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Bead Blasting/ Etch Primer

I’m familiar with the large number of products to prep aluminum previous to painting and I’m not excited about using any of them. I’m working on an RV14 and not planning to prime or paint everything but where parts are joined together (aileron brackets, flap brackets, rib to spar, etc) I’m thinking about lightly bead blasting those areas and priming them with SEM etch primer. The surface left from the bead blasting supposedly relieves stress in the metal and takes small scratches away. As far as adhesion is concerned a bead blasted surface certainly has more “tooth” to it than most other treatments. Anyone tried it?
 
Probably best NOT to bead blast the surfaces. Successful priming is achieved without that, with no damage to the alclad surface or the fairness of the part.

All you need is maroon Scotchbrite to abrade the surface and some suitable solvent to clean it. I've used lacquer thinner, denatured alcohol and isopropyl alcohol successfully for that, along with SEM, a couple of rattlecan zinc chromate or phosphate primers and Stewart EkoPoxy. Of those, the SEM and the EkoPoxy are the best.

The thread on Primers covers a multitude of opinions and comments and is worth reading.

Dave
 
I’m familiar with the large number of products to prep aluminum previous to painting and I’m not excited about using any of them. I’m working on an RV14 and not planning to prime or paint everything but where parts are joined together (aileron brackets, flap brackets, rib to spar, etc) I’m thinking about lightly bead blasting those areas and priming them with SEM etch primer. The surface left from the bead blasting supposedly relieves stress in the metal and takes small scratches away. As far as adhesion is concerned a bead blasted surface certainly has more “tooth” to it than most other treatments. Anyone tried it?

No stress in hardened / tempered aluminum or un-hardened 6061-O for that matter; Not dealing with cast iron or welded steel here. I would NOT use bead blasting. Simple maroon pad (320-400 grit). If you want more tooth, use 220 grit sandpaper. Two coats of most epoxy primer will fully cover those scratches. No need for self etch primer if you are mechanically etching the metal (i.e. sanding or scuffing). Most painters don't like the acid left behind with self-etch; Problematic for adhesion of the next coat.
 
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It is more important the interior surfaces are covered with some sort of primer or paint, doesnt matter if its etching although etching would be better. If you saw all of the corroded interior surfaces I find on airplanes I work on, some even relatively new, even experimentals...you would prime everything. You dont need to be near the oceans. In fact the large temperature swings as one encounters in the midwest will cause corrosion. I have literally seen wings dripping wet on the inside after a prolonged cold and sudden humid warmup.
 
Bead blasting sheet aluminum tends to make it warp, and it removes the pure aluminum layer on alclad. Don't do it.
 
It is more important the interior surfaces are covered with some sort of primer or paint, doesnt matter if its etching although etching would be better. If you saw all of the corroded interior surfaces I find on airplanes I work on, some even relatively new, even experimentals...you would prime everything. You dont need to be near the oceans. In fact the large temperature swings as one encounters in the midwest will cause corrosion. I have literally seen wings dripping wet on the inside after a prolonged cold and sudden humid warmup.

Interesting. My 1957 C-172 lived a hard life between being tied down outside and being hangared in northern Wisconsin, Illinois, and SE Indiana. It was not primed and showed little to no corrosion over the 20 years I owned it…
 
Interesting. My 1957 C-172 lived a hard life between being tied down outside and being hangared in northern Wisconsin, Illinois, and SE Indiana. It was not primed and showed little to no corrosion over the 20 years I owned it…

What you are describing is impossible. I have a 150 that's spent most of its life in hangars in Indiana and there is a fair amount of corrosion in the wings.
 
Depending on sun angle, drainage slopes and insulation or lack, ventilation or lack, the same two planes in two separate hangars can have totally different exposures. I've seen nice air, high and dry in one and around the corner facing opposite another hangar is almost raining inside.
 
Really

What you are describing is impossible. I have a 150 that's spent most of its life in hangars in Indiana and there is a fair amount of corrosion in the wings.

We will have to agree to disagree. Pretty sure I know the airplane after owning it for 20 years…
 
I have to agree with Bob. I've seen a lot of older Cessnas with little to no corrosion.

I worked with "Corrosion Control" extensively on our C-124s in the Air Force, so I do know what corrosion looks like.
 
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Probably best NOT to bead blast the surfaces. Successful priming is achieved without that, with no damage to the alclad surface or the fairness of the part.

All you need is maroon Scotchbrite to abrade the surface and some suitable solvent to clean it. I've used lacquer thinner, denatured alcohol and isopropyl alcohol successfully for that, along with SEM, a couple of rattlecan zinc chromate or phosphate primers and Stewart EkoPoxy. Of those, the SEM and the EkoPoxy are the best.

The thread on Primers covers a multitude of opinions and comments and is worth reading.

Dave

+1. Bead blasting can also remove metal you would rather not remove. Trouble is, you won't be able to tell.....until......something breaks. In addition to heat warping, the heat can change the characteristics of the metal. Also, not good.
Maroon the parts, clean and prime away.

It's what I did and I have no regrets. The time, and cost is negligible compared to the near guarantee of no corrosion for difficult to see, mated parts. You will probably never sell your project, but if a prospective buyer is living in Biloxi, primer will be a selling point.

Just my $0.02.
 
I have to agree with Bob. I've seen a lot of older Cessnas with little to no corrosion.

I have too and more often than not they have varying degrees of corrosion. That said my Comanche has nearly zero corrosion and there is virtually no possibility of it internally as it was zinc chromated despite it having a rodent infestation at one point in its life. Rodent droppings release ammonia gas which creates a corrosive atmosphere.

Point is its better to have corrosion protection internally than not.
 
Certainly

I have too and more often than not they have varying degrees of corrosion. That said my Comanche has nearly zero corrosion and there is virtually no possibility of it internally as it was zinc chromated despite it having a rodent infestation at one point in its life. Rodent droppings release ammonia gas which creates a corrosive atmosphere.

Point is its better to have corrosion protection internally than not.

It's certainly not going to hurt anything but it does take a bunch of time and adds weight.

It really comes down to, "Do you want an airplane that will last for 100 years or 150 years?"
 
The surface left from the bead blasting supposedly relieves stress in the metal...

I actually did graduate research on this!

Bead blasting aluminum would likely have a similar effect to "Shot Peening" titanium. The effect is to actually CREATE residual stresses in the surface.

You can think of it as essentially compressing or burnishing the surface. Main difference is that the net shape and volume remains the same.

The positive result is that, ideally little to no material should be removed, and the resulting surface _should_ be more resistant to crack formation.
 
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