nohoflyer

nohoflyer

Well Known Member
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I just flew with an ex A+P from a legacy airline. We were talking paint. He asserted that you have to prime the surface before painting or else the paint won’t stick. What I’ve read on here goes against that…I think.

Thoughts?
 
Aluminum is not conducive to paint adhesion…so one of the most proven processes is to etch the surface of the material with a product such as Alumaprep, then coat it with Alodine 1200. This is an acid etch, followed by a chromate organic conversion coat. You end up with a lightly gold hued aluminum airframe, which can then be primed. The etch and alodine opens the pores of the aluminum, if you will….andcreates a toothier or more porous bond surface.

Most paint systems have their own recommended primer to go with their color coats and following the manufacturers advice , usually gets you a decent bond on a paint job.

The idea is: the paint stick to the primer, the primer sticks to the organic conversion coat….the conversion coat sticks to the aluminum.

I’d stick to that concept if you want a nice paint job.
 
Not true, but some epoxy primers do have stronger adhesion to metal by design and therefore helpfull when working with Alum. The paint can grab better to the primer than the tougher surfaces. Paint is porous and will allow corossion on base metal over time. Primers primary role is to prevent that, as well as being a stronger base (different properties). Several other reasons/benefits also.
 
lr172 said:
Not true, but some epoxy primers do have stronger adhesion to metal by design and therefore helpfull when working with Alum. The paint can grab better to the primer than the tougher surfaces. Paint is porous and will allow corossion on base metal over time. Primers primary role is to prevent that, as well as being a stronger base (different properties). Several other reasons/benefits also.
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What Larry ^ said.
Think of it this way...
Have you ever painted a rusty steel part just to cover it? Rust, iron oxide, finds a way. Paint chips off.
Aluminum Oxide is the same. Sort of. It's a hydrophobic layer. Water doesn't stick. Paint doesn't like it either. That's why we scuff and scrub to get a hydrophillic surface. Some call it a water break free surface. Water forms a layer instead of beading. Much friendlier to paint. Next is usually Alodine or Epoxy primer as soon as possible. Aluminum oxide starts forming immediately. I've discussed the process with some serious paint guys. They actually go further. They add a wash primer like P60G2 before the epoxy primer.

All that said, it really comes down to where the plane lives and how long the builder wants it to live. Alodine adds protection with zero weight. A very thin layer of wash primer like P60G2 is almost weightless. Epoxy heavier. Epoxy and paint, heavier still.
 
Bandera said:
Primer sticks to bare metal better than paint does. Paint is really good at sticking to primer.
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And paint is better at protecting the primer and metal from corrosion than the primer is. My 1993 Super Cub was primed and then clear coated on top of that. The Super Koropon primer failed on the space shuttle until they discovered this.

Read the manufacturer's instructions, sometimes there is a 'window' for applying the topcoat.

D
 
nohoflyer said:
I just flew with an ex A+P from a legacy airline. We were talking paint. He asserted that you have to prime the surface before painting or else the paint won’t stick. What I’ve read on here goes against that…I think.

Thoughts?
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Anything that has paint on it needs primed but what the "primar wars" are is whether or not to prime the bare aluminum parts that don't get painted for corrosion protection.
 
Not all primers adhere to bare metal better…but those self etching primers definitely do.

It really is best to decide on the system you want to use and ask what the manufacturers or a certified paint facility recommends and follow their instructions.

I’m not aware of any of the major paint suppliers for aircraft advocating against etch, alodine, prime and topcoats.
 
Aerodon said:
And paint is better at protecting the primer and metal from corrosion than the primer is. My 1993 Super Cub was primed and then clear coated on top of that. The Super Koropon primer failed on the space shuttle until they discovered this.

Read the manufacturer's instructions, sometimes there is a 'window' for applying the topcoat.

D
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There is a window for doing wet on wet. Usually 24 hours or less. I prefer to let the primer cure then sand it. You get a better, smoother finish that way. IMHO.
 
My plane was built in 2014. Builder used some kind of prep wash (not acid etch or alodine). It cleaned the surface well but it’s too slick, the surface wasn’t abraded before paint.
Painted with Imron and now that it’s aging it’s popping off in places.
 
We need @HFS to weigh in on this thread. He painted his [my] Rocket II over 24 years ago and the paint looks better than most brand new out of the booth paint jobs. Seriously. Not even any flaking around the skin dimples for countersunk screws that come on and off an average of at least a couple of times per year. Truly impressive.

My answer is to do whatever David did!
 
Way back, almost 30 years ago Vans recommended to paint without primer, to save weight. (about 25 lbs)
So on my RV8 I painted the parts without primer as I built them, and assembled the plane and added vinyl stripes.
I flew the airplane for 18 years, kept it in a hangar, but I did many overnights on ramps in all kind of weather and hostile climates. The paint never lost a single chip of paint, except for a very few tiny ones on the leading edge of horizontal stab, from gravel and dirt runways. Tiny chips easily fixed with a paint pen, like when somebody smashes their car door into yours.
I'm going to do it again on my current build, pocket the $40K, and let someone else get the trophy.
 
Chukill said:
Way back, almost 30 years ago Vans recommended to paint without primer, to save weight. (about 25 lbs)
So on my RV8 I painted the parts without primer as I built them, and assembled the plane and added vinyl stripes.
I flew the airplane for 18 years, kept it in a hangar, but I did many overnights on ramps in all kind of weather and hostile climates. The paint never lost a single chip of paint, except for a very few tiny ones on the leading edge of horizontal stab, from gravel and dirt runways. Tiny chips easily fixed with a paint pen, like when somebody smashes their car door into yours.
I'm going to do it again on my current build, pocket the $40K, and let someone else get the trophy.
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THAT is why I recommend testing for yourself. It's Experimental. The FAA defines it as Education. Experimental & learn. 20lbs and $40K is a heck of an education. Almost a year at a major university. Thanks for posting.
 
30-years ago when I was getting ready for paint, I learned one thing. FOLLOW the paint manufacturer recommendations.

3-decades ago, MOST paint manufacturer that had products that I was considering, all recommended primer 24 to 72-hours before top coat. Most recommended sanding the primer before the top coat IF the primer had not been applied within the recommended time frame.

Find out what the paint manufacturer you are using recommends and follow all of their steps.
 
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