l looking at the top of the
inner leaf of bricks, and the plastic cavity filler. I'm wondering
about the best way to level this, make it a sturdy suface for tiling
onto, and possibly including some insulation to prevent an overly cold
feel or a cause of constant condensation.

I put a sand and cement bed on the top of the bricks, leveled
and smoothed off. Later (about 3 years later in my case), I
got round to tiling it. You can actually lay the tiles directly
in the sand and cement, although they bond better if you do it
separately afterwards with tile adhesive and it's easier to get
a good level finish if you're not familiar with using mortar
and laying bricks level.

--
Andrew Gabriel