Paint expert on Primer failure ...

Hi all,

It appears I?ve had a major primer failure and desperately need some advise please.

In brief - the Alclad parts where put through a very controlled (isolated and timed) process through a Alumiprep bath for 3 minutes, then directly into a water bath for neutralising (not allowing chemical to dry on surface), then directly into an Alodine bath for 2 minutes (2 - 3 seconds exposure to atmosphere in between dunking), then directly back into water bath for neutralising (again not allowing chemical to dry on surface).

The parts were left hanging to cure for over a week and were handled with gloves to eliminate any contamination of oils from hands. All precautions where taken to keep the parts pristine.

The parts where then sprayed with Shirwin-Williams primer ... CM0483787 primer, CM0120787 adduct, CM0110787 reducer - with precise mixing and induction of 15 minute as per instruction. These primed parts where then left to cure for seven days before handling.

RESULT: During the riveting process, cracking and flaking of the primer appeared around rivets (please see photobucket links below). Interestingly, the primer was coming off with the Alodine treatment attached leaving just the bear aluminium. I then thought that perhaps there was an issue (failure) with the Alumiprep and Alodine treatment ... so proceeded to follow exactly the same process on two separate test samples. After full curing, i bent, deformed and manipulated these test sample to see if i could fail the coating - but not a single fault appeared until the Aluminium reached stress levels. Hence, this leads me to believe the primer may be the cause - as it appears to be brittle.

That said, it seems the primer is bonding to the Alodine extremely well, however the primer seems brittle and is departing with the Alodine coating ... i'm puzzled how the primer is pulling the Alodine off the Alclad?

Can someone can please shed some light on this dilemma.

Cheers,
Matt

http://i1188.photobucket.com/albums/z401/matt-ally/P1070292.jpg
http://i1188.photobucket.com/albums/z401/matt-ally/P1070288.jpg
http://i1188.photobucket.com/albums/z401/matt-ally/P1070291.jpg

Primer

I am no paint expert so let's get that out of the way.

1. Are you priming before riveting if so why?. I cannot imagine how you can keep the primer from cracking with a rivet swelling around the hole.

2. When I acid etched my "completed parts/aircraft" I scuffed with a scotch brite to provide a bonding surface before alodine however this may be different depending on the etch product you use.

3. What was the humidity the day you shot the primer.

4. Give Grady a call at is shop at 52F and he will have your answers.

Pat

Pat Stewart said:

I am no paint expert so let's get that out of the way.

1. Are you priming before riveting if so why?. I cannot imagine how you can keep the primer from cracking with a rivet swelling around the hole.

.....Pat

Click to expand...

You certainly can if you use the AKZO primer. You can even dimple after priming with no primer cracking....

If you prime after riveting you do not get primer inbetween the mating surfaces which is where they are most needed - think moisture penetration.

I would add Scotchbriting to the Alumiprep step. Yeah, Alumiprep etches, but you want to be really sure the primer has a good mechanical bite.

Also, you didn't mention if you cleaned the parts with detergent or similar degreaser prior to Alumiprep. You need to make sure you clean any oil off before Alumiprep. And use don't use any rags or towels that have been in your (or anyone elses) washer/dryer. Silicone is found in dryer sheets and softeners. Paper towels are a safe bet.

I agree with Mike W. I'm using PPG Super Koropon and their application guide has a lot more details than you're reporting:

1. Wet abrade with a fine Scotch-Brite™ pad and water.
2. Solvent clean with Desoclean® 110 cleaner and wipe dry.
3. Use an alkaline cleaner, rinse with warm water, and make sure no residue remains.
4. Acid etch with a mild acid brightener. Agitate the brightener with Scotch-Brite™ pads. Note: Mix the brightener according to the manufacturer’s instructions.
5. Water wash to neutralize the acid brightener. Next observe the surface for water breaks. If a water break occurs before 30 seconds, repeat steps 4 and 5. Also check pH of run off water.
6. Apply the chromate conversion treatment.
7. Rinse with water.
8. Check for water break-free surface.
9. Allow the surface to dry completely.
10. Apply Super Koropon® primer within 24 hours of applying the chromate conversion treatment.

