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Primer on Eventually Painted Surfaces

FlyerJumper

Well Known Member
This question is mainly directed at anyone using the AKZO primer... Are you guys using the AKZO primer on surfaces that will be visible in the end and probably painted (rear spars of the vertical stabilizer and horizontal stabilizer for example) Its my understanding that paint doesn't adhere very well to the AKZO, and since I do plan to eventually paint this plane I started wondering if it might save me a considerable headache come paint time if I started planning for it now.

Any suggestions greatly appreciated.
 
FlyerJumper said:
Its my understanding that paint doesn't adhere very well to the AKZO
The whole purpose of most primers is as an undercoat to a top coat, so I would question your understanding. The data sheet is available on line, after a little searching IIRC, it will tell you how to apply paint over the primer. Often, if you don't overpaint quickly, you must rough up to ensure a good key. I don't think this is a huge problem - how many RVs have you seen with paint falling off the VS or HS spar? I can't recall seeing one.

I don't know how the 10 is designed, but on most other RVs the VS and HS spar has a stiffener that is not alclad and must be primed to avoid corrosion. Corrosion is a real threat while you build the rest of the airplane, as well as once you are flying. So, yes, prime the spar to avoid having to build another VS and HS just before you fly.

Having said that, I haven't primed the outside of any skin as you really should use a primer that is compatible with your top coat, as most manufacturers supply a paint 'system' and recommend using their products throughout. Its difficult to tell if this is manufacturers trying to make sure they sell more paint, or good advice, most people are unwilling to take the risk! So any area you have already primed will have to be primed again with a primer that it compatible with your color coat - as I suspect you don't know what type of paint you will eventually use. That's no big deal for the back of the HS or VS spar and adds very little weight. But if you primed the whole of the outside of the emp, then you might be able to measure the additional weight. Its should not be a problem from the compatibility perspective, AKZO is an epoxy paint and once cured shouldn't react with very much, but it will add weight and take more time.

Pete
 
My 2 cents (and I did use AKZO):
Limit how much AKZO you use on exterior surfaces. And I'm not talking about skins...I'm talking about exterior facing portions of the HS and VS spars, rear wing spars, flap brace, elevator end ribs, etc. You or your paint shop will probably have to sand it clean (to some extent) before shooting primer for paint. AKZO is stubborn stuff and is not easily removed with solvents (although your paint shop may have some hard core industrial stuff to make it easier...but do you want that oozing into mating areas?).

Two things happening here...one is that you're right, AKZO is not designed to take a top coat, and two is that there will be months (years?) between the time when you shoot it on the earliest parts and when you're ready to paint.

Imho AKZO kicks butt as a primer, but it's an "interior" primer (I think that's the actual Akzo-Nobel product name.
 
dan said:
Two things happening here...one is that you're right, AKZO is not designed to take a top coat, and two is that there will be months (years?) between the time when you shoot it on the earliest parts and when you're ready to paint.
Dan,

If you're talking AKZO 436-12-8 primer from Spruce, I disgaree with your statements. There is nothing on the data sheet to say its not designed to be over coated. It does say apply the top coat within 48 hours. There is no advice on what to do after that. The only "name" on my tin is the ref no. You're right that it is a very good primer and highly resistant to pretty much anything our aeroplanes can throw at it. I think we should be careful not to give products an undeserved reputation.

Pete
 
Dirty primer

In my experience you need to paint the primer with in a very small window after priming. Time in hours but no more than days. Clearly old primer is "dirty" and contaminated. To get it back you basically will sand most if not all of the primer off and prime again. This is generic painting 101. So don't prime what you plan on painting until you are ready to paint. Whether you paint as you go or do it all later is your choice.

Ask your local auto paint store that sells this product. I find if you ask they will give you the detailed manufactures procedures and processes. I am a paint dummy in that I follow the manufactures instructions as close as possible.
 
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Interesting. I don't have any cans of it anymore but I thought they said "interior primer" on 'em. I could be mistaken!
 
All the language on the can says that it is fluid resistant, which suggests to me that it is designed as internal protection against oil, hydraulic fluid, fuel, etc. Dan is right that paint doesn't stick to cured akzo very well unless you scuff the heck out of it (guess how I know). It is a sealer and very tough so I wouldn't get too hung up on this business about it being dirty or contaminated. Just give it a good wipe down with the carcinogen of your own choosing, scuff, clean again, and all will be fine.
 
The data sheet....

Dan is correct... the ACTUAL data sheet is here....

http://www.anac.com/products/DataSheets/463-12-8.pdf

and it is described as "463-12-8 Interior Fluid Resistant Epoxy Primer" to a Boeing Long Beach (was McDonald-Douglas) specification.

We have several early RV builders from the CA South Bay area to thank for this product... they used it at work, probably 'liberated' some... :)... and then persuaded Aircraft Spruce to stock it.

An early example is the Oshkosh award winning RV-6A of Steve Barnard. Steve did use this primer in his cockpit area (I believe he was a McDonald-Douglas sheet metal worker), and just scuffed it with red ScotchBrite soaked in acetone. The acetone does seem to slightly soften the primer for a better adhesion. This worked for him and many of the other early South Bay RVs - those completed in the early 90's - and with good results.

The fact Akzo makes it solely to a Boeing specification is the reason they don't give any details about topcoating, since I'm sure Boeing leaves it as sprayed.

Gil in Tucson - but lived in Los Angeles for 22 years before....

PS Steve Barnard's RV-6A was the one CAFE tested...
 
Thanks for the suggestions

Thanks for the responses.

I have the datasheet & MSDS and understand the AKZO's usage. I'm interested in technique/tips for what others have done (i.e. Did you prime these exposed spars/ribs with it? Did you use a different product on just these portions? Or -- my current thinking -- did you leave just the portions that will get paint in the future exposed for now?)

It sounds like going ahead and priming them now could be dealt with later, but as Dan mentioned, I don't like the idea of having to use solvents/chemicals to remove it for fear of the stuff sitting in between mating surfaces eating away at the primer I want to keep. I guess just putting some elbow grease into roughing it up might be an alternative too since the quality of the paint in this area probably isn't that big of a concern. But I think the easiest might be to just leave these areas bare for now. I'm considering this a viable alternative since these parts will be stored in our house until final assembly begins. Now that I think about it, alodining these parts and not using primer on these surfaces is probably the way to go.

Thanks again.
 
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