This service is called for when caulk is mildewed, cracked or missing. You may also need to consider
re-caulking
when hairline cracks appear in wall joints where grout wasn’t properly caulked.
Caulk is a non-structural, physical compound that provides an airtight, watertight, or non-porous seal. The seal or closure made by caulk is used to prevent something, such as air, water, gas, liquid, or steam, from entering or escaping between two other materials.
Caulk is used to seal joints or spaces between those two materials whether they are similar in substance or not.