TotalBoat Gelcoat can be applied over aluminum, however, it is very uncommon due to the required surface preparation and priming. Another factor to consider is the difference in rates of thermal expansion, which could ultimately lead to cracking or coating failure. Apply TotalBoat Aluminum Boat Barrier Coat as specified in the technical data sheet, and allow it to fully cure before applying gelcoat as instructed in the TotalBoat Gelcoat technical data sheet.