Painting a partial panel (spot repair)
 

I'm fixing a PVC bumper on an RV (I know, not an LS, but still plastic bumper). I've plastic welded and filled with a bumper repair kit. Getting ready for adhesion promoter/primer. I'm going to just tape off the area and and have a sharp transition between primer and original pain (Imron). Painting the whole bumper or to a transition line is out of the question.
My question is, what are the next steps to best blend in an enamel on to existing paint? Mostly interested in surface preparation, sanding, etc on the blend area to get the new paint to stick to the old.
Thanks
Gary

I know the new Imron isn't comparable to the old stuff. I'd only use adhesion promoter on raw plastic, prime & block sand flat as far as you need to into good paint &scuff it with probably 600 to 800 grit a little ways out.. You can fully tape off a ways out & then where you want to end repaint, start a 2" tape strip not stuck down at repaint side to give a softer line when spraying. Then compound buff area later. There are spray solvent blending sprays to help melt in a repair area, but haven't tried them yet. Your old imron is pretty solvent resistant.

Right now the taped off area is a combination of imron, old pvc bumper, plastic welded pvc, and epoxy bumper filler.
Plan is finish with 400 grit in taped area, adhesion promoter then primer.
Remove tape, extend sanded area a few inches with 800-1000 grit.
Spray for a soft edge, then buff.
What's a good buffing compound that will smooth the imron without burning through the new rattle can spray?

There really isn't per say a good one for the 2 different products at the same time. I'd just carefully wet sand finer & finer by hand more so on the harder imron portion. & with a buffer & mostly the edge of a foam pad (going from coarse to finer foam pads) buff more on the imron side working into the rattle can paint.. Careful not to burn the rattle can paint.

OR get a big ole honkin bumper sticker.:poke:

Buffing compounds is a whole other opinionated subject, but if you don't have some fancy selection, meguiars diamond cut compound is a good one. It is a diminishing type compound, meaning it starts out coarse & then wears down to a polishing rouge which ends up cutting much finer. Used properly a diminishing type compound is great especially for spot repairs. Coarser to finer foam pads all play into cutting action, be careful with coarse ones on the new paint.

Thanks for the info, I'll give it a shot.