Something I just dont get ....

Post by **Spike** » Tue Nov 30, 2004 7:28 am

I'm currently doing research concerning priming, etc, to see where I fall in respect to current practices. I'm leaning towards alodining my parts and then using a self etching primer only where parts or sub assemblies are touching/joined. I probably wont prime alodined parts either where they are not comming in contact with other parts.

So here is what I dont get. We spend lots of money for 2024 alclad aluminum. Why is it that the first thing we do when we prep parts for the alodine is to scrub off the alclad layer? Its typically done so that the alodine will have something to grab onto. But why pull off one corrosion protection just to replace it with another? Seems to me that we should just dunk the parts and let the alodine worry about where we have scratched or worked on the parts.

Educate me please.

-- John

captain_john · Post by **captain_john** » Tue Nov 30, 2004 4:02 pm

Well, you are not removing the alclad. The alclad coating is normally up to 5% of the total thickness of the material. What you are doing is creating an "adhesion profile" when you scuff it up for preparation. This allwos the primer to get a better "bite" if you will, onto the material.

How is that? Does it help?

CJ

Post by **Spike** » Tue Nov 30, 2004 4:11 pm

Using those numbers if your scuffing up .032 aluminum, the alclad is only .0016 thick. If thats true I dont see how you can scrub the parts down with an acid based cleaner and a scotchbrite and not remove the alclad.

-- John

captain_john · Post by **captain_john** » Tue Nov 30, 2004 5:17 pm

Well... methinks you are doing more scrubbing than scuffing?

All you need is an adhesion profile. Don't try and remove an even layer of material. A light touch is all that is needed.

My schotchbrite pads don't have any gauges on them, they aren't that precise. The concept is to just put an uneven, randomized surface to the metal before the application of the coating.

CJ

Thermos · Post by **Thermos** » Tue Nov 30, 2004 5:51 pm

For what it's worth, I started out as a 'primer zealot.' I alodined all my HS and VS skeleton parts and skin interiors, and then primed same with a quality (read 'expensive') epoxy primer. It was a pain in the butt - I hate using toxic chemicals.

That initial experience caused me to reconsider what I really needed to do. One thing that helped was observing where I have corrosion in our Archer and where I've seen it on other, similar airplanes. I came to the same conclusion as you - corrosion is most likely where moisture gets trapped or is allowed to stand. So that's where I'm scuffing, alodining, and priming alclad parts. Everywhere else will just be protected by the alclad itself.

Speaking of alclad, I think Van's spreads a little misinformation about the ease with which it's removed. After reading CJ's posts, I pulled out my feeler gauges and looked at the 0.002" gauge. It's thicker than I would've guessed, and I don't think mild-to-moderate scuffing would remove that much material. And the phosphoric acid in Alumiprep is so dilute that I doubt it would remove much material, either.

Thoughts?

Dave

Thermos · Post by **Thermos** » Tue Nov 30, 2004 5:58 pm

One other comment about alodining. If you use alodine but don't plan on treating everything, take a look at Touch-n-Prep pens. Essentially a big magic marker of Alodine 1132. Dries in place, no rinsing necessary. I use one, works great!

Dave

Post by **Spike** » Tue Nov 30, 2004 10:18 pm

Thermos wrote:One other comment about alodining. If you use alodine but don't plan on treating everything, take a look at Touch-n-Prep pens. Essentially a big magic marker of Alodine 1132. Dries in place, no rinsing necessary. I use one, works great!

Dave

I havent started prepping yet at all. Right now Im just doing a bit of research for when I make a decision. I think that right now Im leaning towards alodining without doing the aluminprep & scuffing stage. Alternatively I could use that pen, it sounds nifty. Then Ill use a self etching primer only where I have parts touching / fastened together. At least thats the plan at this hour.

-- John

mustang · Post by **mustang** » Mon Dec 06, 2004 3:24 am

I have a friend who is currently building his 6th RV. He recommended the self etching primer sold at Lordco here in Canada. This is a rattle can of grey colored primer. I bought 3 cans a while ago but I have not tried it on aluminum.

Today I was changing wheels on my Mustang (car) over to winter tires with aluminum wheels. I pulled one of the calipers on the back that was a bit noisy to inspect the pads. Everything was OK so I pulled off the disc to use my handy dandy 3 inch scotchbrite roloc buffer from Avery and cleaned off the rusty center section. I then cleaned the flat surface with brake cleaner and shook up spray the can, thinking, I won't bother masking, I'll just shoot this freehand and wipe off any overspray on the disc with brake cleaner later. That is what I did and put the disc on a warm baseboard heater to dry. Ten minutes later I sprayed the friction surface of the disc to wipe off the overspray and...... guess what? NOTHING WIPED OFF! Brake cleaner would not touch this primer. Furthermore, this dirt cheap primer stuck like "you know what" to a blanket! I had to grind it off with the scotchbrite roloc wheel.

