Alodine Techniques anyone?

(first of all I don't want to make this a alodine vs [insert corrosion prevention technique here] thread...

I've never worked with alumaprep, nor 'alodine' before...

Got some time yesterday to work on the plane... needed to prep for priming. So I mixed up some alumaprep, put it in a bucket and scrubbed everything...

Poured the old alumaprep in a gallon jug rinsed the bucket good and went to alodining... well the small parts turned out great, the long ones, not so much... if I couldn't lay them flat and imerse them it was splochy at best (think stiffners, to spars)...

So I got some 4" PVC and made long 4', 6' and 11' tanks by capping them then sawing off the top just above half way... Think I'll try them on the spars/stiffners today...

Anybody got a good technique they could share? Can I re imerse the long pieces with success?

It seems like you got the right approach. I have a variety of containers that I use depending on the parts I'm treating. I use the long shipping crate from the tail kit lined with plastic. I drilled a hole in the end of the container. When I'm done, I poke a hole in the plastic and drain back into my gallon jugs for storage.

The large skins are awkward at best. I just use a foam brush and paint the alodine on. It doesn't work as well as immersion, but it's better than nothing.

I made a temporary immersion tank for the big pieces, including my fuel tank skins, but tacking some 2x4's on my workbench and lining it with plastic, then dipping the parts in the alodine in that tank. The alumiprep is much less picky - stand your long parts vertically in a bucket or cooler and brush them down, then rinse off and dip them in the tank of alodine.

There are as many ways of doing this as people building, but this worked for me.

If you don't mind me asking, how hard is it to work with these products? Can you just hang the pieces on a rack in the driveway and rinse them down with a hose? Do you need any kind of respirator to work with these things? They seem like they must be sme type of chemical. Thanks!!

The alumiprep is mostly phosphoric acid for etching the aluminum, it's relatively benign. It will do a number on your concrete if you leave it set there, though.

The alodine solution is chromic acid, and is more importantly hexavalent chromium, which you don't really want to expose yourself to more than necessary, as it's pretty hard on your liver and is a known carcinogen. For the same reason, you don't want to dump it in the alley when you're done with it. Respirators are not needed, just use rubber or latex gloves and I wear safety glasses for splashes. It's not gonna kill you quick if you get some on your skin - just rinse it off and go on - the idea is to limit long-term exposure and remember that it's about as safe as smoking unfiltered cigarettes - less is always better.

Thanks! I tried looking for the prep discussions but can't seem to find any meaty ones.

I find that...

airguy said:

...... The alumiprep is much less picky - stand your long parts vertically in a bucket or cooler and brush them down, then rinse off and dip them in the tank of alodine.

There are as many ways of doing this as people building, but this worked for me.

Click to expand...

The Alumiprep can be applied with a spray bottle (plastic internals only) and then the work gently rubbed with red scotchbrite.

This ensures the etch getting everywhere, and gives an extra "tooth" for the future paint.

Even if you dip, using red scotchbrite is still a good idea...

The acid level of the diluted Alumiprep is way below that of hardware store pool acid... rubber gloves and safety goggles work fine.

I haven't used the spray bottle idea, I'll have to give that a try. I usually just dip my scotchbrite pad in it and scrub the surface of the part I'm etching. The alumiprep is relatively mild as far as acids go with respect to your skin - if you get some on you and leave it there long enough, it will start to burn and itch and make you want to get it off you - but that's about it.

....Anybody got a good technique they could share?....

Click to expand...

Years ago, I was part of a small crew working on an F/A-18 Hornet wing flap modification program. Each member of our crew was assigned one well used wing flap and each of us reworked that one flap until it was completed, thoroughly inspected by both the company and the customer rep who ultimately approved the flap for release back into the fleet. The often complicated processes involved to modify and refurbish each flap could easily take several weeks. By far, the hardest part of the job was grunt work....spending 8 hours a day and up to a week and uncounted dozens of drill bits just to drill out the hundreds of jo-bolts and cherry rivets from the flap?s composite skin. Every hole you screwed up in the drill out process was documented and brought up oversize. Nothing got past QA! As part of the retrofit program, a rectangular section of aluminum had to be alodined prior to fitting the new piece to the leading edge of the flap. We had no alodine bath to dunk the part into.

Using traditional disposable chip brushes, all of the aluminum pieces my co-workers alodined came out splotchy. From a quality standpoint, the splotchy looking alodine was acceptable even if cosmetically ugly. It really didn?t matter much because everything was going to be painted over anyway. Still, my work consistently appeared to have an even golden hue over the entire surface of the aluminum part. It was a pride thing. One day I was asked by supervision how it was I could make the alodine finish look so consistently even hued while the other worker's flap piece always came out splotchy. My secret? First, using MEK or equivalent, I made sure the part was thoroughly clean and dry all over. Second, I very lightly moistened a piece of cheesecloth using the required deionized water. Psst: Common drinking fountain water seemed to work just as well. I then liberally brushed the alodine onto the surface like everybody else but would immediately follow up by gently wiping the aluminum with the lightly water moistened cheesecloth in an attempt to work the alodine into the surface of the aluminum as evenly as possible. After a few minutes, I then neutralized, rinsed/wiped the alodine off using a fresh new piece of clean cheesecloth liberally wetted down but not dripping with clean deionized water. The result was a consistent and even golden hue over every square inch of the part. When my ?secret? got out, the procedure became SOP.

This is what I was hoping

Lots of good posts here fellas.

Thank you for the suggestions and info. (and not making this a typical corrosion control bashing/misinformation/you don't need to do that thread).

I spoke with a local guy who's finishing out his fusesalage on a 7... he recommended I switch from the grey to the red scotch bright and scrub each piece longer... I think I really didnt take off the alclad in a few spots and that contributed to the splotching... also the imersion seemed to help some of the pieces too...

next time I'll scrub better and start with an emersion tank...

primed the pieces today and riveted my first few parts together... it was nice finally squeezing some rivits!

once the alodine dries even for a second its done all the soaking in the world makes no difference. it must stay wet for a darker color and even coat. you can remove it with hot water. the hot water will first remove the color if you want it to be clear, but must still be flushed with hot water to remove the alodine. then you can reapply it. it must stay wet for an even uniform coat.


here is a pdf on the use of alodine. spruce doesnt seem to have much in the way of instructions for alodine. http://www.pegasusautoracing.com/productdetails.asp?RecID=5590

Instructions for brush-on...

...from Iridite here....

http://galladechem.com/specs/macdermid/78660.pdf

...but Rick's method seems better...

Iridite supplies grey ScotchBrite pads.... but the kit may not assume that a primer is being used as a next step and wants to make a more decorative finish.

I still prefer the red pads....