Let's look at the joints that do apply in interior applications of all types.
A cold joint is formed when one mortar setting bed has cured and another adjoining mortar bed is placed next to it. The common cold joint locations are found at the place where the mortar and tile backsplash and counter top meet and where the mortar and tile shower floor and wall meet.
Tile Doctor Tip: Wherever tile meets tile in inside corners, treat this intersection as a cold joint. This intersection is subjected to a great deal of movement in the adjoining fields of tile. This is a notorious spot for the failure of hard grout joints. These joints, when not treated properly, will fail and cracking and dislodging of grout is common.
This joint is a perimeter joint. This joint is found where the field of tile meets adjoining walls. This joint is often overlooked, resulting in tile floor failure. This type of joint needs to extend through the tile work. Now let's discuss other expansion joints common to exteriors. These joints can be present in interiors as well, especially in large expanses of tile.
A control joint is an intentionally weakened break in a concrete surface to allow for contraction stress. These joints are most often seen in concrete slabs. The concrete worker will score the concrete at intervals using a control joint cutter or trowel. Often these joints are cut after the concrete is poured, using a concrete saw. The concrete is generally scored only, not cut all the way through. This allows the concrete to naturally crack at a joint and not elsewhere in the slab. Remember that concrete cures by hydration. That means that while the concrete is curing or drying, water is being released. This causes the concrete to shrink. Control joints need only to extend through the tile work.
ISOLATION OR CONSTRUCTION JOINT
This joint is similar to a control joint in that it is designed to allow the concrete to crack at known locations. However, the joint is continuous through the concrete and reinforcing, and is formed at the time the concrete is poured. It is often seen with a felt or similar material visible in the joint. These joints need to extend through the tile work.
This is a planned for and constructed joint. Normally found in the field of larger tiled floors and walls. This joint extends through the tile work, through the substrate, and through the reinforcing wire. Proper expansion joint design and construction are necessary for the success of the joint.