Proper use of Alodine

I have a 12' aluminum van roof rack that I want to paint.  I think I have all the steps ready in my head, but I'm terrible when it comes to paint and body stuff.

First thing I did was go over the whole thing with a wire wheel and cup on a grinder to get all the oxidation off and give it some tooth.  I bought some C-IC 33 (brightener/cleaner) and some MC1201 chromate and I understand how to dilute and use.

First question is:  It warns against letting either of those two dry during application and the 2-5 minutes of active time.  Should I split it up into sections and treat each piece separately?  I'm afraid that it will take more than 2-5 minutes to apply on the whole thing, meaning that by the time I'm ready to spray it off, the first spot I applied will be in danger of drying, and the last spot will only have 30 seconds before I rinse

Second question is:  The directions say something like "paint soon before dirt and corrosion can re-form."  Does that mean within a few hours?  Or does that mean a month?  I'll be doing this under a roof, but outside so I kinda have to wait for the right day.

Third question is:  Is there a preferred paint chemistry that does better with aluminum?  I'm told I need an etching primer (makes sense) but what "system" should I use?  I ask that both as a paint noob and for what works best on aluminum.

I've never done anything the size of a van roof but the procedure for individual components at the shop was always:

Wash with water, scrub with Alumiprep (I suspect this is your C-IC 33) let sit for recommended dwell time (can't remember specifics), wash with water.

Dunk part in Alodine tank and remove, let dwell for recommended time, wash with water.

Air dry with blow gun.

Paint same day.

Right before paint we wiped the parts down with MEK and a clean, lint free cloth. Next step was light shot of etching primer and then paint.

The Alumiprep or Alodine processes are surface etching so I wouldn't use an etching primer after it.  I would use a zinc chromate primer after Alodine.

If you've ever welded aluminum you already know that aluminum starts forming an oxide layer almost immediately so paint as soon as possible.

Alodine can also be brushed on, just keep the surface wet for the recommended time.

Short-ish answer to 1st question: do both steps in small sections.  You absolutely do not want either the cleaner or the Alodine to dry on the surface before rinsing, and rushing the processing time for either step makes it that much less effective.

Short-ish answer to 2nd question: NASA sez: "For any primer or bonding to have adequate adhesion, it is important that the primer or adhesive be applied in less than 48 hours after the conversion coating process is performed." A YT comment sez no less than 12hrs and no more than 72hrs b/c it caused adhesion problems.

Short-ish answer to 3rd question: I have no comment about topcoats, but do NOT use etching primer over chemfilm.  Etch primer needs to come into direct contact with bare metal.  Chemfilm makes sure that the primer does NOT come into direct contact with bare metal.  Reference1, Reference2, Reference3, Reference4 

Personally, instead of messing with chemfilm, I would be more inclined to spend extra time on mechanical surface prep, and then look for a truly righteous self-etching primer (like 2-part or whatever).  I will admit that I did use a Touch-n-Prep pen (like a Sharpie Magnum but filled with Alodine fluid) before painting to stop the bead corrosion on a couple aluminum wheels, but that was really only b/c I had one which was past its expiration date.

Other comments (I had typed up a whole buncha stuff for last time but never finished it or posted.  I do this fairly often.)

• remember that M-CR 1201 is Type 1 with hexavalent chromium (i.e. the nastier stuff, leaves a gold colored coating, may still work better than Type 2).  M-CR 1001 is Type 2 with trivalent chromium (i.e. the less-nasty stuff, leaves a 'clear' coating).  Both contain chromic acid.  Don't get it on any of your body parts.

• chemfilm needs to be applied to a perfectly clean and absolutely bare aluminum surface.  No remains of previous anodize.  No atmospheric oxidation (the kind that forms semi-instantly when exposed to air).  No nothing except aluminum atoms.  The phrase is "water break free" meaning that rinse water simply sheets off the surface.

• Alumiprep and Alodine are completely different things, and are used for completely different purposes.  Alumiprep (and Alumibrite) are acid solutions which remove undesirable stuff off the aluminum surface.  Alodine (a.k.a. Iridite, chem film, chromate conversion coating... whatever) creates a very thin gel coating on top of the metal surface.  Contains chromium and other stuff, somewhat self-healing, electrically conductive, etc.

Misread title. I'm such a child.  This is all I can think of.  
 

"do you want the Aladeen news or the aladeen news?"

