Regular maintenance for a granite composite sink typically consists of wiping a special coat of sealer on the sink surface once a year and spraying a stone-cleaning solution on its surface once per day. Use a pH-neutral granite cleaner, treating the sink as if it consists entirely of granite, rather than a composite.
Granite composite sink manufacturers typically build these sinks out of a combination of granite and a plastic resin at a rate of 90 percent granite to 10 percent resin. Cleaning solutions made from citrus juice, ammonia or vinegar can strip the finish off of a granite composite sink. Even though the resin composition of a granite composite sink offers greater durability and reduced porosity, these fixtures can become etched just as easily as pure granite sinks.
When spraying the sink with a pH-neutral stone-cleaning solution, wipe the cleaning solution off immediately after spraying so that any stains or mineral buildup that may be present on the fixture gets removed. Otherwise, stains can seep into the granite and become difficult or impossible to properly remove. Generally, hard water and food stains manifest as a tough white film that you cannot remove by scrubbing. Wipe the sink off with a dry cloth after each use to ensure that this film does not develop.