U-POLGrip#4 Universal Adhesion Promoter, Automotive Spray Paint, Durable & Long-Lasting, Easy-to-Use, Clear, 12 OZ

Seems to help the paint adhere well. Only time will tell how long since the parts were plastic, metal and rubber. I even used it to help paint my wipers!

This stuff really helps with getting stuff (like Velcro) to stick to plastic.

This is a very versatile adhesion promotor. You can use it directly over metal, painted surfaces, plastics, etc. I used it over ABS and Polypropylene plastics and also over primer that I couldn't sand adequately for base coat. Once, I forgot to spray it on a piece that I already started painting. I know Bulldog can be used as an additive for paints, primers, and clear coats, so I just sprayed this over the wet primer as a test. I have no idea if it helped at all, but it didn't case any weird reaction, fisheyes, etc. The price of this is much better than Bulldog but is also as versatile and compatible with many surfaces and paints.

Had great adhesion on metals, on poly it made the finish come out fish eyed. I like Bulldog from Kleen Strip, but this stuff works good for urethane bedliners

But it worked perfectly fine. I sprayed lots of spots on the jeep I was worried about and it worked out really well.

Bonded well to bed liner on the bumper. After letting it cure I was doing some off roading and slid into an oak tree and hit the bumper pretty hard. Not a single chip.

I decided to paint the polypropylene fenders and side panels on my 13 year old KLR650 with Raptor liner. The sun had faded them to a dark pink. The instructions for the Raptor liner required the use of Grip #4 adhesion promoter. As far as I can tell it did exactly what it was supposed to do on a difficult to paint surface, which is to encourage a strong bond between the paint and surface. The stuff is water clear and and doesn't appear to have any solids in it. It's a mix of organic solvents that seem to slightly soften the plastic surface for 20 minutes or so.The stuff isn't cheap. Was it necessary? It's hard to know but the time for prep and the expense of the Raptor coating justified it in my eyes.

Works great!