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  #16 (permalink)  
Old 04-03-2009, 11:01 AM
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I don't consider 400 grit a coarse grit, it's boarderline.
For my collision repairs 400 is all I generally need.
But for "show car" straightness, I use 150 on my primer first,
taking most of it off.
Then I reprime and go 400.
Same with clear, I first block with 400 to 600 and then work my way up.
This is only for a show car appearance.
I did different panels on my own car starting with different grits
and the panels started with the coarse grits are definetly straighter
with less urethane wave.
I don't believe following with fine grits takes away from the straightness
of the previous coarse grits, they just smooth it & remove the scratches.
Remember this, coarse grits straighten, fine grits smooth.
they're two different things.
Usually not a concerne until you get into the high end paint jobs.
Then it really shows, especially in the reflections of straight lines,
like lights or elec. wires.

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  #17 (permalink)  
Old 04-03-2009, 11:26 AM
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Are the last pics dry or wet?
If thats dry,man D, That IS slick.
Have you cleaned it yet?If so,how?
Your bodywork "looks" good judging from the light bulb reflections. I always wet my primer down and use the reflection to SEE. Reflections wavey or "wrong" and the paint will be too.You can also see any bad scratches as well.
I personally would not want it "that" slick and would go over it with double stack gray scotch pads with a flat block backer to keep from finger grooving it for the flat areas and by hand on the raised areas. I want a "little" scratch and the scotch pads will be enough but not too aggressive as to screw it up.
I take MY oppinion from using the chrome paints which are sprayed over a slick surface and the adhesion is minimal at best.
There will be varring oppinions on this but if you want a real answer to YOUR adhesion question,Do a test panel and finish as you have here,base it and after it dries,stick some duct tape or good masking tape on it and pull.
THAT will answer your question.
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Old 04-03-2009, 12:19 PM
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Quote:
Originally Posted by Bee4Me
Are the last pics dry or wet?
They are dry as a bone. The only cleaning I've done is just to wipe off the dust with a brush and rag and then for the pictures I went over it with a tack cloth so the dust swirls would not show so much.

I have a little time to think about it yet, but going over it with the gray scotch pads sounds like it might be the best course of action just to be on the safe side.

Also, this tells me that on the remaining parts I have left to do that I should just stick with fairly new 600 paper and not create such a slick surface.
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Old 04-03-2009, 12:30 PM
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IMO your good to go, looks really slick.

Vince
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  #20 (permalink)  
Old 04-03-2009, 05:21 PM
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Clear it now----call it Dove Grey
(okay, I'll stop now )
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  #21 (permalink)  
Old 04-03-2009, 07:00 PM
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Quote:
Originally Posted by dinger
I'm having the same problem. I had some dust after painting the cowl, wet sanded with 600, re-shot, a lot of fine scratches in the basecoat. Would the clear negate the scratches. I quit after the last results (yesterday). never sand base coat unless you re base,base should be untouched when cleared

I'm kind of in the same boat as Dewey right now, I am wanting to do my final sanding, I plan on using 600, wet. Yea or Nay?
600 clear yes but never sand base coat unless you rebase again
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  #22 (permalink)  
Old 04-03-2009, 11:46 PM
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Quote:
Originally Posted by cboy
This may be an exercise if futility since my camera skills don't allow me to show you the primer surface in microscopic detail. Also, I know it is always difficult to read a situation based on pictures...particularly lower resolution internet pictures...but I'm conflicted now between Vince's "followed good practice" and Frisco's comments on burnishing the surface and not using worn paper.

So I'm posting these pictures just to see if based on the reflectivity, folks think they look fairly typical for primer at 600 or if I've burnished the surface way too much and I might be better off going over everything one more time with all new 600 paper.

Vince is certainly right about one thing, I feel at this juncture like I've really gotten after most of those deep sanding scratches left by the coarser papers. Any flaws or scratches really start to stand out when you get a shiny surface like this and you can really find and eliminate them. But as Willys says, maybe I don't need to be removing those scratches in the first place.

Starting to make my brain freeze up.

Roof



Rear top curve



Rear top curve



Side top curve



That is way too smooth of a surface for paint. You don't want it to shine or have any reflections. You want everything dull. If it is too smooth, then you WILL have adhesion problems. When your paper starts to wear out, discard it for a new piece. Use a rubber block, a new piece of 600, wet sand and let it go. Use some gray Scotch Brite around your jambs.You don't want to be able to see ANY reflections off of your primer.
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  #23 (permalink)  
Old 04-04-2009, 09:25 AM
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I still contend that 400, followed by epoxy sealer followed by color, followed by a few clears then polished will give a great finish w/ no adhesion problems. I don't see the need for going to 600 w/ all the inherent problems it seems to bring.

I'll be quiet again.
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Old 04-04-2009, 10:44 AM
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Quote:
Originally Posted by willys36@aol.com
I still contend ....
I have twice asked politely that we keep this thread focused on two very specific questions/issues. It is clear, however, that Willys36 feels compelled to debate a different subject of HIS choosing rather than honor normal internet protocal and refrain from changing the subject, hyjacking threads or disregarding the expressed limitations requested by an original poster.

