Bathtub refinishing also known as bathtub resurfacing, bathtub reglazing or bathtub re-enameling is the process of refreshing the surface of a worn, damaged bathtub to a like-new condition. This process typically involves removing the drain (An important step that improves coating life-span but is not always possible) and repairing any damaged areas, including checking to see if the bathtub holds water after draining. Chips or cracks are repaired using Bondo or another type of polyester putty. After repairs are made the surface is prepped with an acid etching. Etching and wet sanding provide mechanical adhesion and clean the surface. Porcelain, enamel, and fiberglass tubs are non-porous and do not provide a good substrate for the new coating to attach to. Etching the surface provides a porous surface that will allow proper adhesion. Another possible method is to apply an adhesion-promoting bonding agent like silane to the surface before applying the coating. The two methods can be used in unison or independently. The greatest adhesion is generally achieved by using both methods together however, some newer refinishing processes claim they do not require the use of etching, by relying on silane alone. After preparing the surface, Prior to spraying any chemical coatings, most refinishers will protect themselves and their clients by completely masking the areas that can be affected by overspray and setting up a professional exhaust system rated to work with the type of coating system being applied. This is important for many reasons, the greatest being a possible fire or explosion hazard. Then the refinisher will use a NIOSH-rated fresh-air supplied breathing apparatus to and spray suite and gloves to protect themselves from the chemicals being used in the process. They also provide assistance with the quality of the spraying.