Shower niche edging trim?

[BigAl]

I'm about to start tiling a couple of shower niches in my bathroom and i'm wondering about how to install the trim on the external edges. The concern I have is if they're going to be waterproof? I can't see how it's sealed where the tile meats the strip if I just use the adhesive to bed the strip down? Should silicone come into the equation somewhere? Ta.

[Mike]

as you say it's in the shower, the 'wet' area should be tanked prior to tiling. i leave a 1mm gap between the trim and the edge of the tile and force the grout in. there should be no movement in the trim so the grout should be fine. using silicon i.m.o. will undoubtedly be messy

[BigAl]

Thanks. The shower niches and indeed the entire cubicle has been tanked with Mapei WPS. The niches also have rubber Mapei strips in the corners.