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Old 07-31-2012, 04:22 PM
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sandscratch swelling/ buffing

ok, this might be a little long winded....
had this happen on two cars...black and dark green, bc/cc, omni products.and featherfill...

the issue occurred while buffing, the paint was sanded smooth,finished to 1500 grit.

1st pass with compound, white pad,about 2000 rpm.
paint slicked right up, but then noticed what looked like scratches, only a couple, if there ws any bondo at all in this spot it was very thin, maybe a hail dent......car was d/a stripped, epoxied, rage in a couple spots, and then a coat of featherfill. blocked with 80 lightly, then 180, d/a to 220, then urethane primer....then wet sanded to 400-600. car had days in between, coats. when color sanded, it was opened and sat in the sun a couple days.

so...I sanded this area, buffed again, it was slick, then about 30 minutes later...scratches!.
so,,,,it appears that the scratch (swelling) happens when i put the buffing heat on that spot,,,it swells, looks like a scratch, I sand,,,(which is actually sandin a swell) then after buffing it shrinks and makes an actual low scratch..
so then...I sanded the area smooth again, used 3000 grit, and lightly buffed with black pad..this time got NO swelling...so its just a matter of pulling it out into the sun and seeing if it will swell and show scratches.

finally...the questions,,,

whats the deal? I dont think it's trapped solvents, I dont think its air in the bottom of a scratch, I think its 2 different materials expanding at different rates...if it is that what's the fix?
SHINE...before you tell me to lose the urethane and featherfill, know that I already have comitted to epoxy only on the truck I'm doing! lol!
but, even if I used epoxy instead of urethane, wouldnt I see the same problem?
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