Scrim tape or full ceiling scrim

Since the boards are already fixed and screwed into the joists, the main issue is the large number of joints created by using offcuts. Applying 100mm scrim tape to all joints is essential, but given the number of joints, I would strongly consider meshing the entire ceiling before skimming. This will help reduce the risk of future cracking. Make sure all boards are secure with no movement, fill any larger gaps, and use a good quality skim finish. Full ceiling mesh won’t guarantee that cracks will never appear, but it offers much better protection than taping the joints alone. If the ceiling hasn’t been skimmed yet, the best long-term solution would be to overboard the entire ceiling with full-size plasterboards, although that involves additional cost and labour.