A foam strip may be installed on a pool that is brand new. It separates the deck from the coping stones. This is your "perimeter extension" joint. These are the lateral expansion joints. To allow concrete slabs to expand in warm weather without pushing against the pool wall or pool coping, expansion joints are installed between the pool deck, the patio and the home.
Caulking is not necessary for all pools. Only in-ground pools with concrete decks or coping stones require swim spa caulking. Ice is one of the most powerful forces in nature. Water expands with tremendous force when it freezes. Ice can fracture steel, concrete, and rock, as well as any other material that is in its path. Concrete expands in warm weather.
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The pool wall is always defeated by the horizontal pool deck in a battle between the vertical pool wall, and both are expanding. This prevents the expansion joint's filling with dirt, grit, and other material that can reduce expansion space. If this occurs during warm weather, the expanding deck of the pool will bump into the pool and crack the pool wall.
This prevents water from leaking into the joint during winter. This can cause tile and coping stones to become looser over time or slowly over years. New caulking is great for protecting your pool wall, tile, and coping against cracking and falling apart.