Older boats, or those with less well-maintained topsides and decks, might require chemical and/or abrasive cleaning and polishing prior to waxing. In such cases, less is more, which means trying to remove as little gelcoat as possible during a more aggressive cleaning process. The good news is that gelcoat is much thicker than a paint finish, but over the years, wet sanding and/or too much use of abrasive compounds will prematurely remove the coating.
When a deeper cleaning is necessary, and stronger acids, bases or solvents are handled, wear heavy-duty dishwashing gloves and try to keep the chemical use as localized as possible. Older, oxidized surfaces are harder to keep clean and are porous enough to soak up stains from tannic acid (the ICW merit badge). Stain-remover products from Star brite, 3M, Marykate, FSR, Boat Brite and oxalic acid (available at West Marine) chemically clean the surface, but over time it will continue to become more porous. Compounding and waxing helps to lessen porosity.