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Maximum scuff to primer time

Blain

Blain

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Any thread that has primer in it is bound to stir up a hornets nest but here goes, what is the maximum time between the scuff to shooting epoxy primer? I know aluminum starts oxidizing immediately. But what is practical? My process is slow so I could be a couple of weeks to get primer on it. Since it’s nearly summer here in Northern California humidity isn’t a big concern.
B
 
I try to keep it under a four hours. Most folks that i know in the business suggest 2-4 hours from scuff to application on aluminum. Humidity is not required for the oxidation to occur unlike steel. No way I would go a week from scuffing. Just asking for trouble IMO. You want the primer adhering to the metal, not the oxidation layer.
 
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Alodine your aluminum immediately after your scuff and you'll have much more of a time buffer before priming. Although it certainly isn't impervious to the elements, the chromate conversion provides at least a layer of protection against oxidation before you commit to the HVLP.
 
My rule of thumb has always been to prime within 24 hours of the metal being washed, etched, and alodined. Since I don’t work weekends, I don’t wash on fridays.
 
Scott Chastain said:
Alodine your aluminum immediately after your scuff and you'll have much more of a time buffer before priming. Although it certainly isn't impervious to the elements, the chromate conversion provides at least a layer of protection against oxidation before you commit to the HVLP.
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+1

After the conversion process, the oxidation layer stops forming, so have plenty of time before spraying.
 
lr172 said:
I try to keep it under a four hours. Most folks that i know in the business suggest 2-4 hours from scuff to application on aluminum. Humidity is not required for the oxidation to occur unlike steel. No way I would go a week from scuffing. Just asking for trouble IMO. You want the primer adhering to the metal, not the oxidation layer.
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2-4 hours. Exactly.
Here's another process. FWIW.
Scuff and wash at the same time.
Scrub with Bon Ami cleanser and maroon scotchbrite pads. Rinse well. Dry with clean shop paper towels.
Set up paint while they dry completely.
 
I'd look at the TDS for whatever prep you're using. It'll tell you the allowable time between the prep stage and top coats. I think the general guidance is "as little as possible". For example, I use PreKoat and scuff concurrently to applying PreKoat - it recommends primer on top within 24 hours.

I prime as soon as the rinse after PreKoat is dry, and you're even allowed to use a forced air dryer (aka hair dryer, etc) to speed that up if needed.
 
Well, was I lucky, dumb, or?
I scuffed many days prior to (epoxy) primer. 320 sandpaper.

Cleaning all that scuffing residue is important. Get the dust off and gone! Not into the air. Primed within a window of something like 2-4 hours of final clean with Southern Polyurethanes (SPI) Solvent Wax & Grease Remover.

I'm not having adhesion issues. But maybe chalk that up to SPI epoxy primer.
 
My understanding is that most oxide formation happens in the first few minutes after scuffing (see generally https://pubs.acs.org/doi/10.1021/acsami.7b17224), and therefore, whether you wait 4 hours or 24 hours to prime shouldn't make much of a difference if oxidation is the concern. Perhaps the bigger concern is that the longer something sits around the more likely it is to be contaminated with finger prints, oils, and other stuff that can affect adhesion or the finish. That's why I always clean my parts right before priming and then let them sit in the paint booth to dry before spraying. I've definitely let some parts sit for days after scuffing and before priming and I've never seen any difference in adhesion, but maybe I got lucky too.
 
I alodined parts yesterday. I won't have a chance to prime for another week. Reading up on this through these forums, it seems like I can wipe clean with Acetone before priming and spray. The parts are in a climate controlled garage with relatively low humidity(40%). Does this sound good?
 
flymore said:
I alodined parts yesterday. I won't have a chance to prime for another week. Reading up on this through these forums, it seems like I can wipe clean with Acetone before priming and spray. The parts are in a climate controlled garage with relatively low humidity(40%). Does this sound good?
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Yep. Alodined surface is stable for quite a while.
 
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