Alodine and Alumiprep

Hello all,

I'm practising with alumiprep and alodine as that's what I intend to do on my RV14A rather than Priming.

Not sure if I'm doing it correctly though. The following link is to my Vans Tool Box kit and images of how it turned out with Alodine.

http://www.rv-14a.net/blog/another-practice-project

Would be great to hear some hints or tips as to whether I'm doing it correctly or if I need to do.

Thanks in advance.

Clean off the red mill stamping with MEK, or some other solvent. Alodine finish will be damaged during assembly. If you feel you must go down this path, use it as a base for primer, not as a final finish.
Just my opinion.
DaveH
BTW, I'd get rid of that claw hammer asap. It's a wood butchers tool. Has no place in a metal workshop

Hi Ian,

Through some experimentation of my own, it appears to be a cleanliness issue.

I dip my parts, so let's start with that. I clean the parts with mineral spirits to get sticky stuff, and then wipe with a wet towel of alcohol. Denatured or rubbing (ethyl or isopropyl) all over. On small parts without label adhesive, acetone works too. I just don't like the smell. Dip in prep solution for 2-3 minutes, rinse in distilled water (sometimes just spray down small parts with hand sprayer), then dip in alodine for 2 1/2 minutes - or longer if weak to match colors. Rinse in new water, blow dry with shop air and hang for 24 hrs. That cured my mottling. Try these on your own for a starter.

Any other cleaning process you want to ask about - I probably tried it. Many worked but this seemed to must efficient and I stopped experimenting. Plastic buckets, 3" PVC tubes (vertical), and large plastic storage containers have been used.

Last thing - I had some corroded 2024 .063 and it looked pretty bad. It needed some scotchbrite to level the surface, then the other steps left a nice finish.

"The process"

So,
Not to start a "pre-primer" war, and following the process used by virtually all the major aircraft manufacture and repair process, (my day job), I will put into laymans terms the basics.
The aluminum as delivered is either "Alclad" ( most all sheet stock), or "bare", (most all extrusions). During the finish process of painting, the aluminum needs a good cleaning, either mechanical (Scothbrite,ect.) or chemical (Alumiprep,ect.). After cleaning, the Alodine is applied as controlled acid etch which seals and promotes adhesion for the yet to be applied primer/paint. Some people choose to eliminate priming, and directly apply the paint topcoat, which I personally don't recommend. Its hard to beat a light coat of epoxy primer that is compatable with your topcoat system...others may have their opinion.

fixnflyguy said:

Some people choose to eliminate priming, and directly apply the paint topcoat, which I personally don't recommend. Its hard to beat a light coat of epoxy primer that is compatable with your topcoat system...others may have their opinion.

Click to expand...

I was assuming the OP meant bypassing priming for all interior substructure?
Not priming the exterior with a primer recommended for the paint being used is a very bad idea. The primer is an adhesion promoter. Today's paints don't adhere well without an appropriate substrate (primer) that it can cross link too.

Can you explain 'alodine applied as a controlled acid etch'? I thought the alumiprep was the acid etch, and the alodine was the conversion coating.

I agree with others that you probably have a cleaning issue. When I started my project, someone with a lot of experience told me to clean (degrease, mainly), rinse with *clean* water, acid etch, rinse with clean water, alodine, rinse with clean water. Using distilled water to rinse is best, but might cost more than the chemicals.

FWIW, the best cleaning technique I've found is to wipe any ink off with solvent, scuff with scotchbrite, & load the parts into a dishwasher, if they will fit. Run them through a full cycle using a good dishwasher detergent (excellent degreaser). Go straight from the dishwasher (using clean gloves) to the acid etch, and then through the rest of the steps.

Your wife will never know....

Charlie

fixnflyguy said:

So,
Not to start a "pre-primer" war, and following the process used by virtually all the major aircraft manufacture and repair process, (my day job), I will put into laymans terms the basics.
The aluminum as delivered is either "Alclad" ( most all sheet stock), or "bare", (most all extrusions). During the finish process of painting, the aluminum needs a good cleaning, either mechanical (Scothbrite,ect.) or chemical (Alumiprep,ect.). After cleaning, the Alodine is applied as controlled acid etch which seals and promotes adhesion for the yet to be applied primer/paint. Some people choose to eliminate priming, and directly apply the paint topcoat, which I personally don't recommend. Its hard to beat a light coat of epoxy primer that is compatable with your topcoat system...others may have their opinion.

Click to expand...

Absolutely spot on Bill. I would not eliminate the primer.

prime

You could clean and use self etch primer.
Bob

Pat Stewart said:

Absolutely spot on Bill. I would not eliminate the primer.

