Conversion Coating?

Hi all,

I am thniking about having a go at painting my RV 8 at home. I am trying to sort out the preparation of the aluminum issue. The EAA paint your plane manual calls for alodining the aluminum surfaces. The best way to do that is clean with alumiprep (phosphoric acid) with a light scrubbing with scotchbrite, rinse and then spray with alodine. Let it set for a little while and rinse off. Then prime and top coat.

The problem is, the alonide is a serious environmental hazard and I don't think I can reasonably use it at home. For most of my interior structures (ribs, bulkheads) and used a conversion coating by Sanchem. Very similar process except that it uses very benign chemicals. By the look of it, I think it is a permanganate solution. At any rate, priming over it with AZKO Nobel worked really well.

Moving on the my fuselage exterior, the folks at Steward systems basically say to etch the aluminium with their prep (another phosphoric acid solution) and then prime and top coat. No conversion coating necessary.

Loehle products describe using alodine http://www.loehle.com/loehle_aero_coatings_on_rv_aircr.htm

I could go with the Sanchem approach. The principal question is, do I need to do a conversion coating on the aluminum. I really value the opinions on this site. What do you guys think? Any painting professionals out there way to weigh in?

Regards,

Michael Wynn
RV 8 Finishing
San Ramon, CA

Sol-gel

I have been looking at this to use for paint prep.

http://www.actechaero.com/tech-data-sheets/131-AC-03-10HC.pdf

It is a non-hazerdous conversion coating of metals that promots adhesion by bonding a sol-gel surface onto the metal that leaves bond sites open for primers and paints.

I have not tried it, but know someone who has and say it works. The AC Tech website offers suppliers for the product.

I believe PPG also has a version of this licensed from the same developer, but I don't have the product number.

Soap & water and a gray scotch-brite pad, worked well for my RV exterior. I let it dry over night, and used a paint cleaner or Coleman lantern fluid to clean the dust, and then a tac rag before priming & painting in the morning. Sherwin Williams "Genesis" paint. Paint has been on for over two years, and still has a new look, as well as adhesion. No other special chemicals were used.

L.Adamson --- RV6A

I'm in the process of painting my RV-6 and did use alumaprep and alodine, however, I started out to use Sherwin-Williams wash-primer and then my hot rod paint buddy asked why I was using a wash primer and alodine. I answer I gave him was that a number of years ago Van's used wash primer on their quick build kits when they were built elsewhere and I figured if they used it it must be good. He told me you should use one or the other process, so I did use the alodine and will prime and base coat tomorrow. By the way the Sherwin-Williams part number is P60-G-2, part A and R7-K-44, part B. Good luck!!

Scuff, clean, and epoxy

I've painted two RV's now and have talked too countless other builders about this. The traditional method of etch, alodine, prime does work, but it is NOT necessary. Modern automotive (such as PPG DP) epoxy primers are designed for adhesion on scuffed aluminum.

I've been very happy with the follwing. Use soapy water and scuff with a gray (or red) scotchbrite pad to a totally sating finish. Then clean and DRY thoughly with compressed air. I use rubbing alchohol and lots of paper towels to produce a totally clean surface. Then shoot the epoxy and whatever topcoats that you want.

Another friend of mine did this exact thing on his '6 about 12 years ago. Still looks great with no adhesion issues.

I used Pre-Kote on smaller parts

Alodining at home is ugly. I did much of it myself when I started my -4, but was never comfortable with the environmental issues. After completing the tail section, I started to use local platers to alodine parts. Every few months, I would bring as large a batch of parts as I could collect to a local plater and pay a lot charge to have everything alodined. It generally cost $75-$150 per lot and took less than a week.

After the plane was completed, I used Pre-Kote when I built a new rudder. From everything I read, it is supposed to provide adhesion as good as alodine, but is easier/cheaper/faster to apply. It appears to have worked, though when I had the rudder topcoated, the aircraft paint shop I used said that they had poor results with Pre-Kote and still relied on alodine.

Guys, keep it simple.

If there is a lot of dirt on the surfaces, get it outside and give it a good wash with a very simple soap and water - try baby bath - no salt, no wax.

Then, when dry, or if you don't need to wash - scuff the whole surface with red Scotchbrite - please get the real stuff, not a cheapo brand. 3M products just do it correctly.

Then, go over the whole aeroplane with Alumiprep from Spruce - a mild acid brightener - you really see the surface clean up.

Swill off with water, let dry in the sun, then spray on 2 part etch prime, build prime and sand, shoot colour, stand back, admire !

This is a post for all of you who have posted here and anyone else who has expertice in priming and painting an airplane. I am building the 4, and I am absolutly ignorant of knowledge in the area of priming and painting! I am in the process of convertiing my shop for the build, so I have a little time to decide. My first question is what do I need to decide before I begin? Is it better or required to prime parts before assembly? I have read on the forum that some builders even debat whether to prime at all? I am still considering whether to paint or polish the exterior, what if any part will this decission play in how the inside of the aircraft is primed and or painted? How much weight does the average prime and paint add? If it helps to know, I am fussy and want to build a nice airplane. Because of my ignorance, please be as complete with your answers as you have time for. THANKS!!!