Plastering over painted aluminium led trim

To bond plaster to painted aluminium LED trim, first clean and lightly sand the trim to create a key. Then, apply a specialist non-porous bonding agent like Thistle Bond-it or SBR primer, which provides a gritty texture for grip. Once cured, apply the plaster over the primed area for a strong, seamless finish.

Depending on where this trim is situated I’d use Expamet it’s a stainless steel or galvanised metal that would be fixed in place then rendered/plasterd over it gives a good strong background to bond to

Lightly sand the painted aluminium, clean it, add a bonding primer (PVA or gritty primer), optionally add mesh on edges, then skim. That’s it.