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  #11  
Old 10-04-2018, 01:57 PM
rocketman1988 rocketman1988 is offline
 
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Default Oxidation

Aluminum oxidation begins immediately when in contact with oxygen.

It is, however, passivating in that the very thin layer (in the nanometer range) of aluminum oxide provides a barrier between the oxygen and the underlying aluminum.

This barrier then stops, or greatly slows, the oxidation process...
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  #12  
Old 10-04-2018, 02:48 PM
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PokePilot PokePilot is offline
 
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Quote:
Originally Posted by Aluminum View Post
Consider using Van's recommended Sherwin-Williams self-etching primer instead (P60G2). Simply degrease and shoot whenever, no scuffing required.

Splatter is probably caused by air pressure too low. If you don't have massive air supply it is counterproductive to try using an HVLP gun.
I'm pretty happy with the AKZO and I'd like to stick with it considering I've gotten good results with it before. It's really the spray gun that was the issue. When I took it apart I noticed a few of the air holes in the nozzle had gotten blocked by primer. I unblocked every hole I could reach and I still couldn't get the spray to atomize properly, even after experimenting with the air pressure (higher pressures didn't make a difference) and fan width. Rather than continue to waste time and primer trying to fix a $15 spray gun I figured may as well start fresh with a new one.
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  #13  
Old 10-04-2018, 02:54 PM
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JonJay JonJay is offline
 
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Quote:
Originally Posted by PokePilot View Post
I'm pretty happy with the AKZO and I'd like to stick with it considering I've gotten good results with it before. It's really the spray gun that was the issue. When I took it apart I noticed a few of the air holes in the nozzle had gotten blocked by primer. I unblocked every hole I could reach and I still couldn't get the spray to atomize properly, even after experimenting with the air pressure (higher pressures didn't make a difference) and fan width. Rather than continue to waste time and primer trying to fix a $15 spray gun I figured may as well start fresh with a new one.
I have been teased before about my preference for good tools, and my disdain for the Chinese Super Store = HF.

However, in our throw away society..... enough rant.

Clean your gun as best you can by wiping it out, sloshing some solvent around, and then spray some solvent through it. Then disassemble the nozzles and put them in a jar of solvent. They will be clean and ready next time. Might get more stretch even out of the cheap guns.

I use a Sharpe Titanium and Cobalt. Quality American Made gun. They will last my lifetime and the next persons lifetime. They will also set you back about 30 HF specials, so I wont press too hard.....
The average builder doesn't need a professional gun. I should have added "....and neither do I, but....)
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Last edited by JonJay : 10-04-2018 at 03:01 PM.
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  #14  
Old 10-04-2018, 03:36 PM
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wirejock wirejock is online now
 
Join Date: Oct 2005
Location: Estes Park, CO
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Default Bon Ami

Quote:
Originally Posted by PokePilot View Post
<snip>... I probably won't use any chemical etching products since I'm trying to stay away from that stuff (my process so far has been scuffing with the Scotchbrite pad, soap+water rinse, then acetone, and I got excellent results on the test pieces I sprayed). I might try to scuff up some scrap, leave it for a few days, then clean again with soap+water and acetone before spraying and see what kind of results I get. If that works well I'll probably do the same for the rest of the parts minus any
Exactly why I use a cleanser. Cuts down on exposure to chemicals including acetone.
Humor me and try Bon Ami with gray scotchbrite as your scub.
Rinse well, dry and shoot. No need for acetone.
If the water is break free on the surface, your part is clean.
Test adhesion after curing using black gorilla tape. Rub it on, leave it overnight, rip it off.
Just my $.02
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  #15  
Old 10-04-2018, 03:53 PM
greghughespdx greghughespdx is offline
 
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Location: Aurora, OR
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Shooting on aluminum where more than 24 hours time has elapsed between prep and paint will often yield results that are not what you're looking for. Heck, we had that very conversation just this week related to some work happening at the shop. Best to shoot the same day or within 12 hours of scuffing, and of course also on a well-cleaned surface.

Painting is expensive and time consuming, but *much more so* if you have to remove, re-prep and re-coat. Get the initial prep steps right and make your paint investment worthwhile. There are no real shortcuts to a solid, clean, reliable paint job and sometimes we have to do certain steps twice. Hazard of the trade.

One RV I deal with regularly was painted a few days after it was scuffed. Now the paint is peeling off the interior in large areas, including everywhere the velcro seat attach points are. The velcro is significantly stronger than the pain adhesion to the metal. Not pretty.
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  #16  
Old 10-04-2018, 04:09 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by greghughespdx View Post
One RV I deal with regularly was painted a few days after it was scuffed. Now the paint is peeling off the interior in large areas, including everywhere the velcro seat attach points are. The velcro is significantly stronger than the pain adhesion to the metal. Not pretty.
Apples to apples....epoxy primer, or the self-etching stuff, or....?
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  #17  
Old 10-04-2018, 04:39 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Default

Quote:
Originally Posted by rocketman1988 View Post
Aluminum oxidation begins immediately when in contact with oxygen.

It is, however, passivating in that the very thin layer (in the nanometer range) of aluminum oxide provides a barrier between the oxygen and the underlying aluminum.

This barrier then stops, or greatly slows, the oxidation process...
Correct. However, this layer is not strongly bonded to the aluminum. Therefore if your paint adheres to this layer, it will not be as strong as if adhered to the parent metal. This only applies once the layer is thick enough to act as a barrier.

Larry
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  #18  
Old 10-07-2018, 03:30 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by DanH View Post
Apples to apples....epoxy primer, or the self-etching stuff, or....?
Epoxy primer

Adhesion issues with self etching primer are probably much less likely to occur with a delay of a few days.

If it is a plain epoxy primer, there is no way I would go more than 24 hrs.

Is the AKZO that people commonly use, a self etching primer?
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  #19  
Old 10-07-2018, 06:36 PM
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az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
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Quote:
Originally Posted by rvbuilder2002 View Post
Epoxy primer

Adhesion issues with self etching primer are probably much less likely to occur with a delay of a few days.

If it is a plain epoxy primer, there is no way I would go more than 24 hrs.

Is the AKZO that people commonly use, a self etching primer?
They don't mention any self etching properties...

https://www.aircraftspruce.com/catal...-24735tech.pdf
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