The joint between the pool coping and patio is an area that should be sealed to prevent water from weeping in and affecting your swimming pool. Many people mistakenly believe the joint is simply cosmetic. It is also functional and allows movement between the patio and the structure of the pool.
The photo below illustrates the expansion line between this bluestone coping and the pool patio on this steel walled vinyl liner pool.
The photo below is the same pool, with the expansion joint filled in with SikaFlex Self-levelling caulk in tan.
In the photo above the expansion line was left empty and became a place for debris and other materials to get trapped, as well as for water to leak in between the coping and patio, causing tile issues and pop-off.
Here is an example of the tile area affected. Water and moisture behind the tile will wick down into the gunite, and when it freezes/thaws the expansion and contraction can cause tile to pop.
Here is an example of the tile area affected. Water and moisture behind the tile will wick down into the gunite, and when it freezes/thaws the expansion and contraction can cause tile to pop.Here is the pool with the new tile, and cleaned out and freshly caulked expansion joint.
Home Depot carries what we commonly use, learn more here: