I have a used front bumper section and fender with some scratches.
Back when I was doing body work as a kid I would degrease, scuff sand and prime then fill the scratches with lacquer putty. However the cars were made of metal. Just wondering if I need to use a special primer.

Also the bumper is pushed in in one place I can pop it out but it falls back in.
Would some mild heat help?

 

Go to where you are buying your paint and talk to them about a good primer that will work with the paint you are going to use and these plastic parts. A lot of the spider web cracking you see on bumpers is from either a primer that does not work well with plastic or a primer that does not work well with the base coat.

Yes heat will help "reshape" the bumper. Also ask your paint supplier about high build primer or a vinyl spray, you do not want to use "spot putty" on these bumpers

 

Oh I never thought of that but the thinners in the fast putty could raise heck with the plastic huh? Nice catch

 

I took the bumper section and used a heat lamp and cold wet rag to reshape the dent and I`m amazed how well it worked. I need to work it a bit more and doubt I will ever get it perfect but its good enough for the girls I go out with as they say. lol