Building a corner shelf into a tile shower doesn't have to be complicated or expensive. The easiest and most durable way to install one is to add it while tiling the rest of the wall. This incorporates the shelf into the wall, giving it a firm support system that is waterproof and permanent. You can use the standard tools required to build the rest of your tile shower wall and a pre-cut corner half-tile shelf.
Install the wall tile up to the height for your shelf. The first shelf should sit on top of the last row of tiles around the height of your waist.
Mix the thinset mortar according to the manufacturer's direction.
Apply a thin layer of thinset mortar to the backer board in the corner with the trowel. The shelf will sit on the last row of tiles in the corner of your shower. Place the half-tile corner shelf on the last row of tiles in the corner with the finished side facing up. Apply more thinset mortar under the tile for extra hold and tap the tile firmly back into the corner so that it is even and perpendicular to the wall's tiles.
Tile the rest of the shower until the tiles reach the corner. Lay the last full tile before the corner and the new shelf. To determine the shape of the tile sitting on top of the new shelf, lay the corner wall tile over the shelf and mark the bottom area to be cut out with a pencil and straight edge.
Lay the wall tile on the electric tile cutter. Hold the tile firmly and pass it carefully into the blade of the cutter. Make the short up-cut before finishing the wall tile with the longer cut.
Apply thinset mortar to that backer board above the shelf and lay the custom-cut tiles into the corner. The fit should be tight with just enough space to force a thin bead of grout into the space between the shelf and the wall tiles.
Grout the area around the corner shelf. Finish tiling the remaining shower walls. When applying grout in between the shower's tiles, fill in all gaps around the shelf with the trowel, pushing the grout tightly into the spaces between the shelf and the wall tiles. Wipe away excess grout with warm water and a sponge while the grout is still damp
Pick a tile shelf that matches or complements the surrounding tile. A tile corner shelf up to 12 inches wide performs best for this type of installation.
Wear safety glasses when cutting tile. Be careful when using the electric tile cutter. Use a push stick to keep the tile close to the platform to keep your fingers away from the blade.