Which of the following precautions is NOT advised when handling sealants?

Mixing expired sealant is the correct answer because it poses significant risks and is not advised. Using sealants that are past their expiration date can lead to poor adhesion, reduced effectiveness, and potential chemical reactions that might compromise safety and the integrity of the seal. Properly handling sealants requires ensuring that the materials are fresh and within their shelf life to guarantee optimal performance during application.

The other precautions, such as using protective gloves, keeping the work area well-ventilated, and avoiding contact with flames, are all essential practices when working with sealants. Protective gloves help prevent skin exposure to potentially harmful chemicals found in sealants; good ventilation mitigates the inhalation of fumes, which can be hazardous to health; and avoiding flames prevents fire hazards due to the flammable nature of some sealant materials. These practices contribute to a safer working environment when handling these substances.