Fact Finding with a circular sander

[randywebb]

I discovered that an air powered sander is great for getting down to the truth...

Here is an example of what happens if the PO wet sanded the primer instead of doing dry sanding only as is supposed to be done.

The small pock marks are thousands of pin hole rust spots from the pores in the primer. The smooth areas above and below have had the pits polished out.

The surface top coat had thousands of tiny bubbles in it. I paid a "mechanic" (a professional - but only in the sense that he charges people money) to evaluate this car. He claims he ran a diaper over it and looked it over carefully.

Sure.

(BTW - I have no artistic abilities and am not doing the body work/painting. A shop here in town is doing it.)

[randywebb]

Here, the bondo goes all the way thru to the inside of the rear fender - an area that is wet for at least 7 months of the year. These should have been filled with metal.

Not sure what would cause these 3 evenly spaced holes in the first place -- kid with an ice pick??

[Jim Garfield]

I think someone poked the holes to get the Bondo to grab better, or pull the sheet metal out.

[cygtoad]

Maybe one of the previous owners was a drug pusher and they are bullet holes from a deal gone bad.

[gorfllub]

Speed Holes! Sweet!! They lighten the car so you go faster!!!

[Bob's Flat-Six]

That's an expensive bummer Randy.

I'm puzzled why so many of these cars get taken down to bare metal in the first place for a repaint. I guess if it has been painted so many times it might be necessary or for a color change?.
IMO it's so hard to reproduce the factory paint process especially on the later cars that were galvanized that I'm not sure what is being gained if anything by stripping them.

Porsche paint process on 1980 SC

[dgagne]

I wouls suspect the holes were used to pull the metal out, was the rear involved in an accident? You will probably find more bondy around...you can always take the wheel off and look up in the wheel well to see if it is straight or not...good luck!

Derek

[randywebb]

Pulling the metal out makes sense - I should have thought of that.

Thanks for the kind thoughts. This '73.5 shouldn't have had Thyssensteel for the body sheet metal. I guess people sand to bare metal to amke sure they get all rust - dunno.

So far no surprises have been found that increase the price of the job....

The other thread on this car's body work (antenna hole thread) has a pic that shows some pretty thick bondo - we'll see what's up with that as the sanding progresses.

[exhaustfumes]

i have painted quite a few cars, including my 77 911, and wet sanding primer is fine, as long as it is 100% dry before painting top coats. wet sanding gives you the best removal of grit and particles. i might guess those pinholes are from water in the primer, or surface rust beneath the primer that came thru after sanding. i painted the 911 in 1997, and other than some areas that see high heat (above the oil tank), the paint job still looks like new.
meticulous prep is the key to a good paint job.

[wholberg]

Originally posted by randywebb
[B]Not sure what would cause these 3 evenly spaced holes in the first place -- kid with an ice pick??

...and we journey back in time...

"Dang! That radio antenna is too high...Now it's too low...There we go."

[randywebb]

I'm just passing on what the painter told me - he's supposed to be the best guy in town and is about 60 or so - been around a while. He said the primer is supposed to be dry sanded only (maybe he meant that particular primer). The primer says on the can "Dry Sand Primer." He said that primer didn't use to have that on the can, and that the PO didn't use a metal prep. either. Also, the primer was on really thick.

[cygtoad]

The practice of putting holes in cars for dent pulling and body work has gone by the wayside. What they do today is weld a dent puller to the suface and then pull the dent. Then they grind down the weld. This may have been well done work, but my guess is that if someone who knew what they were doing did the work, it was done some time ago. It seems to have held up.

[randywebb]

yeh - I've seen those special guns for that - very trick

It does seem to have held up - the painter told me they should not have had the bondo go all the way thru the fender into the wheel well. He has a thing that welds a washer or plug there and is going to do that.

[dgagne]

I have always wet sanded epoxy primer and has had great results, getting the primer as smooth as possible results in a much better paint job. Don't see any problems wet sanding primer.

Cheers,

Derek

[geof33]

Gotta agree with the wet sand primer thing... I've always been told to. Definatley no expert... but that is what I learned... at least with an epoxy primer/sealer.