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Primer questions

lyosha

Active Member
Hi everyone

Just starting my project and the primer question is I guess the first I have to make a decision with regards to. Having read and read this section I'm down to too many choices and a few questions that will probably govern mine.

It seems the choices are down to:
pre-treatments:
a. Do nothing and use self etching (and then have the primer scrape off from any movement)
b. Alumiprep + Alodine - this seems to add some protection but is toxic
c. PreKote - doesn't seem to add any protection but seems to prep well?
d. Stewart's Eko products pre-treatment - if using the Eko products. Perhaps less toxic.
primers:
a. Akzo - seems to be a fan favorite but also requires the most setup and might be heavy?
b. P60G2 - the stuff that Vans uses that's technically not supposed to be used to inhibit corrosion
c. Eastwood 2K AeroSpray Epoxy Primer - convenience of a spray can, but can't find any real PIREPs
d. EkoPrime - seems like not the best primer but fairly easy to use and less toxic?
e. EkoPoxy - perhaps a better corrosion inhibiting EkoPrime? The instructions indicating a 2-3 mil coating make it sound heavy though.
f. spray-can zinc phosphate primer - tempo seems no longer in production. Some company named moeller still makes it?


And now for the questions:

1. Everyone who alodines seems to use Akzo. Is that because P60G2 is not compatible with alodine or just that it's the most involved process, so the people who use Akzo are the ones that go through with it?
2. If you use alumiprep and alodine, do you still have to scuff your parts?
3. Do you prime overlapping regions of skins?
4. While I know this is subjective to how thick you spray, if you use manufacturer's guidance, how much weight would all of the above add? Are any known to be lighter than others? Roaming around I seem to see the range of weight of the same primer adding anywhere from 8 oz to 20 lbs... Did anyone do an apples-to-apples comparison?
5. Does anyone know of a proper (or improper) salt fog (or similar efficacy) test for the above?
 
Vans test

For a few decades now, Vans have been testing the SW P60G2 primer on a sample hanging outside their shop. every few years (decades) they pull off another strip and see how it is doing.
I would suggest you search that old thread and read it before deciding the SW wash primer is not suppose to be for corrosion protection. What i understood was that SW recommended this primer be top coated. Personally I think the recommendation is because it is very thin and light.

I have used the SW primer without a top coat on all the interior of the skins and all the non alcad pieces. It is between all the seams by default. (Since the insides of the skins are primed before assembly).

I have also used the same SW primer as the only prime coat for my SW Jet Flex Interior paint.

Keep it simple and the build will go faster.

Just My Humble Opinion.
 
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Question

Are you building an airplane to last 75+ years or 150?

Having primed my -10, I am not sure I would do it again. I used P60G2.

It adds a huge amount of time to the build process.

It adds cost.

It adds weight, especially if you use epoxy.

If you live in a coastal region or tie it down outside, it is definitely beneficial.

As for the long term gains; well, my 1957 C-172 had NO primer, was tied down outside for years in the midwest, and showed very little corrosion in 2010, when it was sold. So back to the first question...

I think if I did decide to prime again, I would try the alodine route...
 
P60G2

John is correct. P60G2 was not developed as a stand alone corrosion protection primer. However, given, performance price, ease of use and weight, it's pretty hard to beat.
This is the thread.
https://vansairforce.net/community/showthread.php?t=187699&highlight=P60g2

1. Everyone who alodines seems to use Akzo. Is that because P60G2 is not compatible with alodine or just that it's the most involved process, so the people who use Akzo are the ones that go through with it?
Neither. Totally different processes. Pick your "poison". If the bird is parked on the coast, maybe alodine and primer are a valid choice. Please capture all products, rinse water and dispose properly. Always wear PPE. I Alodined the exterior. It was not pleasant. I would find a commercial operation and let them do batch jobs.
2. If you use alumiprep and alodine, do you still have to scuff your parts?
Have to? I recommend it. Better results. Technically Alumiprep is an etch but it does a much better job in a scuffed surface.
3. Do you prime overlapping regions of skins?
Most get done by default but yes.
4. While I know this is subjective to how thick you spray, if you use manufacturer's guidance, how much weight would all of the above add? Are any known to be lighter than others? Roaming around I seem to see the range of weight of the same primer adding anywhere from 8 oz to 20 lbs... Did anyone do an apples-to-apples comparison?
Alodine has no weight penalty. P60G2 is lightest. 2K Epoxy is heaviest. I figured about 3lbs gained using P60G2 on my interior. I estimate 10 lbs for a 2K Epoxy. I use Kirker EnduroPrime 2K on fiberglass parts. No weight measurement, but it's definately heavier for an opaque finish ready for paint. Remember, whatever you shoot on empennage parts is pretty far behind the CoG and has significant impact.
5. Does anyone know of a proper (or improper) salt fog (or similar efficacy) test for the above?
No idea.

