Bit of an issue, contacted the guy in Germany who sells the aluminum plates coated in PEI and he said that he’s only able to coat specially anodized aluminum plates.
So the anodizing process creates pores for the PEI to stick to, without it it would just peel off.
Makes sense that you’d want a lot of surface micro-roughness. I wonder if there are other materials that adhere PEI better than aluminum that could be used instead? PEI-coated glass? Hmm.