What should be added when there is a need to rehabilitate a dope coating with cracks, according to the manufacturer's instructions?

When rehabilitating a dope coating that has developed cracks, a rejuvenator is the appropriate choice to address this issue effectively. Rejuvenators are specifically formulated to penetrate and restore the flexibility and adhesion of aged or cracked dope coatings. They contain compounds that help revive the original properties of the dope, making it more elastic and less prone to further cracking.

Adding a rejuvenator is essential because it not only repairs the existing cracks but also prepares the surface for additional layers of dope if needed. This ensures that the integrity of the fabric covering remains intact, and that the overall aesthetic and structural performance of the aircraft covering are upheld.

Other options, such as sealers, primers, and protectants, serve different functions in the fabric covering process and do not specifically address the issue of cracking in a dope coating. A sealer is used to protect the surface but does not necessarily fix cracks. A primer is typically applied before the top coating and would not be useful for repairing existing damage. A protectant may help shield the surface but would not restore flexibility or repair cracks directly. Thus, the use of a rejuvenator is the most effective method to rehabilitate a dope coating with cracks.