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-   -   Alodine vs. SEM rattle can (https://vansairforce.net/community/showthread.php?t=146170)

dirtybirdy80 01-29-2017 02:07 PM

Alodine vs. SEM rattle can
 
I searched the forum and couldn't find an exact answer for my question. I know corrosion protection is a hot topic and age old debate, but here is my question....

I live out in Santa Rosa, CA (KSTS). In the summer its typically bone dry, but its rainy in the winter and we get coastal fog in the evening and morning, so there is moisture in the air at times.

Therefore, I definitely want some form of protection from corrosion. I'm looking for simplicity, durability, and light weight. My two thoughts were...

1. Cleaning the aluminum with mineral spirits or paint thinner and using SEM self etching rattle can primer.

2. Brushing on Alumiprep 33 followed by brushing on Alodine 1201.

I don't want to do both, just to keep the weight down and the cost down.

Any information is greatly appreciated.

N427EF 01-29-2017 02:57 PM

Over in Concord KCCR
 
Quote:

1. Cleaning the aluminum with mineral spirits or paint thinner and using SEM self etching rattle can primer.
That was my choice for the same reasons you mentioned, simplicity and also
effectiveness.
My choice for cleaning was acetone, never had an issue with primer.
Large parts would get a thorough cleaning with 409 water solution using a pink scotch brite pad before a final wipedown using acetone. 409 has a slight etching effect on aluminum as well as excellent grease solving qualities.
I used this method for all my interior parts but resorted to an edge and alodine prep for the final exterior paint job.

I noticed in an earlier thread that the poster was applying multiple coats of self edge primer. One coat is all it takes, keep it simple and self etch rattle can SEM will do just that for you.

BillL 01-29-2017 03:46 PM

I went with alodine vs spray for small parts. I am lazy.
 
For small parts or ones that will fit in a 10 gallon rubbermaid storage container, I use alodine rather than straight primer. A primer has several functions, base coat for adhesion of upper layers, active corrosion retarding due to active ingredients, and/or corrosion prevention by barrier. The Mil Spec test use a scratch test. DoD testing showed that alodine alone was equal to just a light coat of chromate primer, a washcoat. So ,I used this method after learning. The time delay between application and installation is reduced and the dimensional changes are nil w/alodine. Also very few rattle cans have zinc or strontium chromate. Neither of which I want to spray indoors anyway.

I don't know why I care anyway this plane will outlast me by a decade, no matter where is is located. Alodine parts just look cool.

Gisnar 01-30-2017 11:19 AM

How does zinc phosphate primer (available in rattle can) compare to zinc chromate? Is it at least less toxic?

rv7charlie 01-30-2017 12:04 PM

Years ago, a friend who lives ~30 miles from the ocean did a test with 2024 tabs treated with pretty much every combination you could dream up, from bare to alodine to all manner of chromate and epoxy coatings. The tabs were wedged into slots in a 2x4, & dipped in a bucket of sea water every few days, & left lying across the top of the bucket the rest of the time. The alodined sample survived as well as the most elaborate treatment.

But know that you can't 'brush on' the acid etch and then 'brush on' the alodine. Yes, you can use a brush, but you still have to clean properly first, treat for the proper time frame in each step, and rinse properly between and after each step.

Charlie

BillL 01-30-2017 12:12 PM

Quote:

Originally Posted by rv7charlie (Post 1146124)
Years ago, a friend who lives ~30 miles from the ocean did a test with 2024 tabs treated with pretty much every combination you could dream up, from bare to alodine to all manner of chromate and epoxy coatings. The tabs were wedged into slots in a 2x4, & dipped in a bucket of sea water every few days, & left lying across the top of the bucket the rest of the time. The alodined sample survived as well as the most elaborate treatment.

But know that you can't 'brush on' the acid etch and then 'brush on' the alodine. Yes, you can use a brush, but you still have to clean properly first, treat for the proper time frame in each step, and rinse properly between and after each step.

Charlie

Yep, also says the European Space Agency. If you want all the test data, chromates, non-chromates alodine only etc. Salt spray cabinets, fence exposure for years, and the like send me your email by email/pm, not pm. I will send a copy of all my primer documentation generated by many tax dollars. Lots of DATA. Read all this and you will be a primer expert. If you don't, you will believe the TV program Scorpion is all real and based on science.

dirtybirdy80 01-30-2017 04:05 PM

Thanks for the response. Think I'm going to keep it simple and light weight and go with Alumiprep, followed by Alodine.

Oliver 02-20-2017 07:51 PM

Quote:

Originally Posted by dirtybirdy80 (Post 1146201)
Thanks for the response. Think I'm going to keep it simple and light weight and go with Alumiprep, followed by Alodine.

Keep in mind, though, that while the Alodine treatment is simple, you are not allowed to let any left over Alodine or water contaminated with it, into the sewer system - IMHO impossible in a hobbyist shop.

This alone was reason enough for me to not use Alodine. Getting caught might result in a VERY expensive learning experience...

We prepared all components of the tail feathers with Prekote and then primed them with Stewart EkoPoxy. This is however quite a bit of work - for the tailcone we will probably apply self etching primer, with a 2" wide foam paint roller, to the contact surfaces.

David Paule 02-20-2017 07:56 PM

Quote:

Originally Posted by Gisnar (Post 1146106)
How does zinc phosphate primer (available in rattle can) compare to zinc chromate? Is it at least less toxic?

I've used Moeller zinc chromate primer in rattle cans. Frankly, it's a poor paint, or at least a poor rattle can sprayer, at least compared to SEM. SEM's a very good paint but doesn't have a chemical corrosion preventive, as far as I know. It's just a barrier primer, intended to be top-coated.

Dave

Oliver 02-20-2017 08:05 PM

Quote:

Originally Posted by David Paule (Post 1151777)
I've used Moeller zinc chromate primer in rattle cans. Frankly, it's a poor paint, or at least a poor rattle can sprayer, at least compared to SEM. [...]

I'm looking at the PTI Zinc Chromate self etching primer, which comes in different sizes and colors. Not cheap, though, and I don't have personal experience with it yet:

https://www.aircraftspruce.com/pages...ptiprimers.php


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