I have to say that I am impressed. I'm gonna try a test shoot on a piece of aluminum tomorrow. I'll report further.

Cheers, Pete

Snap · Post by **Snap** » Mon Dec 06, 2004 6:03 am

this sounds interesting. I will be waiting for the results. I wonder if I can get that stuff here in Australia?

Post by **Spike** » Mon Dec 06, 2004 10:00 am

Ditto that. Care to try and sneak some through UPS ?

RV6junkie · Post by **RV6junkie** » Mon Dec 06, 2004 10:41 am

I hate to start a flame war....but I will if I have to...

Most people tend to go overboard with priming. Way overboard.

The reason we use alclad aluminum is because it is corrosion resistant. There really isn’t any reason to prime the interior surface of every skin inside the aircraft. The only exception I can think of is the cockpit area because of the high traffic this area sees over the lifetime of the aircraft.

When I think back to the hours and money wasted, not to mention the toxic chemicals I exposed myself to, I doubt if it was worth the effort. I was one of those people that primed everything…twice. I must have added several pounds of primer to the tail of my RV. I continued to prime everything in sight as I riveted the wings together. But by the time I got done with the control surfaces I began to see the light. I only primed the rivet lines that I drilled into the skin; and a light coating at that. I continued this procedure for the remainder of the airplane.

10 to 15 years later (depending on the parts) guess what…no corrosion. None. Anywhere. And I live in the epicenter of acid rain and salt water. Now, my RV has spent its life in a hangar, but that just keeps direct rain off the aircraft. My hanger is as damp as a foggy morning. Not only that, the aircraft spends many weekends tied down at the beach. So if anyone is going to see corrosion, its me.

All of the alclad surfaces are as shinny as when I pulled the blue plastic off so many years ago. Will my aircraft last 100 years? I don’t know. I know that I wont!

Prime less, build more.

Post by **Spike** » Mon Dec 06, 2004 10:49 am

Here Here. Junkie for President!!!

-- John

4kilo · Post by **4kilo** » Mon Dec 06, 2004 11:58 am

RV6junkie,

Where are you located? East or west coast? When I ever finish my RV it will probably spend a lot of time on the coast of South Carolina, so your location and experiences are quite relevent to me.

Thanks,

Pat

Snap · Post by **Snap** » Mon Dec 06, 2004 8:21 pm

I second the motion. (all hail pres rv6junkie)

I only ever intend on Priming the parts that I touch, scratch or have worked on. Think 'lots of prime lines over aircraft'.
If it is metal on metal, Prime. Thats it. No more than that.

RV6junkie · Post by **RV6junkie** » Mon Dec 06, 2004 10:40 pm

4kilo wrote:RV6junkie,

Where are you located? East or west coast? When I ever finish my RV it will probably spend a lot of time on the coast of South Carolina, so your location and experiences are quite relevent to me.

Thanks,

Pat

NJ

728GD · Post by **728GD** » Tue Dec 07, 2004 11:36 am

I have to agree with RV6junkie. When I started building my 6 I alodined tail feathers. After spending countless hours preping and figuring out a way to coat the larger pieces, I started to remember what my '46 C140 looked like inside. You know, in the tail cone, inside the wings..... It was perfect. No primer, no alodine, no nothing. I quit trying to alodine. I did prime, but I did it lightly. Most builders I have seen spray way too much primer. I don't even know if I would prime everything any more. When I built, there was no protective cover on the skins, heck, I had to drill out the lighting holes on the wing ribs!!! If my old C140 could live for 58 years with no primer or alodine, lets see, I will be 101 years old when my RV reaches that point. Just take care at dis-similar conection points and the tail cone area if building a tail wheel.

papakeith · Post by **papakeith** » Thu Feb 23, 2006 3:15 pm

I have to bounce this one to the top.

you see, rv6junkie is the guy responsible for getting me to start thinking of building my own plane.

Why just today I was talking to him about building. He said something along the lines of, " These days, it's just dimple, countersink, cleco and rivet."
I chimed in with , " you forgot prime".

he responded, "forget about priming, and you better not mention alodine to me either!"

Then I found this thread. I guess he hasn't changed his opinion much since 2004

johnk · Post by **johnk** » Thu Feb 23, 2006 6:31 pm

I also think that the alclad is harder to "scrub" or "scuff" off than we might think. When I scuff before priming, the scuffing doesn't even remove the sharpie marks, it just dulls them along with the aluminum surface. It's hard to imagine that I'm scrubbing right through to the alloy.

John