Crumblin' Mud, Filler Failure, or Bad Bondo Bond?

[RottenRodney]

So what do y'all make o' this?



See the crumbly, tough-to-feather edge?

The car was stripped-to-metal and very agressively sanded with 80-grit on a DA. The DA hasn't been oiled since it left the Hutchins assembly line in 1978. Our compressed air is clean as are our hoses. After sanding, the metal was further cleaned using acytone and Kimberly Clark (Wypall Plus?) white, disposable toweling 'til the bare metal nolonger turned the white toweling black. The car is totally isolated in a surgically clean stall and I'm an absolute freak about contamination so I think we can rule out dirt, oil, moisture, etc.

It's had adheasion problems from the gate. I first noticed it with Rage Gold in 40-grit. What you're lookin' at now is after skimmin' with Quantum 1. First a few passes with 40, then through 80, and now it's in 120 -- that's 120-grit 3M Gold.

Usin' light pressure and sharp paper, that's about as feathered as I can get it. Do ya s'pose the 80-grit-sanded metal just ain't toothy enough this time?

Thanks for your input.

RR

[Len]

I've had that problem before and never knew what caused it. My mentor once told me that steel that has been heated with a torch or was in a fire may not hold filler properly and I should epoxy prime it then apply filler or a filler primer.

[bluerooster]

Photo is too fuzzy to really make out anything but the finger.
But what you describe; I've had happen. And can be troublesome.
I would remove all the filler, prime with epoxy, and start over.
Is the surface steel or aluminum? It makes a difference.

[RottenRodney]

Photo is too fuzzy to really make out anything but the finger.
But what you describe; I've had happen. And can be troublesome.
I would remove all the filler, prime with epoxy, and start over.
Is the surface steel or aluminum? It makes a difference.

It's steel. It's a big job too -- not the kind ya'd want to start over on. Back to the fuzzy photo; right directly above the finger is the little crumbly spot. Anyway, it acted better in finer grits. I feathered out into 220 before priming with 5-Star Direct-to-Metal. It's lookin' real good right now, but in the back o' my brain I'll remember the problem.

If ya know somethin' I don't, please let 'er rip.

Thanks,

RR

[CoolasIce]

One more thing.
Oil that DA buddy.