Auto body repair & detailing: blending in a paint job, paint cans, old paint


Question
Hi, You misunderstood my main question. I was wondering how
I could fix the section in between the new job and the old paint/clearcoat already on the truck without doing the whole fender. There is a small section that didn't get painted. I am using small paint cans to spray the paint and clearcoat. Can I mask over the new job and the old good section so I can paint/clearcoat the small scratched section and then try to blend it into the recent job and into the old good good section of the fender. Will the masking tape ruin my just recent job and will there be a line where my recent job meets the next spray job? I don't know if I should use polishing compound to smooth out the edges of the recent job first, mask off section of the recent job a little further out onto the old good fender section and then just paint over the edge covering a little bit of the clearcoad and out a little out covering the scratches. Then clearcoat the same area.
Also, I do not have a buffer, so I will just be using polishing compound and a rag to buff in the edges of my recent work.
Thanks
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The text above is a follow-up to ...

-----Question-----
Hi,
I cut out a section of metal, fiberglassed it, filled in with bondo, glazing putting, primed, and then I sanded a little past the primed area to blend in the primer. I then painted 3 coats of black paint and 2 coats of clearcoat on that area of fender only of my dakota. I did not paint the whole fender and some experts say....I didn't want to ruin the rest of the fender which is good...When I removed the masking and paper, I just noticed that I didn't mask far out enough on one corner leaving a strip of scratched paint 3/4"W and 4"L between the new paint job and the old paint. How can I fix this?
Do I have to wait for a week to polish the new job into the old job and then mask the area off, spray paint and clearcoat or should I correct the problem right off? Could I just blend in the scratched paint area?.....It would not be a problem if it was just paint that I sprayed, but the clearcoat may cause problems.
-----Answer-----
Aaargh! Okay, I'll try to help. You should be able to get on the paint right away. First, you won't ruin the old paint by painting over it, unless you are using spray can paint. If you are using a spray gun, do this- fix and prime the spot. Sand the prime with 600 wet, as well as the blend out, to remove any roughness. Take a grey scotch brite, and scuff the entire fender. Now, only color coat the repaired area, until hiding is achieved. Arc the gun out, so that color sort of flies out past the colored area. It will be dry sprayed, but that is okay. Once the base dries, tack off the fender well with a tack rag. Now, clear the entire fender. If you don't like the paint match, you can blend into the door, using the same fanning out technique. You will only partially color the panel, but clear the entire panel. That is how a true pro does it. "spotting in" a panel is a horse shit way to paint it, and even a pro job will show thru in a very short time. If you are using spray cans, then yes, keep it small. A week is too long for letting the paint set up before polishing. I would polish the blend within 2 days, or the paint will get too hard to polish out without a buffer. Let me know if this helps. Bill

Answer
Joe, what's to understand? You have a flaw in the paint you can't live with. Repaint it! I gave you complete instructions for spray can, and spray gun, on full panel paint, and on spot jobs with a rattle can.  If it looks bad, repaint everything again, even what looks good. I think you believe that there is some magical trick I have to fix this flaw. THERE IS NONE. My way will look great, and last longest. Maybe you should have a body shop paint it for you. Good luck to you, and Sorry you couldn't understand the directions. Bill