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What's the best way to prevent surface rust b/w sandings?

I am now at the stage where I'm laying down filler primer and wet sanding it off. Because I'm doing this in my spare time, often a week or two will pass between when I wet sand and can re-prime for another sanding. And, being a novice, I occasionally sand down to bare metal, particularly on the first coat around the edges. The panels I just came back to had a bit of surface rust in areas I had sanded to bare metal. I had to treat these with metal conditioner before applying a second coat of primer.

To avoid this surface rust in the future, can I just hit these bare metal areas with etching primer (rattle can) to protect them until I am able to get back to priming again?

Thanks.

Geoff
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Old 08-24-2008, 01:30 PM
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(Former 1968Cayman)
 
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I was using SEM etch primer on everything that wasn't covered with something else. Then I ran out and started using my copper "weld through" primer - giving the car a somewhat pimipish look- but I've now resorted to using whatever primer I have lying around since I decided to strip it completely (again) once the metal work is done. It hasn't started rusting yet, although I've kept the garage shut for the last few weeks and have a dehumidifier on standby for bad days. In the south, I'm told that it is possible to get surface rust in as little as a half-hour during the summer.
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Old 08-24-2008, 02:08 PM
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Have you considered dry block sanding ?? Wet sanding is not really necesary at this point. I used 180 on my first coat or two and then 400 dry. I next went with 600 dry to get it really smooth, but you can stop at 400. Still some sand through initially, but they don't rust up as quick when you go dry.
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Old 08-31-2008, 08:50 AM
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Quote:
Originally Posted by rw7810 View Post
Have you considered dry block sanding ?? Wet sanding is not really necesary at this point. I used 180 on my first coat or two and then 400 dry. I next went with 600 dry to get it really smooth, but you can stop at 400. Still some sand through initially, but they don't rust up as quick when you go dry.
Actually, after finishing up with the doors and hoods and moving onto the main body/fenders, I found that, like you, after the first coat a dry sanding of 180 grit worked better. I just sprayed on a second coat of primer yesterday and wet sanded it down this morning with 320. I did sand thru in a few spots around the fender lips, but I hit them with metal conditioner right after I was thru.

I still have a bunch of pin holes here and there in my primer. Not a ton, but enough to annoy. I am not going to paint the car myself, so I think I may give it to my painter to do the final prime/sand to make sure its done right.

Thanks.

Geoff
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Old 08-31-2008, 11:23 AM
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If you are doing some of the work, doesn't your painter want it to be ready to paint instead of them having to do it? Taking your time like you are doing can result in you bringing him something they can take from you and complete well, or else they have to do it themselves from scratch. If for any reason, mostly to know it has been done right.

You are on this forum and can do it right. Are your fingerprints going away, and your hands hurting? If not get back to work and yhey will.

You can properly get it ready for him, by leaving it fully sanded with 400 wet. As a rule always prime (or paint) after you sand. Of course, you don't have to prime the whole panel everytime, just enough to cover the stripped metal, and anybodywork and bare metal exposed during sanding.

Purchase supplies from an automotive paint supply store if possible. Use best primer can get hands on. Stay away from most rattle can types, but there are a couple good ones (yes self etching is ok, but once applied can use filler primer there after including for any small sand through areas.

Don't leave your work with pin holes. You can fill pinholes by sanding and repriming or sparingly using professional grade glazing putty . I would use the following sand grits; 36 (grinding disc), 40 dry (bodywork), 80 dry (primer), 180 wet (primer), 400 wet (primer). Sounds like you are in the priming stage prior to the 400 wet. It benefits you to sand with 400 wet on a sanding pad, and inspecting for blemishes- dings, scratches and pine holes- once you find them and, re-prime and sand panel can be perfect (ie ready) for paint. Once you have sanded it and it it good, you should apply a layer of finish primer. This finish primer may be final sanded with 400 prior to painting. BTW if you leave your car in primer for a couple of weeks before you sand your finish primer, you can also be more assured your finish will not further swell revealing blemishes because as time proceeds the undercoat solvents evaporate, and undercoat/bodywork swells/settles. Uses sanding blocks and pads, and take your time. You can do it. Save your painter any grief and yourself, for that matter because he is going to let you know One way or another) if you bring him a surprise.

Oh and if you get this far, let me tell you, you can paint it yourself too.

Goodluck!
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Last edited by BReyes; 09-01-2008 at 08:35 PM..
Old 09-01-2008, 08:30 PM
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Bernard,

Thanks for the great advice. So here's where I'm at: As far as sanding goes, I pretty much followed your process so far, 36 grit on the body work to shape it, 80 grit to smooth it before laying down primer, 120 grit dry on the first coat of primer (with guide coat), then 320 grit (wet) on second coat of primer (with another guide coat). Sanding pads/blocks/PVC pipe all the way. Aside from a couple little divots here and there (that I have/will take care of with polyester putty), all major imperfections have been taken care of now. I have been going around the body and panels with a trouble light and tube of glazing putty filling in any little pin holes or other imperfections in the primer coat. If you can overlook the little dabs of glazing putty here and there (that I have yet to sand out), I have to say that its looking pretty nice right now.

All my supplies have been purchased at a professional body supply shop (they suggested final sanding with 320 grit). I'm using PPG supplies and have used Shop-Line metal prep system followed by the epoxy primer and filler primer. I was only inquiring about whether it would be acceptable to use a self-etching rattle-can primer on those small patches of exposed metal when I may go a few days b/w wet sanding and priming.

Yes, I have considered painting it myself, but I have done some painting before and know that if you're not careful you can produce a mediocre job very easily. I've spent a lot of time preparing the car up to this point and want a perfect paint job.

Again, thanks again for your great comments - its good to hear that I'm on the right track and will produce something ready for paint. Maybe I'll pick up some 400grit for the final sanding.

Geoff
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Old 09-02-2008, 04:26 PM
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