Metal prep?

Do I really need to "prep" the metal before using a wash primer? At the place I got the primer, they have never heard of such a thing, they only and allways scuff the metal with scotch brite.

I can get some DuPont 5717S metal conditioner, but according to the tech sheet, aluminum is not mentioned...

That's for steel....

SvingenB said:

Do I really need to "prep" the metal before using a wash primer? At the place I got the primer, they have never heard of such a thing, they only and allways scuff the metal with scotch brite.

I can get some DuPont 5717S metal conditioner, but according to the tech sheet, aluminum is not mentioned...

Click to expand...

Wrong stuff... that is part of the combination for steel.

You need the Dupont 225S and Dupont 226S combination for aluminum acid etch and alodine.

If you only need the acid etch, the 225S is the stuff to use...

http://www.performancecoatings.dupont.com/dpc/en/us/html/prodinfo/chromasystem/H-19290_225S.pdf

gil A

Thanks, that saved me alot of money. The car paint shop that could get the 5717S, could anly get a pack of 6 (6 x 1 L), and I had to purchase all of them because they never use it themselves, and never sell any. Getting way too much of the right stuff is bad enough, but getting too much of the wrong stuff is totally crazy.

But do I really need it. Wouldn't scotch brite and water + MEK (or similar) do exactly the same thing when using a wash primer as the primer? Has anyone successfully used a wash primer with no dedicated cleaner?

I chose Sherwin Automotive E2G 973 Vinyl Etch Wash Primer (Zinc Chromate).

It does not require sanding or roughing up of the aluminum substrate, just cleaning (I used MEK). This is according to the Sherwin recommendations.

This saves tons of work. After this product cures, it does not flake or peel off the bare aluminum. You can scuff the Alclad, but it's not necessary.

You do not need to etch, and you cannot alodine before use. For your favourite Wash Primer, check the instructions.

Vern

E2G 973

Vern,
Interesting that you bring up that primer. Did you topcoat anything primed with it? I'm supposed to meet with the local SW rep this week concerning that primer. I'm working on the fuse and am about to prime and paint the interior and want to use this. I know Mel has used it and I think it has to be topcoated with something prior to painting. Anything you can tell me will be appreciated.

vlittle said:

For your favourite Wash Primer, check the instructions.

Vern

Click to expand...

Thanks. The instruction say "cleaning/sanded paper P600-800 wet or -320 dry" and that it must be free of oil and silicone - that's it. The guy at the truck body shop where I got the primer said I should use scotch brite (red/maroon?) and clean with "Lynol" (similar to MEK I guess). But that is not the problem. The problem is that I contacted the factory in France to be sure that this primer could be used on alclad and not only on thick aluminum plates for trucks. The guy at the factory said of course, Air France and Eurocopter use this stuff, but I should use this "Derinoxalu" washing thing. This mystic Derinoxalu is not even listed at the factory web site, and the paint shops here in Norway cannot find any reference to it.

So whatever reason (language problems, communication or whatever), I simply cannot get hold of the stuff.

Living far away from the (or any at all) centers of aircraft building sure has it's own sets of problems regarding materials. So right now I am more in the mood of treating my RV like a truck, that is scotch brite and Lynol.

btw do these scotch brite pads have any P rating like normal sand paper ?

I don't know the answer to your problem, but just want to point out that Alodine contains chromates which are carcinogenic and have disposal restrictions. You can ignore the letter of the law & run it down the drain, but in most municipalities in the USA you will be in violation. It is probably not wise if you have a well and no sewer system. Whether you ever get caught running it into your municipal sewer system is another question.

The environmentally friendly alternative is Prekote which you can buy at Aircraft Spruce. Purchase price is higher than Alodine but is supposed to actually be cheaper. Here's what Aircraft Spruce says in their catalog: "...By eliminating the need for chromated conversion coatings (such as alodine), acid etches, solvent washes and other toxic processes, PreKote® can reduce paint preparation time and costs by up to 40%..." The US Air Force uses it along with Boeing and some major airlines. Prekote is biodegradable.

Interior parts do not need Alodine or Precoat. Just use Scotch Brite, degrease (I use acetone) and prime. At Oshkosh, all the paint shops I talked with said exterior surfaces need Alodine or some similar treatment.

Richard Scott
RV-9A Fuselage