SW GBP-988 over Alodine treatment?

I was wondering if anyone has had personal experience applying GBP-988 spray can primer over Al treated with alodine?

SW tech support says not recommended. however, someone from a local paint store says he has personally had no issues with using a SEM primer over alodine.

I was initially only planning on using the 988 for priming. however, on some VS ribs, I overdid it with the scotchbrite and wore through the alcad layer in spots. Next time, i won't bother trying to debur every tight spot; however, I did learn how thin the alcad layer is.

At one end of the spectrum, instead of leaving these spots, i thought I might try to alodine treat these spots where i wore thru the alcad (maybe using the alodine pen?).

At the other end of the spectrum, i thought why not just alodine treat an entire part, so the alodine treats all those scratches and machined areas. From what I have read, alodine is not very effective on untouched alcad, anyway. This way, every surface area has the outer primer protection as well as an inner alcad or alodine protection layer as well, even at machined edges and holes.

Thanks for the input,
Jae

988 is an etching primer which technically requires a bare aluminum surface to do its thing. 988 is for spot priming and the PE990 is for large applications and is an epoxy two part primer.

I can't say that what you're doing is going to create problems. I've used 988 over anodized parts and it seems to work fine and stick to the surface well. Technically if you want to comply with the manufacturers instructions, you should not alodine the part and use 988 over bare aluminum. Or, you can alodine and use PE990. It's more of a hassle to apply because you have to load it up in a spray gun.

BTW, I'm currently painting my Rocket with SW paints so I'm getting really familiar with their paint systems. Here's a link to all their spec sheets:

http://www.sherwin-automotive.com/media/pds/swpds.pdf

jchang10 said:

SW tech support says not recommended.

Click to expand...

Do you or your paint sales guy know something the manufacturer doesn't? If SW didn't have reason to say "not recommended", they wouldn't say it.

Test Results

Well, i was finally able to do my own tests. I was fortunately able to find local sources for both alumiprep, alodine, and 988.

My tests confirmed what others have said and what i think makes sense. I did these tests, in order of strength of adhesion of the primer.

A. acetone wash, light scuff, 988 - 2 days of curing

the rest was after only 2 hours of curing

B. alumiprep, light scuff, alodine, 988

C. alumiprep, medium scuff, alodine, 988

D. alumiprep, rough scuff, alodine, 988

#D gave the best adhesion.

#A is what is recommended on the label. However, I felt it gave good ahesion, but the weakest adhesion.

More scuffing improves adhesion, which makes sense to improve mechanical bonding.

The main test was to see what effect alodine gave. Alodine certainly seems to improve bonding, even after allowing the primer over alodine to dry for only 2 hours; whereas, sample #A had cured for several days.

It is also more comforting to see the gold hue instead of bright silver after scratching epoxy off.

That is my 2c and hope that helps someone else.

Jae

SW Response

Brad... actually, the label on the can says "Ideally, primer is applied to bare metal."

I know the SW tech said the same thing, quoting the company line, but not from personal experience. Several people I had asked about applying 988 over alodine have all said, no problem.

I just had to verify it myself. I could probably apply a non self-etch primer, but i like the 988 and with enough positive results with 988, i figure why change, for now.

jae

Jae,

Now do a corrosion resistance test on the 988. I think you will find it has no protection without topcoating it.

Tracy.

Jae--

Have you seen the latest issue of RVator? They included an article about priming that I think is the strongest statement Van's has made to date (that I've seen) about the need, or lack thereof, to prime to mil-spec. It included some of the ideas about scuffing/not scuffing, priming, not priming that you ask about, but basically seemed to suggest that (as with their quickbuilds) a light coat of primer by itself (without topcoat) is more than sufficient for our purposes and that much more is overkill. I'm definitely not trying to start a primer war, and do a little more priming than that myself, but for new builders trying to decide, I don't think you need to lose any sleep over this issue, even though we all do! Good luck.

I just read the article in Rvator #6 and after 3-1/2 years the aluminum was still nice and shiny under the SW P-60 primer. To me that proves it does help protect bare aluminum. I'm using the same on my RV-9A that Van's uses (SW-P60). My opinion (which is pretty much worthless) is it will never benefit the original builder, owner, but if you get a warm fuzzy knowing that someone flying your pride and joy long after you're dead and gone is protected from corrosion then grab that spray gun and knock yourself out. That said, I would still prime anything that has had filing, deburring or not alclad. I did it only on the chance it will help resale value if I ever decide to sell it. I can see my self someday having to sell the RV-9A and building an RV-12 because of medical issues. Not anytime soon I hope! I still buy semi green bananas.

I will be looking for the issue

Great timing, i will be looking for that issue to arrive, hopefully, soon!

Jae

Local Source for Alodine?

Jae,

Can you let me know where the local source you found for alodine was?

Thanks,
Scott

Local Auto Paint store

tx_jayhawk said:

Jae,

Can you let me know where the local source you found for alodine was?

Thanks,
Scott

Click to expand...

Our local high end DuPont auto paint store (FinishMasters) stocks alodine... try a good auto paint store, it should be easy enough to get.

DuPont calls it 226S Conversion Coating.

Note that alodine is not actually a protective layer, it is a sacrificial coating that will migrate into scratches and prevent corrosion. That's why a full Mil-Spec system requires alodine covered with a hard epoxy primer... if the primer is scratched, then the alodine does it's thing....

gil A