I don't know how I could have been more specific in my request to remain on topic so I therefore turn this thread over to Willys36 to do with as HE pleases. I will take my question to another automotive site where they honor normal internet protocal.

I thank those who DID remain on topic and I believe they provided the forum with some excellent input and advice on the issues raised in the original post.
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  #25 (permalink)  
Old 04-04-2009, 03:05 PM
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I respectfully submit that my comment is spot on the topic. Your original question began, "I believe the general consensus here is that sanding your primer to 400 grit before painting is OK and that 600 grit is highly preferred." Then you continued with problems arising from using the 'preferred' 600 grit method which don't arise from the 'OK' 400 grit method. I believe it is totally within the spirit of the thread to offer an informed, although from your contention a minority, opinion that the 400 grit method is actually a preferable method. That's sort of what this site is designed for as I understand it but maybe I am mistaken. Seems to me a variety of input from a variety of experiences on a given topic would be nice? I can see if I interjected a discussion of President Hussein or of VW engine tuning you would have a gripe that I was stealing your thread. I don't understand your rage at my offering a suggestion that may help you out of your quandary. I hope you won't stay away permanently just because of my perceived indiscretion. We enjoy your one off creations and it would be a loss if you did leave.

Oh, and it just dawned on me, since you are a moderator, why not just erase my posts? Seems a lot better solution than leaving.

But in the spirit of cooperation, I believe that if you want a 600 grit finish B4 painting, get several pieces of 600 grit paper and when one starts to wear out and no longer removes material giving the finish it is designed to provide, throw it out and use a new piece!
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  #26 (permalink)  
Old 04-04-2009, 04:03 PM
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cboy, I have done some painting, It is my experiance that 400 is fine if you are going to seal over your primer prior to paint. Sealer acts as an adhesion promotor. I have used 600 with no sealer as well, no adhesion problems either way. But.... the car sanded with 600 and no sealer, when it chipped. was twice as big as the one with 400 and sealer. I don't have an answer as to how fine is too fine, but do know that adhesion is better with 400 than 600 IMO. Based on the photos I would recommend gray scotch brite, It looks too smooth to me. I use a method where I sand 2 panels complete, and get a new sheet and do the second panel quickly and do the third panel then with a new sheet with the sheet go over the third panel a second time and do the fourth panel etc. Dont skimp on materials, this stuff is too much work. Your work looks Awsome, but dangorusly smooth. Good Luck.
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  #27 (permalink)  
Old 04-04-2009, 05:49 PM
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600 rt is the "norm" to use today. A few yerars ago with single stage 400 grit was the paper to use. But whether 400 or 600, you have burnished the primer to the point that paint will not stick very well. It may for awhile, but later on down the road you might (or probably will) have problems with adhesion. When i painted my truck a couple of years ago, I primed with 2K primer, wet sanded with 600, gray ScotchBrite the jambs, and shot the sealer and painted. You have primer that is almost as shiny as clear when shot. Way too smooth. Although it may look good to you when you sit back and admire how it looks, it is not appropriate for painting. Get some new paper, cut it into quarter sheets, and rough up what you have. Shoot the paint, clear it, then worry about sanding and burnishing the clear before buffing it out.

C'Boy....not to sound like a Richard...but you have done a hell of a job with the body work. Don't get anal on it now. You have it straight and are worrying way too much about how it is going to look before you get it shot. It needs to be sanded and it needs to have a dull look to it. For instance...take one sheet of 600 wet or dry, tear it into quarters, use one piece, dunk it in water, and start sanding the roof. When the roof is half sanded, toss the piece and get another. 2 pieces and 20 minutes and the roof is good to go. Same with the rest of the panels. In an hour or hour and a half and 4 sheets of paper torn into quarters, you will be there.
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  #28 (permalink)  
Old 04-04-2009, 06:05 PM
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Also, answer your own question for us. Your question sounds like an amateur but you have already done two amazing scratch builts from the ground up so you are anything but an amateur. What did you use on those two successful paint jobs for the final pre-color sand? Whatever that was, why not repeat it on this bad boy?
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  #29 (permalink)  
Old 04-04-2009, 11:13 PM
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I always use 400grit wet before

Painting and i never use sealer.My mentor owns a kustom paint bodyshop where they only due restos no collission work.He always blocked primer with 180 wet then 3 coats off HOK epoxy -uro primer then final sanded with 320 wet.Well from reading tech articles i always thought this was to coarse for final sand but i never said anything because he was the boss i did what i was told. Now that im on my own i still primer and sand like him but i final sand with 400 wet. Never had a problem. He built the george Barris Klone KOPPER KART that was in the Detroit Autorama.A Kustomized 57 Chevy Apache PU.
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  #30 (permalink)  
Old 04-05-2009, 12:02 AM
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I have also used 320 a lot in the past w/ no sanding park problems in the final finish. I think the message to cboy is his pictures are showing too smooth a finish. Purpose of the sanding is to provide a mechanical tooth to the final paint to enhance the chemical one and his polishing 600 is way too fine for the job and could cause the separation he fears. That is my answer to his original question in the thread title, "Grit - how fine is too fine for adhesion?"
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