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Akzo 463-12-8 on external surfaces.

M

Mike H

Well Known Member
I have read that the Akzo primer is primarily used on internal surfaces and must be heavily scuffed or sanded prior to top coating. My question is whether any one besides me thinks it is a good idea to epoxy prime the exterior of thier aircraft?

I work for a large aircraft manufacturer who epoxy primes every square inch of the entire aircraft using a similar Skydrol and solvent resistant epoxy primer that made by PPG Deft. This PPG primer is thicker, heavier and does not lay down as smooth as the Akzo, but it is used to seal and protect the external surfaces prior to the aircraft being outfitted and painted with a customer's specified paint scheme. The painters simply scuff sand the primer than apply a primer coat that is compatible with the top coat.

The are several reasons why I am considering priming both sides, the primary concearns are as follows:
1: S.E. Georgia is HUMID! and even Alclad aluminum will corrode inside the hangar or garage.

2: I have extremely corrosive skin oil and can rust steel tools or corrode bare aluminum in a matter of hours.

3: The exterior of the aircraft will be protected During the time between completion/first flight untill I paint it, or have it painted.

4: Epoxy primer has a tendancy to fill small voids such as areas around rivet heads and countersinks, which makes the final finish look a bit nicer.

So every one has an opinion...so lets hear them!
 
primer

No reason not to, but Savannah is not worse than many places for corrosion.
Gulfstream does it to hide the poor skin quality, ever see a Gulfstream delivered with bare aluminum ala American Airlines Boeing? There's a reason for that.
I never had corrosion issues with my Cessna that had a unprimed interior when I lived there and parked at KSAV.
 
Paul, I have to disagree with the assesment of "poor skin quality" and the reasoning why some heavy airliners are polished and not painted. Boeing heavys use a skin that is 3-4 times thicker than most pressurized business jets. These thicker skins also use far fewer fasteners and do not flex as much as thinner skins with many times more rivets, hence they do not look as smooth as an airliner. Also some airlines polish instead of paint for weight and cost reasons, not for showing off "superior workmanship".

Yes there are worse places than Savannah for corrosion, but it is still a concearn in all of the S.E. and other coastal areas.
 
One consideration is if you plan to final paint the plane or hire it out. If a shop paints the plane they will likely strip any existing paint/primer off since they have to guarantee their work and have no idea of the quality of the existing coating. So, in this case you could go with a less expensive temporary protective primer. If you paint it, you will have to scuff any primer to ensure adhesion of the top coat as you will be way outside the primer top-coating time window. Flying the plane in primer isn't the best idea since you will get oil soaked areas leading to topcoat adhesion issues.

If you can build the whole plane in a month, don't bother priming the exterior. If it will take longer, the key to preventing corrosion in humid environments is to keep the parts clean and dry. Dirt particles hold moisture against the metal and start corrosion cells. (and take the plastic off!) So, I prime everything or store parts in a climate controlled clean area (the spare bedroom!). Hangars/garages/sheds are a bad place to store bare metal in my (and your) neck of the woods.
 
skns

Boeing skins are .080, Douglas .063. I know about Gulfstream, I worked on the floor and in tech pubs for years. Never seen a Boeing scrapped for corrosion on a ten thousand hour airplane like the Gs are. Worked at American, the skins are not polished, just bare aluminum.
 
fl-mike said:
..... Flying the plane in primer isn't the best idea since you will get oil soaked areas leading to topcoat adhesion issues.

.....
Click to expand...

Isn't this what most composite planes do, fly in primer before finish paint?
 
composite

I think composite guys fly with the gel coat before painting. What ever happened to using carbon black under the primer?
 
One consideration is if you plan to final paint the plane or hire it out. If a shop paints the plane they will likely strip any existing paint/primer off since they have to guarantee their work and have no idea of the quality of the existing coating.
Click to expand...

You may have a good point there, I will check with some painters and get their opinion.

Flying the plane in primer isn't the best idea since you will get oil soaked areas leading to topcoat adhesion issues.
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Remember this is a solvent and Skydrol resistant epoxy primer that seals the coverage area. This type of primer would actually help preclude the adhesion issues you are referring to. If it were regular non solvent resistant primer I would agree with that statement.

Isn't this what most composite planes do, fly in primer before finish paint?
Click to expand...

Many composite planes do fly with a primer finish, or bare gelcoat depending on the type of kit and parts finish. It is not easy to get oil soaked composite to take paint, been there, done it.
 
I talked to several of the painters at work regarding priming the entire external surface with Akzo 463-12-8. Everyone I spoke with highly recommended its use on external surfaces to prevent corrosion and give the top coat primer good adhesion. It was also recommended to prime over the rivet rows after assembly to seal out contaminants and oil. They said they would not strip off the epoxy primer prior to top coat paint unless the primer was solvent or oil damaged and starting to peel, this will not be an issue since there is no Skydrol in an RV. Prep for final paint should consist of cleaning the external surfaces, light sanding or scuffing the primer with sand paper or scotchbrite and solvent wiping to remove any contaminants prior to top coat primer application.
 
