Sealer goes on just before color, spray it wet on wet, meaning spray on a coat of sealer, let it flash, then go straight to color. You don't always have to use it. It hides things.
In a flat rate collision shop, we use it on new parts, I sand them usually with 400, spray on a coat of sealer, let it flash, then go directly to color.
Some metallic colors, like silver sometimes will show sand scratches. The sealer will eliminate that,
It will also give you a uniform base, for colors that wont cover very well.
Primer Surfacer is for over bodywork, bare metal or old paint work.
Epoxy is for the best corrosion protection you can get.
You can use it as a surfacer, but it takes longer and harder to sand, that's why it's recommended to use a regular primer surfacer, or high build primer over it for blocking & final sanding.
you can also use it as a sealer, some brands only recommend it as a sealer for single stage only, (check the technical info) You can also do body work over it.
One good thing about epoxy, is that if you had to leave something in primer out doors for any amount of time, it wont rust for a long time.
Last edited by JeffL; 09/07/2014 3:43 AM.