Painting over painted door

[thesmoothound]

Hi.
I need to paint over my internal door with gloss. It is gloss alreay but has yellowed a bit. Do I need to undercoat again?
Thanks

 

[sparkwright]

Yes, you need to sand first.

Assuming you want white, apply one undercoat. If it looks like the yellow has not covered, put a second undercoat on. If you have a good solid white finish, then apply the gloss.

 

[thesmoothound]

That's great advice, thank you.