Good info, Mike. You really got me thinking with this thread. I really need to move my tailcone to the hangar, but really don't want it sitting out there unprotected. Any word on what someone mentioned earlier I believe - about it causing problems if getting professionally painted? Not sure if you're planning on painting yourself - I am NOT:D. I would hate for it to cause more problems down the road. Guess I could shoot an email off to several of the often used paint shops and ask.

The bottom line is that Akzo is really tough stuff, and I'd feel much better being able to prime the external surfaces prior to storing at KLHW.
 
Jon, I have not decided if I will have one of the painters from work spray it, or if I will take to a paint shop. I have not contacted any paint shops that do small piston aircraft and asked if they would require that the primer be stripped off.

All of the aircraft we build at work are externally primed with a similar solvent resistant primer. There is a period of at least six months between final assembly and test flights, and the application of customer specified paint. A month or two of this time is outside on the ramp or flying.

I have been told that the primer does not get chemically stripped for the initial paint job application. It gets lightly sanded or scuffed with scotchbrite and the primer that is used with the top coat paint is then applied. The painters said that the Akzo primer will provide good adhesion for top coats if heavily scuffed.

I will talk to some of the guys in the paint hangar next week and confirm that the initial coat of primer does not get stripped. I do know for a fact if the airplane is getting repainted that it gets chemically stripped all the way down.
 
I talked to on of the crew leads that runs a paint crew in on of our paint hangars. He said that he likes the Akzo primers much better that the PPG/DEFT products that we normally use (some of other facilities use the Akzo instead of the PPG). He also reccomended priming the entire exterior surface with Akzo 463-12-8. I also confirmed that new aircraft that are exterior primed with solvent resistant epoxy are not chemically stripped, but scuff sanded, prior to top coat primer/top coat color application. Prep for top coat consist of washing the aircraft with detergent to remove grease/oil/dirt, followed by wet sanding the Akzo with 600 grit paper untill the primer is water break free, then solvent wipe just prior to top coat compatible primer application.

Having confirmed this I will be priming all exterior surfaces with Akzo 463-12-8. Seems to be a proven process with several OEMs, so I don't see how I could go wrong. In a couple of years from now I will know for sure ;)
 
Mike H said:
I talked to on of the crew leads that runs a paint crew in on of our paint hangars. He said that he likes the Akzo primers much better that the PPG/DEFT products that we normally use (some of other facilities use the Akzo instead of the PPG). He also reccomended priming the entire exterior surface with Akzo 463-12-8. I also confirmed that new aircraft that are exterior primed with solvent resistant epoxy are not chemically stripped, but scuff sanded, prior to top coat primer/top coat color application. Prep for top coat consist of washing the aircraft with detergent to remove grease/oil/dirt, followed by wet sanding the Akzo with 600 grit paper untill the primer is water break free, then solvent wipe just prior to top coat compatible primer application.

Having confirmed this I will be priming all exterior surfaces with Akzo 463-12-8. Seems to be a proven process with several OEMs, so I don't see how I could go wrong. In a couple of years from now I will know for sure ;)
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Can you ask the crew lead the same questions, but with the use of a Mil Spec primer to MIL-P-23377?

Lots of manufacturers make this primer, which is described as -

This specification covers the requirements for two-component, epoxy, chemical and solvent-resistant primer coatings formulated primarily for application by various spray techniques. They shall be compatible with epoxy and polyurethane topcoats.

The Akzo product is similar, but made to a proprietary M-D, now Boeing, spec.
 
I will ask him when I see him again. The other solvent resistant primer we use meets the following specs: BMS 10-11AB TYPE I CLASS A GRADE E
BAMS 565-001C GRADE B CATEGORY 2 TYPE 1 RMS118H TYPE I CLASS L and M. I don't know if it meets MIL-P-23377.
 
Mike H said:
I will ask him when I see him again. The other solvent resistant primer we use meets the following specs: BMS 10-11AB TYPE I CLASS A GRADE E
BAMS 565-001C GRADE B CATEGORY 2 TYPE 1 RMS118H TYPE I CLASS L and M. I don't know if it meets MIL-P-23377.
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No it doesn't meet the 23377spec. I believe that is a water reducible primer, not a solvent one.
 
Gill, He said the products we use do not list MIL-P-23377 compliance. He said it should be similar since all solvent resistant primers are sealer type primers.

I did look at the spec document for MIL-P-23377. It has instructions for top coating.

If a topcoat is not used, the primer coatings shall be allowed to air dry for not less than 14 days,
or air dry for not less than one hour followed by 24 hours at 65.5 ? 3 ?C (150 ? 5 ?F) prior to
testing. If a topcoat is required, the primer coatings shall be air-dried for 5 hours and then coated
with a polyurethane coating conforming to MIL-PRF-85285 in accordance with 4.4.2.
4.4.2 Application of topcoat. When a topcoat is required by the test method, mix
polyurethane coating conforming to MIL-PRF-85285 (untinted gloss white conforming to
FED-STD-595, color number 17925) adding thinner, if required, and allow it to stand 30 minutes
prior to application. Apply the coating to a total dry-film thickness of 43 to 58 μm
(1.7 to 2.3 mils). If applied in two coats, allow the first coat to air dry for 60 minutes prior to
application of the second coat. After application of the topcoat to the required thickness and
prior to testing, allow the coating to air dry for not less than 14 days or allow the coating to air
dry for one hour followed by 24 hours at 65.5 ? 3 ?C (150 ? 5 ?F).
 
