The madness has struck another...

I just received my emp kit... like most, I've never built a plane before but I'm already having a blast and I haven't even finished inventorying the kit yet. This is the world's best jig saw puzzle!

Someday it is going to be an 8A, FP prop and ~180HP engine, ground adjustable pedals, eletric trims (and flaps) on the stick, and I'm of two minds on rear pedals...I'd like them in theory but I'm not sure they'll be worth the cost ($$, weight, and build time). I have plenty of time to dither about those details though.

I do have a process question about building this beast. I have AKZO primer and am going to go through the whole MEK/Metal Prep/Alodine/AKZO cycle on the parts I prime. I did this on the "Study Project" and decided I really didn't like the smell of most of the chemicals, so I'd like to prep everything and do all of the priming in one pass. OK, it wasn't only the smell, but you get the idea. Any views on the best way to do this? Or is it even a worthwhile approach?

Have fun,
Jon

Priming in one pass

You can do this on the tail kit, no problem. It starts to be more difficult with other parts of the kit, though. You will get blocked until you install a small part, which of course means prep and prime.

You might be better off trying to come up with a system to prep and prime a smaller number of parts efficiently. It will pay dividends in the future.

avaviat said:

I do have a process question about building this beast. I have AKZO primer and am going to go through the whole MEK/Metal Prep/Alodine/AKZO cycle on the parts I prime.

Click to expand...

Jon,

Skip the MEK unless you are doing the tanks. On my -9 I scotch brighted the surfaces, Alumiprep'ed, Alodined, then sprayed them with self etching aluminum automotive primer from a spray can. I would buy the stuff by the case to save money. I'm almost finished with all the skins and have gone through 2 1/2 cases.

The only time I had a problem with the paint adhering to the aluminum was when the parts weren't completely dry. Typically I would prep the parts at the end of my work session, go to bed and spray them in the morning before getting in the shower and heading off to work. Then by the time I got home in the evening the shop wouldn't smell like paint.

The paint I used worked great and the advantage of the cans is you don't have to clean up a spray gun, which saves you a lot of time and aggravation. However, use whatever you are comfortable with, I was trying to point out that you don't really need to use the MEK to prep the aluminum, that's what the Aluminiprep is for.

Good luck and congratulations on starting your project.

I think priming everything at once is impractical. It probably works best if you do subassemblies. One tip I can give is to build a frame out of 1 by 2 lumber about the size of a front door and staple aluminum screen to it. In fact, an old screen door works perfectly. When it's time to prime stuff, you set this screen horizontally across a couple of trashcans or sawhorses or whatever (preferably outdoors) and put all your parts on it. This way the blast from the sprayer will go through the screen instead of sending your tiny pieces flying. There'll also be no pooling of primer to make parts stick to the surface. With AKZO you'll be able to flip them in about 15 minutes and shoot the other side. I know other folks hang everything from the rafters, but this takes forever and makes spraying very difficult.

Steve Zicree
RV4 Wiring

Since we all want to avoid the proverbial primer war I'll keep my opinion about priming out of the discussion but add one point.

Why alodine AND prime? One or the other is certainly sufficient for corrosion protection, and doubling them up doesn't "double" your corrosion protection. I've seen this practice more frequently as of late and am wondering who suggested to do a complete alodine and then prime on top of the alodine, and mainly.....why - this isn't one of those "some is good so more must be better" type of things...

Priming OR alodining is fine and I can see the benfit of either, but both?

Just my 2 cents!

Cheers,
Stein.

I think my bottle of Alodine says that it promotes adhesion of primer, and that my primer can label says to alodine first.

Steve Zicree

I also wish not to turn this into a primer war thread. So do yourself a favor and search here in the forums using the term "primer" and you'll have a couple hours of reading.

I personally prefer not to use the Alodine process because it can lead to corrosion in tight areas that can't be rinsed well.
You might be better of with a self etching primer where you don't need a pre-etch at all. Just my .02

A lot of good tips... looks like I'll be better off working out an easy/safe way to deal with the prep&prime process over the long haul.

A few specific points.. MEK...I'll try metal prep alone, but the MEK did a nice job of removing the printing and other markings on the metal.

The screen door sounds like a great idea! Parts going prematurely airborn were a real problem in my test priming. I tried hanging them but the little ones twisted so much it was nearly impossible to prime them well. Wound up putting them on cardboard and using an airbrush. Great for the little stuff, might be tedious for the larger parts..

Alodine alone... it seems like the alodine is too fragile to leave uncovered...maybe I'm wrong. My only experience painting aluminum was masts (spars in general) on sailboats, where anything less than acid+alodine+prime+paint would lead to creeping corosion.

