I've been been asked to fill a small chase in a kitchen by a customer and as a decorator rather than a plasterer its not something I've done before so would appreciate any advice. It's an external wall and they've used an oval PVC capping. Since it's not that deep, do I need to bother with bonding/render or can I just go over it with Easy-fill or even powdered filler? I want whatever I use to 'key' properly to the plastic. I've attached a photo.