Only if you’re working on an older car with a very dull or oxidized finish. All-In-One will not layer on top of itself. In effect, if you apply two coats, you are cleaning the surface twice. This is not required on most vehicles but may improve surface gloss on older, neglected paint finishes. On most vehicles, if you have the time to apply two coats, apply one coat of All-In-One and then a top coat of High Gloss Sealant Glaze.