Regarding the self etching primer... I just really love the green of milspec epoxy primer. One of my favorite colors. Anyway, I've got the two gallon kit of AKZO and the $50 bottle of thinner...I can't afford to go primer hunting any time soon. I put some in a HF airbrush and found I could store it (the whole airbush, with primer loaded) in the freezer for a few days and be able to use the primer whenever I wanted. I'm thinking of getting one of the primer sprayers that use a film can for the cup for spraying larger objects.

I would use MEK first only to remove the writing on the metal. The ink that is used has a nasty habit of showing thru primer and paint. Now wash everything with saop and a peice of scotchbrite. They make special soap for this but clear Tide or Ajax works. With everything now nice and clean do the Alumiprep and Alodine steps. Rinse well when finished.

Now that everything is alodined and dry, time to get ready to prime. I let parts dry over night but I make sure to prime within 24 hours. I try not to wash parts on a friday. Now here is a step when I use MEK again. I wipe down all the parts with MEK and a lint free rag. Not all of the alodine gets rinsed off. Some recrystalizes and sticks to the surface of the metal. It's hard to see but you can feel it.

Time to mix up that primer. Have fun.

Just a quick note about MEK. I'm sure you all know, but it's REALLY nasty stuff. While still being nasty, Acetone works just as well for removing all the printing on the metal, removes grease, etc.... and isn't quite as deadly as MEK.

I keep a lab squeeze bottle of Acetone aroune when working on metal, and rarely open the can of MEK unless it's a desparate situation. Most shops quit using MEK for routine things because it is cancer causing whether inhaled or absorbed through the skin, plus aceton is usually a lot cheaper and easier to find.

Just my 2 cents!

Cheers,
Stein.

avaviat said:

A few specific points.. MEK...I'll try metal prep alone, but the MEK did a nice job of removing the printing and other markings on the metal.

Click to expand...

Why use MEK? Lacquer thinner (or probably any other solvent) will take the blue printing, sharpie markings, and skin oils off at a lot less cost (about half the cost of MEK where I live) and less danger to you.

Good luck.

What's wrong with just using a thin coat of self-etching zinc primer? Why prime at all? The 40 year old Cessna I used to own didn't have any primer and it was still looking shiney and bright inside the wings and fuselage the last time I looked. Not one bit of corrosion anywhere. I suppose that it depends on where the airplane will be based and what conditions it would be exposed to.

Priming is always good, but some airplanes get away without it. Cessna primes ALL of their new aircraft, I think that teaches a good lesson. They learned.

I took the belt, suspenders, and duck tape...

approach to corrosion protection.

When I initially started on my -9 I had dreams of putting it on floats, thus all the extra care on corosion protection.

If I was going to start on a new project I really don't know if I do that all again or not. Truth is, with using spray cans it really isn't that much extra work and you have to prep the aluminum anyway so painting it isn't that much more.

Doug Rodrigues is correct, there are a lot of planes out there flying with no protection at all. It really depends on where you live in proximity to salt water.

The bottom line is similar to the tip-up/slider, tailwheel vs. nose wheel, & model selection debate. Build what you want in the way you want it. After all, you are the one who is paying the bills and will be flying it, not the rest of us.

WOW, guys...

Living right next to the ocean, I figure some sort of corrosion protection is in order. I'm very open to the possibility I chose the wrong type though.

How much lighter is rattle-can primer than a thin coat of AKZO? Come to think of it, how much weight does alodining add to the amount of structure aluminum in an RV-8A? (Not much on that latter question, I'm guessing.) I'm concerned that alodine alone is probably too prone to scratching given my ham handedness. The AKZO seems very scratch resistant, and of course being epoxy it is quite chemical resistant. The only downside I can see is if it weighs apreciably more than other primers.

I don't have much faith in the primers that are designed for a top coat until you top coat them. I've seen too many car parts rusting through the primer.

In the end, I think, "Build what you want in the way you want it..." says it very well...as long as what you (I) want isn't totally goofy.

Don't get too worried. You have a good set of reasons for priming your plane and have chosen a good primer that will do a good job. Even though I come across a bit "anti-primer" sometimes, I will submit there are cases where it's a good idea....like living in a humid salt water environment, flying on floats, etc..

You also make a good point about which primer you'll use. Many people forget that the primers for paint adhesion are just that...primers and NOT sealers. Before anyone starts spraying the inside of their plane with any old "primer", you need to make sure it's also a sealer. Putting color over the Aluminum doens't do you much good unless it also seals it.

You also right about another point. Alodine isn't nearly as durable physically as an EPOXY primer, but remember most of the pieces that you'll be priming / alodining won't be exposed to much physical punishment once it's built. It's pretty hard to scratch the inside of a wing skin or rudder skin once it's finished and if you're worried about scratching it during assembly, you'd probably scratch the epoxy as well.

Just my continued 2 cents!

Cheers,
Stein.

Not to beat a dead horse, but there are several suitable primers that do not seal. I think most ordinary zinc-chromate primers prevent corrosion through their chemical composition and not through preventing moisture transfer.

Steve Zicree
RV4