In reply to Oapfu :

The surface prep is done, although it has been a while. I used a steel wire wheel and cup on a grinder and there was no pitting to start with.  So you're thinking maybe another soapy bath with a heavy scotch brite to lift the oxidation that has grown for the last few months, then MEK, then etching primer?  Reading Bonderite's stuff it says that the C-IC brightener removes oxidation.  Maybe do the brightener step but not the chromate step?  I think I'm asking... do I need to re-prep mechanically, or with the Alumiprep?  The main goal here is to change the color with paint and be durable when loading lumber, pipe, etc.  It's a roof rack, so it doesn't need to perfect... which is good because my skills with a sprayer are pretty lame.

Taking from that experience you listed above, looks like my window is 12-48 hours.  I can deal with that.

ShawnG said:

I've never done anything the size of a van roof but the procedure for individual components at the shop was always:

Wash with water, scrub with Alumiprep (I suspect this is your C-IC 33) let sit for recommended dwell time (can't remember specifics), wash with water.

Dunk part in Alodine tank and remove, let dwell for recommended time, wash with water.

Air dry with blow gun.

Paint same day.

Right before paint we wiped the parts down with MEK and a clean, lint free cloth. Next step was light shot of etching primer and then paint.

Dunk would be great, but I have a quart of each chemical and a 12' long pieces.  I can't imagine that being feasible.

Alodine is not something I recommend, endorse, or see much value in as a DIY process. Not only is it toxic to you if handled improperly, but the toxic wastewater will also contaminate downstream sources for others if not also disposed of properly. 

Since you're asking about doing Alodine "properly", please ensure you're taking the time and effort to handle and dispose of it properly too.

Driven5 said:

Alodine is not something I recommend, endorse, or see much value in as a DIY process. Not only is it toxic to you if handled improperly, but the toxic wastewater will also contaminate downstream sources for others if not also disposed of properly. 

Since you're asking about doing Alodine "properly", please ensure you're taking the time and effort to handle and dispose of it properly too.

Solid advice

Here is what the surface looks like now.  I did this in the spring, so I'm sure it has oxidized enough that something needs to be done.  Alumiprep, or more mechanical scrubbing?

I just checked this. You bet it has already oxidized. Scotch Brite or 320 grit wet or dry paper used wet. Alumibrite if you must, but not needed if you rinse your wet sanded pieces and air blow dry them, then paint with self etching primer within an hour. Color coat after the time the primer specs. I use an Axalta product called Variprime, but it is not sold in small enough quantities for your single rack. I think Eastwood has a similar and compatible product in spray cans. Every automotive paint supplier has the right product, but they sell a whole quart as a minimum, and you need far less.

I realize I'm probably overthinking this, but my thought with the alumiprep (the c-ic 33) was that I now have a very rough surface.  320 grit or scotch brite would scrub the peaks but not the valleys while the prep would soak in and do a deeper clean.  The c-ic 33 instructions say apply, scrub any heavily oxidized areas (which I dont' have), let sit for 2-5 min, rinse, dry, paint.  I'm just wondering why that would be better/worse than 320... especially given the curves and cavities of the shape of the rails.

May I ask what you believe is so beneficial about Alodine for your application, that you feel the need to use it over other widely accepted, easier, and safer protective finishes? Especially when talking DIY. If it really is that critical for it to specifically be Alodine treated, then it's probably worth having it done by a professional finishing shop that already has the proper equipment and experience to ensure it's done correctly.

To me this comes across a bit like when somebody asks how to DIY a structurally bonded aluminum monocoque chassis for a Locost, rather than just welding up a steel tube frame. If you have to ask...

Driven5 said:

May I ask what you believe is so beneficial about Alodine for your application, that you feel the need to use (DIY) it over other widely accepted, easier, and safer protective finishes? If it really is that critical for it to specifically be Alodine treated, then it's probably worth having it done by a professional finishing shop that already has the proper equipment and experience to ensure it's done correctly.

While alodine isn't necessary it does aid in paint adhesion and slows corrosion.

In reply to triumph7 :

So does primer.

Driven5 said:

May I ask what you believe is so beneficial about Alodine for your application, that you feel the need to use it over other widely accepted, easier, and safer protective finishes? Especially when talking DIY. If it really is that critical for it to specifically be Alodine treated, then it's probably worth having it done by a professional finishing shop that already has the proper equipment and experience to ensure it's done correctly.