Perhaps your process includes all of these steps but you didn't describe them (or perhaps they're not called for). Additionally, your primer coating looks awfully thick. Ours are merely (or nearly) translucent.

Finally, alas, I am not an expert; I'm just reporting the process that's working for me.

- John

Primer flake

Matt,

I Had the same problem with SW product. I see that you are using a MIL spec product. It is much more expensive than the SW automotive etch primer that I am using but I think it is safe to say that SW products do not mix with other products! AT ALL...

Here was my experience with some pics.. I started out using PPG. I used their etch, alodine and a quart of their epoxy primer. I had a short past in the auto body repair world in the eighties and PPG was pretty much all we used. Fast forward to 2009 and all the products have changed. No more lacquer primers, fillers, etc. I thought that the PPG process was going to be long and labourious so I started to look around and found the SW etch primer. There is no surface prep other than roughing up the surface with 400G sand paper or red scotch-brite pads. Here is a link to the product. http://www.sherwin-automotive.com/products/show_product.cfm?product=E2G970 I was rolling along just fine until I decided to finish using some of the PPG etch/alodine instead of throwing it away. Big mistake. Here is a link to the thread on what happened..http://www.vansairforce.com/community/showthread.php?t=58291

Lesson learned...Don't mix products. It could cause unintended consequences...I have used nothing but the SW E2G970 followed my a high build primer for block sanding and final prep for painting, P30A SpectraPrime. SW says any of their topcoat products will work just fine using this process.

Good luck and I hope that helps!

Silicone...bad

fl-mike said:

...<SNIP>...And use don't use any rags or towels that have been in your (or anyone elses) washer/dryer. Silicone is found in dryer sheets and softeners...<SNIP>...

Click to expand...

Yes, yes...silicone is an "evil" contaminant in the space shuttle solid rocket motor business where adhesive properties are so important. I'm still convinced I messed up the pro-sealing of my first rudder trailing edge on my 7 due to silicone contaminated rags from our house.

Primer Failure

I followed the Alumiprep/Alodine prep steps you described (without the scotchbrite scuff) but used Super Korapon as one of the other posters did. Have had good results on empennage, wings and fuselage. Paint is very hard to scratch but still flexible. Have noted some flaking when I did dimpling after priming.

Not a paint expert, but you might consider getting your water analyzed to see if there is anything in it that might affect the bond. I would report this to Henkel (alumiprep and alodine) and get their advice as well.

More on my prep ...

Hi Guys,

Firstly - my sincere thanks for the detailed responses ... much appreciated.

Just to clarify, i did give the surfaces a thorough scotch-brite pad make over before the Alumiprep / Alodine treatment. I also wiped the parts down with MEK prior to the treatment to remove any remaining contaminants ... could this have caused the problem?

After reading your responses, i've also realised that i used some freshly washed rags to do the cleaning - perhaps this was another issue ... i think i'll go with the paper towel advise in the future.

My other question ... seeing i will need to start again and paint strip the parts, will the paint stripper remove the Alodine ... or is this something that will only become evident when i go through the motions?

Gil : are you able to provide me the AKZO product numbers of the product you recommend ... i'm based in Australia and this stuff is virtually impossible to find.

Cheers,

Matt

I used scotchbrite pads and dish soap to wash and scuff all my parts then primed with SW P-60 etch primer. Never had any problems. You could be applying your primer a little heavy which might be causing some of your problems. Just a guess though. Hope you get it resolved. I know how frustrating that can be.

The other comment I meant to make is that perhaps a 1 week cure before riveting is excessive. I would try to rivet shortly after the material application guide says that it's okay to do so while the paint is still somewhat soft.

- John