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Confused on adhesion promoter

I have a question about need of adhesion promoter before epoxy primer. These are body side moldings and labeled as being made of urethane. I put a piece of it in water and it sinks. The label said to use adhesion promoter. Is the float/sink method pretty accurate?



Trying to be the best me, I can be
That label is generalized for all plastics. Mainly so when people paint/prep the stuff wrong and then complain to them they can say that they gave the "proper" advice on the part.
If they are urethane and you have done the test with a sliver of the part, and it sinks, then no, you don't need to use Ad-Pro. I would use SPI Epoxy on the parts as a base though. Far superior than using 2K urethane. If they are bare wash them with detergent or scuff-stuff and a red scotch-brite pad. If they are primed, scuff/sand them thoroughly with 320, followed up with detergent or scuff-stuff using a red pad. Then 2 coats of SPI epoxy. That will give you the absolute best adhesion.
Thank you. Yes a piece does sink, and they are new nothing on them. They are listed as urethane but have no way to verify that. I’m going to wax/grease remove them and take scuff stuff and scuff pad to them before epoxy.