Another data point...P60G2 is dry to the touch in minutes. I can flip parts as soon as I finish spraying. Shoot the other side. By the time I clean up, it's hard enough to assemble.
I also used it under the interior Jet Flex.
I think there are some new Alodine products worth investigating.
 
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I recently visited a kit manufacturer that alodines EVERYTHING - they make the parts, peel off the protective plastic, then run everything through the dip tanks before packaging. Not only does everything have. A nice gold color, it gives corrosion protection between all mating parts without adding measurable thickness. Now I am sort of a non-primer guy because most unprimed spam cans have lasted for longer than a person;s lifetime. But I think that if I were thinking of a build that needed more corrosion protection than the Alclad, I’d give serious consideration to the Alodine. Sure looks nice inside!
 
Thank you all, this is insightful.

3. Do you prime overlapping regions of skins?
Most get done by default but yes.

What do you mean get done by default? If you spray only the back of one of your skins are you saying the front of the other gets covered by the primer by default at the overlap region? Or am I overthinking?
 
How it works

Thank you all, this is insightful.



What do you mean get done by default? If you spray only the back of one of your skins are you saying the front of the other gets covered by the primer by default at the overlap region? Or am I overthinking?

SW P60G2 primer works to prevent corrosion by being a sacrificial layer. SW P60G2 has quad valent chromium (hexavalent chromium is better, but after the movie "Erin Brockovich" it is not used). So as long as there is one layer of primer between the two surfaces, the corrosions prevention is taking place. One warning, the most toxic part of the SW primer is not the chromium, but the solvents used. Always wear a respirator when spaying and cleaning up wet primer. And needs to be disposed of properly; once dry, I believe the primer is much less toxic, if at all.

Edit, chromium type has been corrected in later post.
 
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So as long as there is one layer of primer between the two surfaces, the corrosions prevention is taking place.

... But isn't there a potential issue with water getting trapped between the surfaces, with only one of them primed and resistant?

Am I overthinking this?
 
Am I overthinking this?

Yep.

I didn't see what you are building, but n the RV-14 manual, Van's points out where to use primer. Generally, it's where different materials are mated together, such as steel and aluminum, etc.
 
Overlap

Thank you all, this is insightful.

What do you mean get done by default? If you spray only the back of one of your skins are you saying the front of the other gets covered by the primer by default at the overlap region? Or am I overthinking?

Maybe overthinking a little. As John mentioned, the inside of one overlap will be primed. That's adequate. You could easiely shoot the outside skin overlap area. I did. You're spraying insides anyway. It's easy enough to tape off the overlap and shoot it at the same time.
 
Actually

Maybe overthinking a little. As John mentioned, the inside of one overlap will be primed. That's adequate. You could easiely shoot the outside skin overlap area. I did. You're spraying insides anyway. It's easy enough to tape off the overlap and shoot it at the same time.

With the SW P60G2 primer, it dries so quick, that i did do this actually on the wing and fuse skins. it was easy and quick to prime the inside, flip over, mask the mating area and shot a quick prime on the overlap area.
 
Yep.

I didn't see what you are building, but n the RV-14 manual, Van's points out where to use primer. Generally, it's where different materials are mated together, such as steel and aluminum, etc.

An RV-10 on the east coast not that far from the ocean - although not as bad as Florida. I'm also far from retirement. So in the back of my mind I already made up the decision to do more than the minimum wrt. corrosion protection. Just trying to properly understand the costs/benefits.
 
I've done varying treatments throughout the plane.

Tail got mating surfaces primed with hardware store rattle can primer.
Wings got zinc chromate over everything with alumiprep/alodine
Fuselage is getting epoxy primer with Prekote.

In about 100 years, I'll let you know what falls apart first.

FWIW, the airlines typically alodine and epoxy prime everything, but they live in a much more hostile environment. Nobody is tracking their muddy boots through your RV and spilling their apple juice on the side wall. Plane isn't sitting on the ramp all night in a rain storm, buried in snow the next day followed by a heavy coating of de-ice fluid that seeps into everything.
 
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