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First Alodine Experience Bad

rwagner24

Active Member
Hey guys,
I am building a RV8 quickbuild that sat in a hangar in Pa for about 8 years. The surfaces of the wings and fuse have light white corrosion. I just finished the tail so It will still be awhile before I get to the priming stage of the wings. I wanted to do somthing to clean them up and protect them in the mean time. I have had many suggestions from polish, alodine, prime and just wash with dawn and build on. I talked with a corrosion guy at osh this year that said to alodine them so this weekend I tried and the came out bad. Here is what I did and the pics show what I got.
1 Washed well with a warm water/dawn solution towl dried.
2 Washed with Aluma Prep mixed 1:3 with water let on 3 mins rinsed
3 Found some spots that didnt come off and ended up scotchbriting the whole wing. ReAluma Preped and rinsed. Made sure water didnt bead up.
4 Let dry completely overnight in garage.
5 Wiped down with full streangth Alodine let sit 3 mins rinse.

The thing looks like some tie die shirt from the 60's I Re did the aluma prep wash and alodine and it looks pretty much the same. I'm thinking let it alone till primer. I have the other wing and fuse to do though. Any suggestions?

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They look pretty normal to me... that's about what you would expect. Cosmetically they ain't pretty until you get the first coat of primer on them. I would do the same to your remaining parts: wash with Dawn, aluma prep (muriatic acid), alodine. If you want a little more consistent look, leave the alodine on a little longer. You can experiment with some scrap, but the older the alodine is, the longer you want to leave it on. It loses its strength over time or if you use the same batch more than once.

You could also give everything a light coat of primer for more protection.
 
no worries

The blotchyness is partly from spots you scotchbrighted more aggressively, and partly from places where the alodine went on fresher or stayed longer. Try leaving it on longer to build a thicker passivation layer, and perhaps a bit more consistent look.

But really, no one cares what it looks like at this stage, just good protection
 
I found that the parts that were too large to soak, like the skins came out blotchy. It was just caused by the inconsistant layer of alodine that you could keep on the surface at any given time, no worries.:)
 
I like to include a more aggressive solvent in the cleaning steps. I like 100% isopropyl alcohol I get at Frys (an electronic chain store), but MEK or acetone should work too. And rinse with distilled water, and/or at blow dry with shop air, just before the alodine.
 
Ok thanks guys just thought it would have a more even coat. I guess there is more protection there than there was before. I will try wiping with mek or alcohol on the next wing. Not gonna worry about it anymore it will be primed with epoxy later and never seen again.
 
Also be careful handling the freshly alodined parts as the new coating is VERY soft and takes about 24 hours to harden. My tail skins came out blotchy but all the other parts that could be soaked came out nice. Remember to keep the surface wet the entire time and do not allow alodine to dry on the surface. Rinse gently and then allow to air dry.
 
The etch instructions lie to you.

Do NOT let the rinse water from washing off the etch acid dry before applying the Alodine. With old, corroded aluminum, letting the rinse water dry simply allows the corrosion to reform. Alodine will ONLY take on CLEAN aluminum. This is one process that absolutely requires cleanliness. Apply the Alodine while the rinse water from the etch acid is still damp.
Charlie
 
Details

As others have said, the alodine is completely normal. That said, I too am a bit turned off by the splotchy look. It is strictly a temporary cosmetic thing that doesn't mean much in the overall scheme of things. That said, to separate myself from the pack in the production environment where 99 guys out of a 100 were perfectly happy to "settle," here's what I did to achieve a more uniform looking coating. I would first lightly moisten with water (strictly speaking it should be deionized water but who cares ) a piece of cheesecloth then soak the cheesecloth in alodine. Next, I would uniformly wipe the subject surface down with that alodine soaked cheesecloth and let it set briefly before rewiping the surface with pure water. That technique went a long way towards achieving a more uniform golden color. I used often used that same technique when building my RV's with similar pleasing results.
 
The one thing that might be poor on your wing is what looks like a hand print on the top of the first picture.

Perhaps it had "greasy hands" on it in between steps?...:)
 
Ok then maybe not rinse with a pressure washer then either

Seriously? Lol
If you did, then you should consider re-etching and re-alodining because you just blew away most of the coating. I'm going to try a cheesecloth or natural sponge next time I alodine skins, seems like a pretty easy way to keep the surface wet as you're working.
 
Spray it on

A trick I have used on other projects for parts that were too big to dip in my alodine bath was to use spray bottles to apply alumiprep and alodine. Obviously wear a respirator since you are putting the chemical airborne and wear chemical resistant gloves. I recommend goggles too.

Get two spray bottles. Fill one with the alumiprep solution, the other with alodine. For big stuff like this I would soap and water wash the piece well, rinse and blow dry with shop air. Wipe down with MEK or acetone or lacquer thinner, anything to remove remaining oils. Using the spray bottle filled with alumiprep solution, spray the entire surface with alumiprep and start scotchbrite-ing. Just keep the whole area wet with alumiprep using the spray bottle and scotchbrite it for the full three minutes. Rinse it well with a hose. Before it has a chance to dry, spray on the alodine. Use the spray bottle like a paint gun to apply an even coat. It won't be perfect like you had dipped it but it will be much more even coverage than wiping.
 
A trick I have used on other projects for parts that were too big to dip in my alodine bath was to use spray bottles to apply alumiprep and alodine. Obviously wear a respirator since you are putting the chemical airborne and wear chemical resistant gloves. I recommend goggles too.

.....

Make sure you buy the cheap plastic spray bottles at the dime store with plastic internal parts. The better ones with metal inside parts don't last to well with acid etch...:rolleyes:
 
Do NOT let the rinse water from washing off the etch acid dry before applying the Alodine. With old, corroded aluminum, letting the rinse water dry simply allows the corrosion to reform. Alodine will ONLY take on CLEAN aluminum. This is one process that absolutely requires cleanliness. Apply the Alodine while the rinse water from the etch acid is still damp.
Charlie

That isnt entirely accurate. Aaluminum oxidizes the instant it is exposed to oxygen. It is this oxide layer that the alodine chemically converts. If you were able to clean and prep your skin in an ox free environment then the alodine wouldnt work at all.
 
Make sure you buy the cheap plastic spray bottles at the dime store with plastic internal parts. The better ones with metal inside parts don't last to well with acid etch...:rolleyes:

Yes, I should have mentioned that no matter what type of bottle you use, they don't last. Always have a spare set on hand because as soon as you begin the process on an evening when the stores are all closed and won't be open the next day...the sprayers will both fail. Murphy restores and builds airplanes too.
 
I go through a lot of spray bottles. Alodine will tend to clog the nozzle after a few weeks of sitting around. Cleaner and etch will last much longer. The best bottles I've found lately are from Home Depot. The cheap clear ones with the yellow and blue top.

I would like to see a little more gold color in the OP's alodine job. The unevenness doesn't bother me to much. You might try and do the etch step two times then let your alodine sit just a little longer before you rinse. If you still don't have the color you want, apply the alodine again. Hope this helps.
 
Dry Alodine

I see everywhere that one should not let alodine dry. Why is that? I recently did a VS skin and some alodine leaked throught a dimple through to the other side and dried. What are the implications? How do I clean it of?? Sand it? If so, I assume that the dust residue is carcinogenic. Any advice appreciated.
 
I see everywhere that one should not let alodine dry. Why is that?

No issue with letting the Alodine (chromic acid) dry. Rinse eventually or wipe (lightly) off any powdery residue with a damp cloth.

It is the phosphoric acid etch (Alumiprep) that you do not want to dry on the skins/joints.
 
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