Painting over silk emulsion

[DIYedboy]

A mate at work emulsioned over his shiny silk emulsioned walls, a few days later it started to flake off.
He was advised to sand it off (the new paint) and then apply a special primer which he has done.

I'm amazed.............is silk emulsion usually that problematical?

 

[Grenage]

Yes. You might get lucky, but generally smooth shiny surfaces need to be roughened some with 120 grit or the like.