First of all, it is necessary to determine the cause of cracking. Cracks might occur due to insulation slabs being bonded improperly. Using flexible paint will eliminate the effect, leaving the cause unresolved. The cracks may appear again. For painting mineral wool-based insulations, you should use paints with sufficient diffusivity. You can use Alpol AF 685 flexible silicone paint. However, the applicability of this paint is limited to cracks up to 0.25 mm in width. If some of the cracks are wider, they can be coated locally with AF 645 highly flexible acrylic paint, and then entire area can be covered with AF 685 flexible paint.