wannabath is correct, acrylic tubs need to be set in a mortar bed for them to not flex and crack, I've seen many installers not use anything to set these tubs. Secondly, an applied epoxy finish is not like the glazing that is done in the factory, but I have had this done on several projects and it turned out very well and stood up to a lot of abuse and still looks great. However, not all tub refinishers are created equal. Its best to look at their products before you hire them and look at the warranty. Another material that is available in some tub configurations is a combination of resin with volcanic rock. It hold the heat better than acrylic, doesn't scratch like acrylic, but is lighter than cast iron. On new construction I still use cast iron for secondary baths, but use the volcanic rock tubs in master baths. Victoria and Albert make these tubs.
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Proper way of installing acrylic bathtub
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