Alodine questions

[findane]

After reviewing several threads regarding Alodine priming I still have some questions. Apparently, priming with Alodine is not as simple as soaking the part in a tub or is it. Must the part be prepped with Alumaprep? Is the Alodine alone sufficient for corrosion protection or is it necessary to also prime. What are the proper steps for using Alodine.

I used the 7220 rattle can primer on the empannage. Easy to use but expensive. The wings have a whole lot more priming than the empannage.

[JanRV6UK]

Alodine on its own add zero weight and is an excellent corrosion treatment – and yes all you have to do is to stick the bits in a tub of nasty chemicals - i.e. do not drink the stuff of put your hands in it .. !  ...

BUT.. unless the parts are ‘washed’ (cleaned) with Alumiprep – Alodine will not stick ... and NEVER touch the Alumiprep treated surface with your bear hands – sweat from your hands will also contaminate the surface and Alodine will not stick ..

I assume you are in Florida .. so nice and warm ... So the drill would be ...

Not is direct sunlight but nice and warm .. get a couple of high density sheets of blue polystyrene – use them as working surface for cleaning the aluminium parts with Alumiprep and fine Scotch bright grade 7447 - Then with a hose pipe you rinse each part .. the water should sheet off .. its easy to see the difference but a bit hard to explain ... that show that the alu is clean and ready for Alodine ... then suspend the part in the Alodine .. depending on how strong your solution is ... 2 or 3 minutes ... lift out (it will have a light golden colour .. almost like Anodizing .. rinse off ... then leave to dry ... the surface does scratch easy ... takes a day or so to go harder ....

Rattle can is a lot easier and less messy ..... I still would recommend the Alumiprep to ensure the aluminium is really clean ..

Oh ... ‘clean’ in this contexts is = No grease No oxidisation ... (i.e. the water will ‘sheet off’ ....)

So many ways to ‘prime’ ... no wonder they call it the primer war !!:-)

[fixnflyguy]

Welcome to aluminum finish 101..To make it simple and sweet, Alodine is a conversion coating etch that best prepares aluminum for adhesion of primer, which is what the paint sticks to.
Step 1) Clean the aluminum chemically(Alumiprep,ect.) or mechanically (Scotchbrite,ect.), then wash.
Step 2) Alodine conversion coating, water rinse and dry. You can brush,wipe, spray, or immerse to apply. If immersing, a bag with minimum amount can be used. Alodine only takes a few minutes to do its job, then needs rinsed.
Step3) Prime only with a primer compatable with the selected topcoat paint.
Because this is laymans basics, there are details to know about each process you need to become familiar with. many will advise/comment, but my personal advise is, if your not going to do the paint work, only focus on the inside skin/parts and let the paint shop handle the outside. The spray can primer wont help the painter..he will strip it off.
Step 4) Paint and enjoy.

[spark68]

Alodine is not too hard to do. EAA has a good video on technique.

http://www.eaavideo.org/video.aspx?v=1340416082001

[rv7charlie]

And, not to pick nits, but alodine doesn't 'stick' to the aluminum; it *converts* a microscopic top level of the aluminum to... shucks, I don't know what, but it's a chemical alteration of the surface so that it won't corrode. If I understand the concept, it's basically 'corroding' (converting) the surface aluminum to an oxide that will not corrode further.

https://en.wikipedia.org/wiki/Conversion_coating

If there is dirt, oil (including from your skin), or other contaminate on the surface (including the naturally occurring surface corrosion on the alclad), the alodine can't get to the surface to do its job. [EDIT: If the surface isn't clean, the alumiprep can't do it's job, either, so clean first.] That's the reason for clean/degrease, rinse, acid etch (alumiprep, which removes the skin of corrosion), rinse (to be sure all the acid is gone), then dip in the alodine solution for the recommended time period, rinse again (to stop the conversion process).

Do NOT attempt to do the alodine step outside (or even in front of a window). Sunlight neutralizes the alodine fairly quickly. Then you get to buy more alodine. It will last a long time and can be reused, if kept in the dark, and clean.

BTW, a dishwasher & regular old dishwasher detergent will probably do a better job of cleaning/degreasing than any manual process you try.

