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Will I have to re-scuff?

PokePilot

Member
I'm at a bit of a low point in my build at the moment. I spent around 3 hours scuffing and cleaning pretty much all of the ribs and spars for my HS and VS then mixing up the AKZO only for my Harbor Freight spray gun to start splattering the primer everywhere. My guess is I didn't do a good enough job cleaning the gun last time, so whatever got left in there is now hardened and is going to be really difficult to remove enough to restore the full function of the gun.

I won't be able to shoot any primer for at least a few days now. In that time, will my freshly-scuffed parts undergo enough oxidation for me to have to re-scuff everything? I have a sinking feeling the answer is yes...
 
Yes

Yes, if you want to be 100% sure and not question your decision. Will the primer stick well enough to protect the metal? Most likely.

I know just enough about chemistry to be dangerous, but I think even if some oxidation has started, and you wipe down with acetone and prime, there will not be enough oxygen left to continue the process. I'm sure if I'm wrong someone will chime in. :D
 
Aluminum Oxide

Yes, if you want to be 100% sure and not question your decision. Will the primer stick well enough to protect the metal? Most likely.

I know just enough about chemistry to be dangerous, but I think even if some oxidation has started, and you wipe down with acetone and prime, there will not be enough oxygen left to continue the process. I'm sure if I'm wrong someone will chime in. :D

Aluminum oxide begins forming immediately. However, you still have a scuffed surface which should give excellent mechanical adhesion. Akzo is pretty tough. I wouldn't scuff again but I might wash with Bon Ami right before spraying to clean any airborne contaminants. I'm no chemist and didn't stay in a hotel either.:D
 
I won't be able to shoot any primer for at least a few days now. In that time, will my freshly-scuffed parts undergo enough oxidation for me to have to re-scuff everything? I have a sinking feeling the answer is yes...

I'll say no. I don't think a few days will make any difference at all. The skins and ribs are alclad, a surface coating of 1100. Oxidation is very slow. The clean and scuff process is more about, well, cleaning and scuffing.
 
if you have any doubt

Wash the parts with Ospho (mixed about 1-3 with distilled water) and rinse. Easy process, and you KNOW it's good to go.
 
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Thank you all for your input. 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 additional scuffing.

I just ordered a Critter spray gun which uses an airbrush-style atomization that separates the paint and air components to make cleanup easier. I hope it gets here soon – having a pile of parts ready for priming that I can't do anything about yet is making me restless! I'll test it a couple of times beforehand on some scrap, and hopefully I'll be able to avoid messing up this gun too :eek:
 
mixing up the AKZO

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.
 
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Something to think about: I took a scrap rib and I did zero prep and sprayed with akzo. I did a test where I scratched a pattern right through the paint into the metal then applied some super sticky ZIP flashing tape to the area then ripped it off. The AKZO stayed on. I'm not saying you don't have to prep your parts, I did this test to ease some of the paranoia caused by reading all the prep and primer war stuff out there.
 
...My guess is I didn't do a good enough job cleaning the gun last time, so whatever got left in there is now hardened and is going to be really difficult to remove enough to restore the full function of the gun...

BTW, in my shop we generally keep two or three brand new HF spray guns on the shelf and ready to go. We usually break out a new one for any big spray (in-mold primer for wings or fuselage), when the consequences of failure are greatest. After that, the guns get relegated to small part sprays. The longest I've had one last is about fifteen uses.

They can be disassembled and cleaned, but at $16 a pop ($10 with coupon when on sale), the time spent doing so just doesn't pencil out.

--Bob K.
 
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...
 
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.
 
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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Bon Ami

<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
 
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.
 
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....?
 
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
 
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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