Click to expand...

One point here ... If you use Alodine - then do not use a etch primer .. use epoxy primer ... Etch primer (typical very light coat, almost translucent) to be applied on surface that has no other coating ... so it can etch into the metal ...

Show me your data report, I'll show you mine.

6 Gun said:

You could clean and use self etch primer.
Bob

Click to expand...

Where is your data that a self etch primer provides corrosion protection for 2024 in a salt spray booth with a scratch test.

BillL said:

Where is your data that a self etch primer provides corrosion protection for 2024 in a salt spray booth with a scratch test.

Click to expand...

Hi

It all depend on the etch primer you use ... http://www.paintservices.com/pr30b-etch-primer/

That etch primer is excellent alternative to Alodine. But may not be available in all parts of the world .. as it contain lots of not so nice stuff .. as far as your lungs are concerned ... But .. look at the standards it conforms to... Any other etch primer that conform to the same standards will works great as a primer against corrosion ...

Thanks everyone for the comments.

rvbuilder2002 said:

I was assuming the OP meant bypassing priming for all interior substructure?

Click to expand...

Yes I was only planning on the substructure. Haven't decided on whether to paint or "wrap" the outside yet...still a away off.

Thank you Bill, will take note of the cleaning.

BillL said:

Hi Ian,

Through some experimentation of my own, it appears to be a cleanliness issue.

I dip my parts, so let's start with that. I clean the parts with mineral spirits to get sticky stuff, and then wipe with a wet towel of alcohol. Denatured or rubbing (ethyl or isopropyl) all over. On small parts without label adhesive, acetone works too. I just don't like the smell. Dip in prep solution for 2-3 minutes, rinse in distilled water (sometimes just spray down small parts with hand sprayer), then dip in alodine for 2 1/2 minutes - or longer if weak to match colors. Rinse in new water, blow dry with shop air and hang for 24 hrs. That cured my mottling. Try these on your own for a starter.

Any other cleaning process you want to ask about - I probably tried it. Many worked but this seemed to must efficient and I stopped experimenting. Plastic buckets, 3" PVC tubes (vertical), and large plastic storage containers have been used.

Last thing - I had some corroded 2024 .063 and it looked pretty bad. It needed some scotchbrite to level the surface, then the other steps left a nice finish.

Click to expand...

JanRV6UK said:

Hi

It all depend on the etch primer you use ... http://www.paintservices.com/pr30b-etch-primer/

That etch primer is excellent alternative to Alodine. But may not be available in all parts of the world .. as it contain lots of not so nice stuff .. as far as your lungs are concerned ... But .. look at the standards it conforms to... Any other etch primer that conform to the same standards will works great as a primer against corrosion ...

Click to expand...

Fair enough, Jan. The tech data sheet looks like this is a what we would call a wash primer, and still needs a zinc/strontium chromate epoxy or urethane primer over it. Commonly in the US an etch primer is for automotive steel and does little or nothing for the 2024 aluminums. Too bad we (me) learn all the really good factual stuff at the end of the build! Maybe on the next one . . .

BillL said:

Fair enough, Jan. The tech data sheet looks like this is a what we would call a wash primer, and still needs a zinc/strontium chromate epoxy or urethane primer over it. Commonly in the US an etch primer is for automotive steel and does little or nothing for the 2024 aluminums. Too bad we (me) learn all the really good factual stuff at the end of the build! Maybe on the next one . . .

Click to expand...

Yep ... it is what I enjoy about this building stuff ... learning new things .. and hopefully not have to make to many parts in the process .... I think by the time I am done, I will have made 3 ... at least parts for 3 aircrafts !! ..

The primer I am using does contain chromate and does not need a separate epoxy primer - you are absolutely right that many generic etch primers are not suitable for aluminium and will require a top coat to seal it, and have no anti corrosion properties for aluminium. I could use this : PR 143 epoxy primer - from the same company - on top of the etch primer I am using now ... but I think that would at least for all interior be an overkill (and add more weight) - May do it on the outside, before top coat. Yes the etch primer is a wash primer .. very light coat ... but what is great about it .. as I said earlier it has anti corrosion properties and does not absorb moisture, hence no need to overcoat it ... unless you want ever better protection ....

Still very important to fully clean and degrease before you apply it (as is needed for Alodine as well) - In the US you tend to use Alumiprep 33 which is ideal to get the alu ready for etch priming (or Alodine) .. In Europe and the far east - maybe Australia as well ..?? This stuff is great DEOXIDINE 624 ... does the same as Alumiprep 33

No wonder they call it Primer war !! ... so many options ..!