Charlie

[wilddog]

If you alodine the exterior before painting, how do you keep the Alumiprep and alodine out of the overlaps in the aluminum skins?

[BillL]

Peter, I hope flying and birdwatching are separate activities

As a new poster, you can use "site:vansairforce.com term1 term2" in google as a site search term. It will list all the threads with the search terms listed.

There are some good discussions on alodine elsewhere on VAF. You might do a little experimentation to settle on your process, some here are not wrong, but leave out steps that affect results for brevity. Acetone and alcohols (pick one) will pre-clean, various formulations of alumiprep will remove oxides, I dip for 2-3 min, rinse in distilled water, then dip in alodine 3+ min, then rinse with distilled again. Lightly blow dry catching the yellow drips with a towel and dispose. Hang small parts with stainless safety wire. Many successful variations of this. With relatively clean aluminum to start with, no mechanical (sanding etc) roughing is needed (based on limited testing).

I made dipping tanks of 3" X 24" PVC and added rubber caps for the tops to seal them. I tried two dipping tubes for rinse, but usually resort to a spray bottle of distilled water, catching the run off as scum was forming in rinse water. Large parts are done in rubbermaid storage containers with several gallons. Sometimes a double dip is needed to get both ends of a part. I have no experience with larger parts or with already riveted joints.

Alodine dip times will change as it becomes depleted. I usually discard when 5-7 min fails to yield a good color. Color also varies with alloy from part to part.

Shop limitations vary, but for me, alodine is better than small batches of primer and it is documented to be a significant corrosion inhibiter.

Have some fun with experimentation to yield a good series of parts, and "your" process.

[rv7charlie]

Originally Posted by wilddog

If you alodine the exterior before painting, how do you keep the Alumiprep and alodine out of the overlaps in the aluminum skins?

One way is to alodine the skins before assembly. I confess that I didn't do it, because I was too lazy to set up an elaborate system to catch overspray (a pump-up sprayer to keep the surface continuously wet for the required time).

Having said that, years ago when visiting a friend who'd just finished building his 2nd RV, I watched some of his friends who were prepping his plane for paint. They had washed it, & were rubbing it down with scotchbrite & alumiprep. He said they'd painted numerous planes the same way, & just rinsed thoroughly between steps, same as individual parts. Haven't seen the plane since, so I can't say what the long term effects were.

Years later, I heard a couple of other tips. One is to buy powder instead of liquid alodine (much cheaper and can be stored until needed). Another is that if you buy the powder, you can afford large batches. The suggestion was to mix it in a very large plastic garbage can or barrel with removable lid. That way, you can coil the skins & dip like you would the smaller parts. I've been told (but haven't verified) that as long as you keep it away from light, it will last a long time in a garbage can or barrel.

[rv7charlie]

Originally Posted by wilddog

If you alodine the exterior before painting, how do you keep the Alumiprep and alodine out of the overlaps in the aluminum skins?

One way is to alodine the skins before assembly. I confess that I didn't do it, because I was too lazy to set up an elaborate system to catch overspray (a pump-up sprayer to keep the surface continuously wet for the required time).

Having said that, years ago when visiting a friend who'd just finished building his 2nd RV, I watched some of his friends who were prepping his plane for paint. They had washed it, & were rubbing it down with scotchbrite & alumiprep. He said they'd painted numerous planes the same way, & just rinsed thoroughly between steps, same as individual parts. Haven't seen the plane since, so I can't say what the long term effects were.

Years later, I heard a couple of other tips. One is to buy powder instead of liquid alodine (much cheaper and can be stored until needed). Another is that if you buy the powder, you can afford large batches. The suggestion was to mix it in a very large plastic garbage can or barrel with removable lid. That way, you can coil the skins & dip like you would the smaller parts. I've been told (but haven't verified) that as long as you keep it away from light, it will last a long time in a garbage can or barrel.

[findane]

Thanks to all for clarifying the application of Alodine. The information is a great help. Looks like I need to get some Alumaprep. Anyone have a suggestion for purchasing Alumaprep or the powdered Alodine?