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Alumiprep vs Prekote

Ender

Active Member
I have been doing the Prekote scrub + Akzo for a while now with good results. In looking to be more efficient, I’m wondering - What is the difference between etching with Alumiprep and scrubbing with Prekote.

Prekote is just a special chemical that thoroughly cleans the substrate, the 3m scrub makes it easier to bond the primer.

But isn’t that what an etch does as well? I’m wondering for all those small parts and flanges that are a pain to scrub, would the etch be enough?

I’m wondering if just doing the etch is good enough? I don’t live in salt water environment but I will continue to prime. I’m all for the epoxy primer because it holds up a little better when assembling compared to the etching zinc chromate aerosol options.

Thanks!
 
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I have been doing the Prekote scrub + Akzo for a while now with good results. In looking to be more efficient, I’m wondering - What is the difference between etching with Alumiprep and scrubbing with Prekote.

Prekote is just a special chemical that thoroughly cleans the substrate, the 3m scrub makes it easier to bond the primer.

But isn’t that what an etch does as well? I’m wondering for all those small parts and flanges that are a pain to scrub, would the etch be enough?

I’m wondering if just doing the etch is good enough? I don’t live in salt water environment but I will continue to prime. I’m all for the epoxy primer because it holds up a little better when assembling compared to the etching zinc chromate aerosol options.

Thanks!

An etch chemicaliy neutralizes/converts the outer layer of oxidized aluminum. It doesn't technically remove it and doesn't convert effectively like alodine. Scuffing creates a much stronger mechanical bond than a dead flat surface. I scuff with a detergent. Works quite well. A thorough scuff (i.e. 0 reflection) with a maroon pad will remove all oxidation, as well as create a stronger mechanical bond. The detergent helps to remove impurities, such as oil. Your prekote is doing something similar, but probably strongr and more effective. I should add that I clean the alum with laquer thinner before the scuff to help insure impurity removal. Years of parts sitting in the shop expose it to a lot of **** and don't want to drive it into the fresh surface with the pad

one problem with an etch, is the need for diligent rinsing/neutralizing; it is an acid. If you don't, it will create paint adhesion issues.

Larry
 
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Reviving a somewhat old thread.

I've been using Sherwin Williams fancy epoxy primer (got a good deal from work). Prep recommendation is Alumiprep and Alodine. Due to toxicity, I've been skipping the alodine on all but critical parts. Meaning scuff, Alumiprep, rinse, dry, prime. I've had great success with that. Sticks well, tolerates even dimpling afterwards and seems quite tough.

I'm considering switching to preKote. Sounds like a similar process; being scuff, preKote, rinse, dry, prime. Benefit is significantly less toxic and maybe better corrosion protection than Alumiprep only.

Important parts such as longerons will probably still get the full Alumiprep/Alodine treatment for chromate protection.

Is preKote better than just Alumiprep alone? How does it compare to the alumiprep/alodine process? Keep in mind this is going under epoxy primer on the interior.
 
Reviving a somewhat old thread.

I've been using Sherwin Williams fancy epoxy primer (got a good deal from work). Prep recommendation is Alumiprep and Alodine. Due to toxicity, I've been skipping the alodine on all but critical parts. Meaning scuff, Alumiprep, rinse, dry, prime. I've had great success with that. Sticks well, tolerates even dimpling afterwards and seems quite tough.

I'm considering switching to preKote. Sounds like a similar process; being scuff, preKote, rinse, dry, prime. Benefit is significantly less toxic and maybe better corrosion protection than Alumiprep only.

Important parts such as longerons will probably still get the full Alumiprep/Alodine treatment for chromate protection.

Is preKote better than just Alumiprep alone? How does it compare to the alumiprep/alodine process? Keep in mind this is going under epoxy primer on the interior.

Alumiprep nor prekote have any anti corrosion properties. Aluminprep removes aluminum oxides and the prekote is an adhesion promoter. Alumiprep cleans the oxides and if using Alodine combined it is adhesion promoter. Both methods should be used with 3M maroon pads for surface abrasion. Primers that are not specifically formulated with passivation elements included seal the surfaces, but do no stop corrosion from scratches with a passivating element.

All this is more important for copper alloys with high strength like 2024 aluminum. Adhesion quantification is done from peel testing, but corrosion is done with scratch tests.

Well adhered and non scratched paint does a good job of corrosion protection if the surface is clean under the paint (primers, prekote included). Paint is a system of surface, primer, top coat that should all be working together for adhesion and corrosion protection.
 
Alumiprep nor prekote have any anti corrosion properties. Aluminprep removes aluminum oxides and the prekote is an adhesion promoter. Alumiprep cleans the oxides and if using Alodine combined it is adhesion promoter.

I understand this to mean that I should use Alumiprep to clean, followed by preKote as the adhesion promoter? Alodine instead of preKote would be additional corrosion protection plus adhesion promoter with the downside of high toxicity.

The preKote website claims it is a cleaner and adhesion enhancer.

http://pantheonchemical.com/prekote-surface-pretreatment/
 
PreKote is listed as a cleaner but it’s not a very good one. I always wash with soap first then wash with PreKote two times. Works good. If your aluminum is kinda smutty looking (old and weathered) you can also wash with etch solution before the PreKote step.
 
Mechanical Vs. Chemical prep before Alodine

In the big plane world day job I work, structural repair manuals embrace either method, mechanical or chemical. I've done both more times than I can count, and unless I have a perfectly grease free part that I'm dipping in a chemical tank and a water rinse tank next to it, I go the mechanical etch..good old red scotchbrite, Dawn or your favorite dishsoap and a thorough scrubbing...you will not hurt the thickness of the Alclad. This will almost always yield a "break free" water test when done, and then a quick application of Alodine. If your working with Alclad thats going to be polished, just avoid that surface and scrub the backside. Easy, no harsh chemicals and fast. Also, you can do assemblies that are riveted together, and not have to worry about the acid etch trapped in the faying surfaces.
 
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