Mike H said:
I talked to on of the crew leads that runs a paint crew in on of our paint hangars. He said that he likes the Akzo primers much better that the PPG/DEFT products that we normally use (some of other facilities use the Akzo instead of the PPG). He also reccomended priming the entire exterior surface with Akzo 463-12-8. I also confirmed that new aircraft that are exterior primed with solvent resistant epoxy are not chemically stripped, but scuff sanded, prior to top coat primer/top coat color application. Prep for top coat consist of washing the aircraft with detergent to remove grease/oil/dirt, followed by wet sanding the Akzo with 600 grit paper untill the primer is water break free, then solvent wipe just prior to top coat compatible primer application.

Having confirmed this I will be priming all exterior surfaces with Akzo 463-12-8. Seems to be a proven process with several OEMs, so I don't see how I could go wrong. In a couple of years from now I will know for sure ;)
Click to expand...

Thanks for tracking this down, Mike! I think I'll follow suit with the exterior priming. I'll feel much better with parts sitting in the hangar that way.
 
Mike H said:
I talked to on of the crew leads that runs a paint crew in on of our paint hangars. He said that he likes the Akzo primers much better that the PPG/DEFT products that we normally use (some of other facilities use the Akzo instead of the PPG). He also reccomended priming the entire exterior surface with Akzo 463-12-8. I also confirmed that new aircraft that are exterior primed with solvent resistant epoxy are not chemically stripped, but scuff sanded, prior to top coat primer/top coat color application. Prep for top coat consist of washing the aircraft with detergent to remove grease/oil/dirt, followed by wet sanding the Akzo with 600 grit paper untill the primer is water break free, then solvent wipe just prior to top coat compatible primer application.

Having confirmed this I will be priming all exterior surfaces with Akzo 463-12-8. Seems to be a proven process with several OEMs, so I don't see how I could go wrong. In a couple of years from now I will know for sure ;)
Click to expand...

Mike, what is the surface preparation recommendation for this primer? Alumiprep, alodine, wash primer, CR? I looked at the AN data sheet and it had no surface prep recommendation/requirements.
 
Scuff with maroon scotchbrite, solvent wipe (acetone) apply the Akzo primer. Some builders use acid etch after scuffing with scotchbrite, but most report that there is no difference in adhesion using the etching solution or not using it.

The painters at work concurred and said since I will be prepping and priming clean Alclad parts to skip the acid etch since they thought it would be a waste of time. They said if I was priming non clad aluminum, or Alclad parts that had some surface corrosion that I should definitely use etching solution after scuffing to clean the aluminum prior to primer application.

Hope this helps.
 
Mike H said:
Scuff with maroon scotchbrite, solvent wipe (acetone) apply the Akzo primer. Some builders use acid etch after scuffing with scotchbrite, but most report that there is no difference in adhesion using the etching solution or not using it.

The painters at work concurred and said since I will be prepping and priming clean Alclad parts to skip the acid etch since they thought it would be a waste of time. They said if I was priming non clad aluminum, or Alclad parts that had some surface corrosion that I should definitely use etching solution after scuffing to clean the aluminum prior to primer application.

Hope this helps.
Click to expand...

Do they use a chemical conversion coating (aka alodine) on the big planes they paint?
 
Gil, the short answer is yes. All of the skins and detail parts are alodined and primed with PPG/DEFT primer prior to assembly. When they scuff sand the exterior prior to top coat application, they will alodine any areas that go all the way through the solvent resistant primer and down to bare aluminum. There are two reasons they sand the initial solvent resistant primer coating, the frirst is that the PPG/DEFT primer is a high solids paint and it goes on very thick, the second reason is they are held to a 5 mil max paint application thickness.

For our application I don't see the need to "sand off" any of the Akzo primer since the Akzo primer lays on very thin and uniform. I plan to wet sand the Akzo with 600 grit until it is water break free, solvent wipe and apply the primer to be used with the top coat paint.
 
Corrosion protection for vinyl wrapped aircraft may be another good reason to prime the external surfaces with Akzo.
 
After evaluating a number of primers, I primed my -4 inside and out with Deft water-reducible epoxy primer. I flew the plane in primer for several weeks and then brought it to the paint shop. My painter was not familiar with this Deft product and decided to scuff-sand the surface and re-prime (with his own favorite primer) prior to top coating. The topcoat has lasted well, though I probably paid some level of weight penalty for the two coats of primer.

I etched, Alodined, and primed everything prior to assembly and enjoy the peace of mind of having a well-protected aircraft. For the wings and fselage, I batched parts and brought them to local platers for etch and Alodine. This saved much time for modest cost. For the wing skins, I used a plater that painted as well. Generally, I provided the Deft paint, but sometimes I had them use the paint they sprayed for their "real" aircraft customers.

Good luck,
 
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