primer question

[Jeff Lewis]

does all primer surfacer have to be sanded before applying primer sealer?

[Lost in NJ]

You must read the tech sheets for the paint you are using to get the correct answer.

Generally all paints have a recoat window where the paint has not fully cured. If the paint is not fully cured a new coat can be applied and will chemically bond with the earlier coat.

After that time period you will need to create scratch marks with some kind of abrasive so that the new paint has something to grip onto. Depending on the type paint and such this could be Scotch Brite pad or some grade of sandpaper.