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Thread: Color Sanding Blues

  1. #1
    Join Date
    Apr 2010
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    Sacramento, CA
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    124

    Default Color Sanding Blues

    Hey Guys
    OK, I've been dying to try some of the body work and paint tasks that I've studied and read over past few months. I picked up a junkyard fender and hammered out the dents, filled, filled, blocked, polyester putty filled, primed (2K), and blocked. Then primed, painted with PPG DBU (with hardener), and cleared with PPG Concept 2002.

    It came out really nice. Color and clear layed down smooth with very minor orange peel. I used Devilbis Starting Line gun, 1.3 tip. (yes, cheap gun, but worked pretty darn well).

    To further my experiment, I tried to color sand and buff the fender. That's where things didn't go so well. I color sanded with 1000 grit and 2000 grit (by hand using a 5" durablock). That worked fine and removed the minor orange peel and imperfections from spraying outdoors. Using a Makita 7-9" Dial Speed Control Polisher (at pretty low RPM) fitted with Meguiars W7000 Foam Cutting Pad (red) and using 3M Imperial Microfinishing Rubbing Compound Medium Cut, I managed to cut through the clear coat in a couple locations with little effort. I followed up with a Meguiars W8000 yellow polishing pad and 3M Perfect-it II Foam Polishing Pad Glaze (dark). The glaze worked fine and the finish was smooth like glass.

    Overall, was very successful except for the holes in my clearcoat. I learned a lot. Any idea to what I should attribute the clear coat holes? I think the red pad was too aggressive (it is really hard foam) and maybe the medium cut rubbing compound is also too aggressive? Thoughts?

    I plan to paint my entire 59 Triumph TR3 and feel like it can do it well, based on my limited excursion into body work and paint. But the color sanding concerns me. Thoughts and opinions much appreciated. Alternative products/recommendations welcome.

    Regards,

    Pat
    Sacramento

  2. #2
    Join Date
    Feb 2006
    Posts
    388

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    Plenty of guys will probably disagree with me but I would get rid of the foam pad for the initial cutting stage. I use wool for cutting and a 3M black waffle foam for the final polish. I noticed (at least for me) that it's very easy to grab/burn the paint with the foam pad. I prefer how the wool reacts for the initial cut. The other thing to mention is to make sure you stay away from sharp body lines etc until you get better at buffing. If you do buff an edge make sure your pad is travelling off of it.

  3. #3
    Join Date
    Nov 2005
    Posts
    41,190

    Default

    Quote Originally Posted by TR3_Nut View Post
    Hey Guys
    OK, I've been dying to try some of the body work and paint tasks that I've studied and read over past few months. I picked up a junkyard fender and hammered out the dents, filled, filled, blocked, polyester putty filled, primed (2K), and blocked. Then primed, painted with PPG DBU (with hardener), and cleared with PPG Concept 2002.

    It came out really nice. Color and clear layed down smooth with very minor orange peel. I used Devilbis Starting Line gun, 1.3 tip. (yes, cheap gun, but worked pretty darn well).

    To further my experiment, I tried to color sand and buff the fender. That's where things didn't go so well. I color sanded with 1000 grit and 2000 grit (by hand using a 5" durablock). That worked fine and removed the minor orange peel and imperfections from spraying outdoors. Using a Makita 7-9" Dial Speed Control Polisher (at pretty low RPM) fitted with Meguiars W7000 Foam Cutting Pad (red) and using 3M Imperial Microfinishing Rubbing Compound Medium Cut, I managed to cut through the clear coat in a couple locations with little effort. I followed up with a Meguiars W8000 yellow polishing pad and 3M Perfect-it II Foam Polishing Pad Glaze (dark). The glaze worked fine and the finish was smooth like glass.

    Overall, was very successful except for the holes in my clearcoat. I learned a lot. Any idea to what I should attribute the clear coat holes? I think the red pad was too aggressive (it is really hard foam) and maybe the medium cut rubbing compound is also too aggressive? Thoughts?

    I plan to paint my entire 59 Triumph TR3 and feel like it can do it well, based on my limited excursion into body work and paint. But the color sanding concerns me. Thoughts and opinions much appreciated. Alternative products/recommendations welcome.

    Regards,

    Pat
    Sacramento
    Unless the orange peel is pretty ugly you should start with 1500 then go to 2500 or 3000 grit. If you're sanding wet be sure to use a rubber squeegee to remove the water regularly so that you can see to stop sanding when the peel is gone. If you sand with 3000 or 4000 grit you don't need such aggressive compound to remove the scratches, a light compound like Sure Finish and foam pad will quickly do the job. The larger pads have a higher "edge speed" than smaller pads and they will remove more material more quickly, we rarely use anything larger than 6" because it gives us better control of the outcome.

