The PM accepted a CE for side entry treatments / table tops. The Contractor suggested a material change to increase the durability. The PM accepted the proposal but then rejected a subsequent NCE for the additional cost of using different material, stating it was not valid as it was a Contractor Proposal. Is this correct?
It doesn’t sound like it.
For the side entry treatment /table tops the PM would have to instruct a change to the Works Information (NEC3) / Scope (NEC4).
Providing the PM then instructed the further change to the material to increase durability, then that would be an additional instruction changing the WI/Scope and hence an additional compensation event on top of the original one.