Re-painting bumper covers?

[Tom Nas]

Hi all,

As my beater 80 is now mechanically sound, I'm turning my attention to 
improving its looks. One of the least attractive parts on the car is the 
rear bumper cover that's painted gloss black, not matching the front cover 
which is partly body-coloured as it should be. The reason for the gloss 
black is apparently to cover up flaking body colour paint, probably the 
result of clumsy parking or some other rear-end impact of which there have 
been a few, judging by the appearance of the car.
I've managed to remove some of the flaking paint layers, but getting 
everything off is impossible, it's been primed too well and the paint 
adheres very well to the bumper. How do I cover up the joins between new 
and old paint? Anyone used filler primer (also called high-build primer) 
for this purpose? I would normally use a plastic etch primer to prepare the 
surface, but since there's so little actual plastic uncovered, I thought 
I'd treat it like painted metal.

I'm not looking for a show-quality finish but a used bumper cover at the 
scrapyard is more expensive than a coupla hours of my time and I like to do 
this kind of stuff. The idea is to paint the top portion matt gray/black 
again and the lower portion body colour, like it should be.

TIA for your suggestions...

Tom
87 80- 260k km and counting