Mold and new shower liners?

Question:When those comapnies come and install a new shower liner over your old shower...what happens to the mold and mildew on your old tile and tub? The grout? Does it continue to spread? what happens to it?

Is it really that easy? ust cover it up?

Answers:
They chemically treat the surface before they install the liner. Any soap scum or mildew would prevent adhesion.