The regular house is divided into different sections. Popular practice dictates using different tile styles and colors for every section. The purpose of this practice is to minimize the monotony brought about by using same tile styles in every room. The tiles you put in transition, at the end of a section and the beginning of a new section, is called the tile threshold.
Tile threshold are commonly installed in doorways. Doorways are logical spots to put transitions because afterall, it is the doorways where we enter different sections of the house.
Doorways provide one of the most common transition points for flooring materials, including tile. Not all tile patterns carry through from room to room, and one of the ways you can separate two floors made from different tile is via a threshold in a doorway. The threshold can be made from a variety of materials.
Tile Threshold
The simplest way to install a threshold is to use field tile from one floor or the other, or even an entirely new type of tile. You can cut the pieces down into strips that are as wide as you want the threshold to be and then install them in a bed of thinset mortar applied with a notched trowel. The goal is for the transition pieces to span the gap between materials and be flush with each floor. You still need to allow for joints between any threshold pieces and either tile floor, but you caulk these rather than grout them to allow for movement. You can also use natural stone tiles in a similar fashion, cut into strips or triangles.
Deco Strip Threshold
The same deco strips and border patterns that are sold at home improvement stores to separate different tile on wall areas can also be used in threshold settings. They are installed in mortar just like tile, and while you can grout the joints in between the pieces within the strips since they are glued to plastic mesh, you still need to caulk the joints between the tile floors and the transition strip. Strips are sold in a variety of widths and patterns featuring tiles and natural stones. Common sizes include 3-by-12-inch or 6-by-12-inch.
Marble Threshold
Marble thresholds are available at any home improvement store, and they are specifically designed to be used with tile installations. Typically 2 or 3 inches wide and half an inch thick, they are sold in lengths to fit most common doorways. If you need to trim off an inch or so to fit a custom doorway, you can cut them in a tile wet saw just like a piece of tile. They install the same way in a bed of thinset mortar to flush out or even rise slightly above the face of the surrounding field tiles on each side of the doorway, with a chamfered edge ramping up to the top, flat part of the threshold.
Pebble Threshold
You can buy pebbles in sheets, similar to deco strips, but you can also gather your own river rocks and pebbles and install them on your own in a bed of mortar between two floors at the doorway transition to create your own custom threshold. You can fill the gap between the two areas with mortar and then press the pebbles into place across the threshold width. Then clean the face of the pebbles of excess mortar and allow it to cure.
Threshold Plates
Threshold plates also make a pleasing transition between two different tile floors, and they come in a wide variety of styles. There are simple, single-threshold plates that screw into the subfloor, but you can also find specialty thresholds that have interlocking parts that allow for movement due to foot traffic, along with built-in expansion joints so that the threshold can move independently from either floor.