Which of the following tests may be required during surface preparation?

During surface preparation, monitoring temperature and relative humidity is crucial because these environmental factors significantly influence the performance and durability of coatings. The temperature of the substrate and the relative humidity of the surrounding environment can affect various aspects of coating application, including drying times, adhesion, and the likelihood of condensation or moisture entrapment under the coating.

Temperature can impact the viscosity of the coating material, subsequently affecting how it spreads and adheres to the surface. If the relative humidity is too high, it can lead to condensation, which may compromise the integrity of the coating application. Therefore, keeping track of these parameters ensures that the conditions are optimal for coating application, which aids in achieving a successful finish.

The other options listed, while important in other contexts, do not directly relate to the necessary tests during the surface preparation phase. Flame resistance, for instance, pertains more to the safety characteristics of materials, while thickness measurement and color matching are typically assessed after the coating application rather than during surface preparation.