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Envious
Samba Member
Joined: January 08, 2003
Posts: 1821
Location: Toronto, Ontario, Canada
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 Posted: Wed Nov 06, 2013 7:18 pm Post subject: Preventing flash rust when wet sanding final prime |
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I'm almost ready for paint and I'm blocking the car with 400 wet. While I'm working in the fender wells, I'm hitting the occasional high spot. What can I do to prevent flash rust while I'm wet sanding the rest of the car. I realize that I have to hit the bare metal spots again before I paint but I was hoping to not have to mix primer and clean the gun just to hit a couple of little spots.
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71 Type 1302 Custom
64 Type 151
63 Type 117 L469 Anthracite
64 Type 361 L575 Nutria
64 Porsche 356c
56 Type 113 L227 Strato Silver
52 BSA C11G
59 Heilite Single Wheel Camping Trailer
56 Allstate Single Wheel
84 Vanagon Westfalia
http://www.thesamba.com/vw/forum/viewtopic.php?t=388225 |
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c21darrel
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Joined: January 22, 2009
Posts: 8211
Location: San Dimas
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Envious
Samba Member
Joined: January 08, 2003
Posts: 1821
Location: Toronto, Ontario, Canada
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| Posted: Thu Nov 07, 2013 11:39 am Post subject: |
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Will it affect my primer or cause issues under the paint.
_________________
71 Type 1302 Custom
64 Type 151
63 Type 117 L469 Anthracite
64 Type 361 L575 Nutria
64 Porsche 356c
56 Type 113 L227 Strato Silver
52 BSA C11G
59 Heilite Single Wheel Camping Trailer
56 Allstate Single Wheel
84 Vanagon Westfalia
http://www.thesamba.com/vw/forum/viewtopic.php?t=388225 |
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Northof49
Samba Member
Joined: July 22, 2013
Posts: 1759
Location: Winnipeg, Manitoba, Canada
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| Posted: Thu Nov 07, 2013 12:08 pm Post subject: |
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Just sand off the flash rust to the extent that it occurs. As you said, you are going to prime the high and bare spots again prior to paint.
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1958 Karmann Ghia owner |
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c21darrel
Samba Member
Joined: January 22, 2009
Posts: 8211
Location: San Dimas
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| Posted: Thu Nov 07, 2013 12:45 pm Post subject: |
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 Its called etch and prep . It is made to do exactly what you want.
The Klean-Strip 1-Gallon Phosphoric Prep and Etch removes rust from iron and steel surfaces and treats metal surfaces for good paint adhesion. The treatment also etches concrete to allow paint or stains to penetrate and adhere.
•Efficiently removes rust from metal surfaces
•Etches concrete and masonry surfaces
•Helps ensure good paint adhesion
•Inhibits flash rusting
•Non-toxic formula |
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Northof49
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Joined: July 22, 2013
Posts: 1759
Location: Winnipeg, Manitoba, Canada
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| Posted: Thu Nov 07, 2013 2:22 pm Post subject: |
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What if its applied over existing primer? especially thin spots where it might penetrate to the metal substrate. Not saying it won't work, but its clearly intended for preparing for paint to be put over it after it finishes its effect on the metal. I would be worried it might lift the primer where its thin. But then again I worry about the wrong things all the time.
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1958 Karmann Ghia owner |
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c21darrel
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Joined: January 22, 2009
Posts: 8211
Location: San Dimas
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| Posted: Thu Nov 07, 2013 3:52 pm Post subject: |
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| I typically over-worry too North. I used the phos acid as i was block sanding my ghia. Block sanding took me about 9 months and the project was stored in a garage. I would apply to bare metal on my sand thru spots quickly with a tooth brush. On spots i didnt hit i got flash rust...which the phos acid also quickly removed. I never had any issues during or after. I was using all PPG stuff dp40, k36, concept ss. |
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Northof49
Samba Member
Joined: July 22, 2013
Posts: 1759
Location: Winnipeg, Manitoba, Canada
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| Posted: Thu Nov 07, 2013 8:28 pm Post subject: |
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| c21darrel wrote: |
| I typically over-worry too North. I used the phos acid as i was block sanding my ghia. Block sanding took me about 9 months and the project was stored in a garage. I would apply to bare metal on my sand thru spots quickly with a tooth brush. On spots i didnt hit i got flash rust...which the phos acid also quickly removed. I never had any issues during or after. I was using all PPG stuff dp40, k36, concept ss. |
Thanks, better to know its a tested technique.
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Envious
Samba Member
Joined: January 08, 2003
Posts: 1821
Location: Toronto, Ontario, Canada
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| Posted: Fri Nov 08, 2013 7:23 am Post subject: |
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| Northof49 wrote: |
| What if its applied over existing primer? especially thin spots where it might penetrate to the metal substrate. Not saying it won't work, but its clearly intended for preparing for paint to be put over it after it finishes its effect on the metal. I would be worried it might lift the primer where its thin. But then again I worry about the wrong things all the time. |
Must be a Canadian thing. I had the same concern  I'm not expecting to hit any high spots on the main body, doors, fenders, etc, but I'm blocking the fender well areas which are really nice but not perfect. I had to draw the line somewhere.
I'll get some today and try it out. Thanks.
_________________
71 Type 1302 Custom
64 Type 151
63 Type 117 L469 Anthracite
64 Type 361 L575 Nutria
64 Porsche 356c
56 Type 113 L227 Strato Silver
52 BSA C11G
59 Heilite Single Wheel Camping Trailer
56 Allstate Single Wheel
84 Vanagon Westfalia
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W1K1
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Joined: March 04, 2004
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Location: Southern AB
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Bobnotch
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Joined: July 06, 2003
Posts: 22410
Location: Kimball, Mi
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| Posted: Thu Nov 14, 2013 11:09 am Post subject: Re: Preventing flash rust when wet sanding final prime |
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| Envious wrote: |
| I'm almost ready for paint and I'm blocking the car with 400 wet. While I'm working in the fender wells, I'm hitting the occasional high spot. What can I do to prevent flash rust while I'm wet sanding the rest of the car. I realize that I have to hit the bare metal spots again before I paint but I was hoping to not have to mix primer and clean the gun just to hit a couple of little spots. |
What kind of primer are you wet sanding? If it's DP epoxy, then you could always hit those spots with a reduced layer of DP primer (reduce it up to 10% with DT reducer), and shoot the car in color (or your high build primer). Or even wait a day, and lightly wet sand those spots to blend them. That's one of the things I like about working with DP epoxy primer, you can adjust as you move along with a type 3 project. 
You could also wipe the areas (that you sanded thru) with PPG's DX580 metal conditioner, and remove any flash rust, then re-prime those spots.
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71 Notch ...aka Krunchy; build pics here;
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