Trim tiles finish off a tiled surface's exposed edges, giving the job a professional look. Borders act like a picture frame to define space and separate one section of tiles from another.

The most common trim tiles are bullnose pieces, which have one edge that curves into the wall. A "surface bullnose" tile is like a regular flat tile with one edge rounded over.

A "radius bullnose" tile has a more radical curve, so that the body of the tile must rest on a surface—usually, a piece of backerboard or a mortar bed—that is raised above the surrounding surface.

An outside corner requires a special corner tile, with a bullnose edge on two sides. Bullnose tiles may be the same size as the field tiles, or they may be narrower and longer—typically, 2 inches by 6 inches.

Countertops have special trim tile requirements, to cover the front edge of the counter as well as the backsplash.

Borders are available both in single tiles and mosaic sheets. A border may be as wide as 4 inches or as narrow as 1/4 inch. Often, a wide border is installed along with thin border pieces directly above and below it.

Some border pieces have finished edges, so they can be used as trim tiles as well. A border may run horizontally only, or it may also extend vertically to complete a picture frame effect.