  4. #4
    Join Date
    Apr 2010
    Location
    Sacramento, CA
    Posts
    124

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    Thanks Brad and Len

    I think that more color sanding with finer grit (better pre-buff prep), smaller diameter pad, and less aggressive pad and compound would help a lot. This was an experiment for me so I wasn't crushed when I burned through the clear coat. Sort of an expensive experiment but I wanted to shoot with the actual paint that I'm going to use on my car and see if I could do it. I appreciate the feedback and will post photos of my progress, if it ever warms up such that I can paint again.

    pat

  5. #5

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    Most important, how much clear did you spray?
    that's probably your problem, not enough clear.
    (or is that to obvious)

  6. #6

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    All of the suggestions these guys made are good ones. I just thought i would throw in my 2 cents.
    First of all, I REALLY like what you are doing, and I wish there were more people willing to try it out. (then people would understand why it is so expensive to have a shop do it)
    I think your problem is this. The normal recommended number of coats (2-3) of clear is not really for sanding and polishing to make a mirror finish. If you look at a new car paint job compared to the fender you did I promise your fender finish looks way better. The sanding and polishing makes good paint look great, but it also removes quite a bit of clear. So if you want to do a glass smooth paint job you really need to put on extra coats of clear so when you sand it you are still left with 2-3 coats worth of clear after sanding.

  7. #7
    Join Date
    Apr 2010
    Location
    Sacramento, CA
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    Thanks again for all the replies. Although it cost a few bucks at my local automotive paint store, I needed to try and see if I could actually do these repairs and paint. Except for the fact that I sprayed outside (because it was a test, that was easiest) and there was a little airborne debris, the paint job went down beautifully. As compared to new car finish, I probably didn't need to color sand. It looked that good. I just wanted more practice and to see how color sanding improved the finish.

    I had put down three coats of clear. Sounds like I might need to put down 5 coats if I plan to color sand n buff, so that I have two or three coats ultimately remaining. Now I see why it can cost so much for an excellent paint job.

    This is a great forum - great ideas and friendly folks. It's given me confidence to try without fear of really screwing up. I have purchased a Hobby Air unit from Len and his video. Plan to purchase a Plus gun and nice Airvantage sander (and supplies) from him as I go forward with my springtime painting of my car. I'll post some photos in my next post - my work firewall prohibits me accessing photobucket from my desktop....

    Regards,

    Pat

  8. #8

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    3 coats should be enough, uless they were over reduced.
    Sand throughs on 3 coats of clear with 2000 paper would take
    a lot of sanding, except for edges.8)

  9. #9
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    Nov 2005
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    41,190

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    Quote Originally Posted by JCCLARK View Post
    3 coats should be enough, uless they were over reduced.
    Sand throughs on 3 coats of clear with 2000 paper would take
    a lot of sanding, except for edges.8)
    Like you said it all depends on the paint products used. If "good" high quality clear is used then two coats is usually enough but if less expensive products are used then you may need more coats to get the same film build.

  10. #10
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    Apr 2010
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    Sacramento, CA
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    I know this is borderline dumb question, but is there any downside in applying an extra coat or two of clear (other than the obvious time AND material expense)?

    I used PPG Concept Clear 2002 so it was the best product I could afford and was reccommended by the paint shop. Definitely a high solids clear and only reduced per the "P sheet".

  11. #11
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    Nov 2005
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    Quote Originally Posted by TR3_Nut View Post
    I know this is borderline dumb question, but is there any downside in applying an extra coat or two of clear (other than the obvious time AND material expense)?

    I used PPG Concept Clear 2002 so it was the best product I could afford and was reccommended by the paint shop. Definitely a high solids clear and only reduced per the "P sheet".
    When using "good" materials the only down side of an additional coat or two is when it gets hit by a stone the chip is usually larger. Other than that there is usually no downside when the paint is applied to a stable substrate. If the substrate is unstable then the thicker paint may crack more easily.

  12. #12
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    Nov 2005
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    Kamloops. B.C.
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    My experience was very similar to yours. When I first started doing this stuff about 10 or so years ago the hardest thing to catch onto was the color sand/polishing. It takes practise and a ton of patience.

    I get blasted by Len and the others everytime I mention this, but I'm going to throw it out there anyways.

    As you've already noticed, it's not hard to get a finish that rivals that of a new car. But working in the less than perfect environment that us home diy'ers do, there's bound to be some dust and crud. The 1500 and up and the preceding instruction handles that just fine and looks great.

    But if you really want a show car finish, there is an alternate route. Just as you learned in the bodywork stage, you use coarse paper to level surfaces and fine paper to create the correct texture for paint. Same with sanding the clearcoat. On something that I want to look show quality I shoot 4 coats of a good high solid clear. I then go over that very carefully with 400 on a hard block. I am not removing any more clear than you are with 1500, I'm just doing it faster and keeping the surface flat while I do it. Our objective is to remove the high points in the peel just down to the adjacent low spot. That's what I do with the 400. Then I block with 800, then finish by machine with the 1500, 2000. At each grit change all I am removing is the previous grit sand scratch.

    The difference in the finished product is the reflection you see. The image you see will be completely distortion free. Take a look at some of the photos you see in hot rod magazines. Before I understood all of this I thought that somehow they were getting a superior shine to make it look that great. But that's not it. It's a distortion free reflection that makes it stand out.

    Anyways, may not be what you're after and definately over kill on most things we do, but thought I'd throw it out there.

    Steve g

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