Do I need to undercoat?

[dazzystar]

Hi All,

Going to be painting all my sills and window frames. Going from a dark grey satin to white satin. Apart from giving everything a good rub down and caulking around cracks, do I need to apply an undercoat as some leading brands say not needed but would rather ask the professionals who do this every day. Also, do I caulk before or after undercoating / top coat?

Cheers
Daz

 

[Wayners]

I always caulked after undercoat as caulk stuck better.
Waterbased satin will stick to old waterbased stain. Same goes for gloss.
As a general rule I always used an undercoat.
On old oil gloss use an adhesion primer.

Yeah it's said you don't need a primer with 180 grade sanding and a clean with a paint cleaner, but I always found it's a better job if you do use a undercoat.