To me this comes across a bit like when somebody asks how to DIY a structurally bonded aluminum monocoque chassis for a Locost, rather than just welding up a steel tube frame. If you have to ask...

Nothing about my request is anything like building a max-effort Locost chassis that a mistake means life or death.  I'm asking how to paint gooder.  It's the equivalent of asking what car wash soap to use on my Locost.

I'm simply asking questions and trying to understand the chemistry behind the answers so I can make informed decisions which will lead to the paint sticking better.

Why I believe alodine is better?  First... I don't know that I do.  Which is why I asked in the previous thread and ended up purchasing some one the recommendation of a few folks.  What I do know is that I can't just rattle-can bare aluminum and expect it to stick.  The C-IC 33 is described as "goes deep into aluminum pores and removes oxidation and contaminants."  The 1201 is a chromate conversion coating which aids in paint adhesion.  I've learned from this thread that etching primer is designed to do the same thing as 1201, so I can skip the chromate conversion if I use etching primer.  Great.

I've moved on to asking if it's better to C-IC 33 to prep for the etching primer, or if mechanical sanding is better... and WHY.  In my brain, it seems like sanding the peaks of the rough finish for two hours will leave oxidation in the valleys, whereas using the C-IC will be a deeper prep.  If you have reasons why one is better than the other, please share them.  I will say that spraying some liquid is a LOT easier than mechanically sanding about 65 feet worth of intricately-shaped aluminum extrusions.

I have used alodine before, but it was in a much smaller application.  I had a painted aluminum boat that I wanted to re-spray.  I sanded it out and used alodine on any places where it had sanded through or had been chipped off by a rock.  It wasn't rocket surgery, and I was only 16 and was able to figure it out, but it was also 20 spots that were about the size of a quarter.  I was just following instructions.  This time I want to learn WHY from people with more experience.

I have the chemicals.  I have scotchbrite pads.  I have 320 grit.  I have a hose.  I'm simply asking for opinions from experience.

In reply to Curtis73 (Forum Supporter) :

That's kind of my point. I'm not sure what previous thread, but IMO Alodine is a material for max-effort life or death type applications while a roof rack just needs a good 'soap'.

Also my apologies for the additional Alodine comments. While I had seen additional asks about SE primer, I didn't see anything about actually having changed direction.

Here's a little primer on some types of 'soap' to use:

https://www.autorepairsdirect.com.au/blog/differences-between-epoxy-primer-and-self-etch-primer-for-bare-metal

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjp_POs6vOAAxUwADQIHWJrDn4QFnoECA8QAQ&url=https%3A%2F%2Fwww.tat-co.com%2FTranstarAutobodyTechnologies%2Fmedia%2FTATCo%2FTechnical%2520Tips%2Ftranstar_techtip_EpoxyBareAluminumTip105.pdf%3Fext%3D.pdf&usg=AOvVaw3H5XabCfwYF2rT4niF9G64&opi=89978449

As I understand it, traditional SE primer is porous and lets water through if gets exposed by any paint damage. Probably not great for the way a roof rack gets beat up. An epoxy, or DTM, primer with some light sanding/scuffing of the aluminum is the direction I'd probably be leaning. The handfull of DTM/epoxy primer instructions I can recall seemed to simply be asking for freshly abraded bare metal, and didn't actually reference an etching option. Without being a finishing expert, I'd fall back on the primer manufacturer recommendations for maximizing adhesion.

Then again, I am somewhat biased. For DIY I'll defer to the greater physical effort over the greater physical effects of chemicals any time I reasonably can.

Random thought... Have you considered bedliner?

In reply to Driven5 :

Gotcha.  Thanks for the reply.

I did consider some kind of other coating.  Powdercoating is always a [stupendously expensive] option.  Best quote I got was $1800 if I did all the prep and then it came with no warranty.  Bedliner crossed my mind, but I'm going for a pretty specific color.  Triple Bronze to be exact.  The other reason bedliner is not a wise option for me is that this rack is all made from t-slot aluminum with pretty tight tolerances.  Since it will be used for contractor-type work during the week and off-grid, rooftop camping on the weekend, maintaining the smoothness of the t-slots is pretty critical.

Driven5 said:

In reply to triumph7 :

So does primer.

When I worked with it we did alodine, primer (non-etching) then paint.