Any thoughts?

I have a gable end on a tiled cottage, with blown render.

http://www.mauve.plus.com/roof1.jpg

I'm considering instead of the traditional several-yearly render-swear as
it's fallen off in freeze/thaw cycles, repeat, doing it once.

Basically the idea is:
Obtain flamed granite tiles (the sort with a matt face) - looking like 150
quidish + shipping for both gables.

Render to a nice square surface, using battens, ...
Apply small stainless bolts to the backside of the granite using epoxy
(have the bolts and the epoxy), then drill appropriate holes in the gable end.
Apply 'swimming pool' tile adhesive, and locate the bolts/holes so they don't
fall off while the tile adhesive goes off.

Grout with ???

Basically, I'm aiming at something subdued gray, with a little patterning,
to somewhat match the harling, not actually any of the more
exotic colours.

The flashing to the tiles would also be changed - a granite trim down the side, and a small bit of lead.