Bead Blasting/ Etch Primer

[Wayne Stambaugh]

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?

[David Paule]

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

[lr172]

Originally Posted by Wayne Stambaugh

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.

[rocketbob]

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.

[DanH]

Bead blasting sheet aluminum tends to make it warp, and it removes the pure aluminum layer on alclad. Don't do it.

[rocketman1988]

Originally Posted by rocketbob

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…

[rocketbob]

Originally Posted by rocketman1988

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.

[Wayne Stambaugh]

I should have known how this was going to end up. Primer wars, however thanks for everyones input.

[moosepileit]

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.

[rocketman1988]

Originally Posted by rocketbob

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…