Priming is one of those RV arguments you just don't want to get into. Priming is the coating of the internals of your airplane so mother nature doesn't impose its rath on your precious plane and leave it in a pile of dust one day as you open up your hangar. There is not a one or another approach to priming (like other RV decisions such as tip-up or slider canopy) - there are probably a dozen or more methods for priming - from not priming anything to using Alumiprep/Alodine/2 Part Epoxy Primer to everything inside your airframe.

I started out priming my empennage using the "Checkoway Method" - Alumiprep, Alodine and AKZO 2 part epoxy primer. I didn't really know what I was getting myself into, and not knowing anything about building, it seemed to be the bulletproof method for priming. A bit of advice - I ordered all of the chemicals from aircraft spruce. The shipping was incredible expensive - $77 on a $155 order! All of these chemicals are hazardous materials (HAZMAT) and cost a lot extra to ship. I have found local sources for everything (except AKZO) at local auto paint stores (Sherwin Williams) and marine stores (West Marine). Also, buy all the chemicals you can locally - not only for the shipping savings, but my AKZO primer was so badly banged up in shipping that the top doesn't close tight at all.

Anyways, the first thing I did before priming was to clean all of my parts off with a solvent. Some people use MEK or acetone, but I find those two chemicals way to hazzardous for me. I had good luck with laquer thinner, and another local builder highly recommended PPG's DX330 degreaser. Personally, I don't go too hard at it to try to get everything perfect because there are many other steps in this priming process. I mainly cover everything lightly to get the oil off of it from hands/air tools and any markings off - Oh, by the way, you should have your parts marked with an electric engraver so you know whats what. This step will surely take off any sharpie marks you have on your parts. From now on out, only handle your parts with gloves - some people use cotton gloves, some use latex gloves. Just don't use your hands or the tongs that you just BBQ's your steak on the grill with.

Next I used Alumiprep as a mild acid used to clean, dull and etch the aluminium. I mixed it in a spray bottle in the indicated ratio with water. I first spray down the part, then scrub it with a maroon scotchbrite pad, then rinse. You know that you did enough when the water doesn't sheet off of the aluminum. Also, don't let the alumiprep dry on the part. Keep is wet with alumiprep and then rinse it off.

Next is the alodining process. Alodining is a chemical conversion process of oxidizing the surface of aluminum to all paint to bond to it better, as well as to serve as a corrosion barrier. There are two ways to apply alodine - the first is to brush it onto a part, and the other is to dip the part in a alodine/water mix. The dipping gives a far superior finish, but it also takes a lot of alodine to dip a big spar. I didn't dig how brushing it on left the surface. Anyways, Alodine each part for 5-10 minutes and then rinse. Just like the Alumiprep, don't let the alodine dry! This step is my least favorite part of the process.

One trick I do between the alodine and priming stages is to go through the parts after they have dried and find my markings for the parts and remark them with a sharpie. I have a really hard time finding the markings once the primer is on. The shapie bleeds through the AKZO nicely.

Finally, I mixed the AKZO primer. You have some time to mix it since you need to wait for all of the parts to dry. My method for preparing the primer is to first mix the primer throughoutly. It seperates pretty good in storage. I use a drill attached stiring device I picked up at Home Depot. Once that is done, I use a stainless steel ladle (Target) to dip the catalyst (the more translucent of the two chemicals) into a Pyrex GLASS measuring cup (Target). Next I clean the ladle off with acetone or laquer thinner and then dip out the primer into the pyrex glass. I hand spin the mixing doohicky and let it sit for 30 minutes to setup, mixing it about every 10 minutes. Pour that stuff into your spray gun and go at it! I use a very very thin coat. It is hard as nails in 15 minutes and ready to go.

One word of advice on spray guns. First off, I don't know jack about them because this is my first time using one. Secondly, mine is a gravity feed HVLP (High Volume Low Pressure) from Harbor Freight ($40 on sale). I like it because it is easy to clean and because it is gravity fed, I don't need to worry about mixing so much primer just to make sure a tube can reach it to pick it up. My $40 gun works GREAT. Just practice before you use it. My practice was my horizontal stabilizer and I wasn't happy at all with how it turned out (don't get me wrong, it is completely functional!).

In my time between the empennage and the wings, I did a lot of thinking about how I would prime differently. The easiest route would be to use spray can primer (Sherwin Williams GBP-988 and Marhyde are popular amongst builders). I bought a can of the GBP988 and played around with it. It gave an OK finish, but it wasn't nearly as bulletproof as the AKZO. I did some more digging and found that spray can primer is not a sealer, and is meant to be topcoated. Now, Van's on their quickbuild use a wash primer that they stand behind, so there is nothing wrong with using just a primer that isn't a sealer. But for me, I didn't want to chance it. Maryland gets super humid for a few months in the summer and I want some decent protection just in case. It's only time after all. One thing that I am experimenting with is not using alodine. It is my least favorite step, and I think I will get good results without it. Not to mention it is the most hazardous stuff I deal with in close proximity.

Update 9/4/2006

After moving to my new house I don't have a nice place to dispose of that nasty alodine stuff. I don't want it to wash into the drainage system, nor do I want it to run off the driveway into the yard where it could be absorbed by bare feet. While doing some R&D on the subject at work, I stumbled across a thread on the matronics website that has a letter from AKZO that states:

The simplest way to prep the aluminum is to wet abrade with scotch
brite and water, followed by solvent cleaning with acetone, or MEK, or
toluene.  The alternative is alumiprep 33 acid plus alodine 1201
conversion coating.  This is not preferred because of the hazardous
chromates in alodine.  

In either case, before priming, it is essential to remove the thin oxide
layer that forms on aluminum.  Scotch brite or acid etch will accomplish
this.

Good luck.
John Griffin
Sales Manager
Akzo Nobel Aerospace Coatings
john.griffin@wau.akzonobel.com
PH:       502-721-8109
Fax:      502-721-8043
Mobile:  847-612-5157
That's all I need to hear to skip the alodine process. My new process will be to wipe the parts down with acetone or laquer thinner to remove the oils, then alumiprep, and finally prime. That seems to be the least hazzardous method to using AKZO.

Update 03/22/2007

I have gotton all the way through the wings and have my priming method down now. It is amazing how it evolves. Before priming was my least favorite thing to do - but now it is a walk in the part (including cleanup). My FINAL method is the following:

  • Debur everything and then scratch everything up with a scotchbrite pad to make the primer stick to the alclad parts
  • Don't dimple until after priming. I found that it is easier to get the primer evenly spread over non-dimpled skin. The dimple can leave a shadow of primerless aluminum.
  • Spray alumiprep on the parts (diluted 1:3) with a spray bottle. Let sit for 5 minute and spray off with water. I use the highest pressure water possible to take as much dust as possible from the first step.
  • Let the parts dry. Sometimes I accelerate this with wiping them down with rags or hitting them with compressed air or putting a halogen light over them.
  • Clean the oils and dust off the parts. I use acetone to accomplish this. Some people will disagree with my order here, because oils from your hands could technically get embedded into the aluminum from step 1. I understand that, but to do it that way you would have to expose yourself to these chemicals twice - once to remove the oils before step 1, and then again to remove all of the residual dust in this step. In addition to cleaning the parts, acetone also absorbs water. So if there are any wet spots from washing the alumiprep pff, this will get it.
  • Mix the AKZO and let sit for 30 minutes. I usually mix in the catalyst first, and then the primer, wiping down the ladel in between.
  • Finally, prime the parts and then cleanup. Thats it! It sounds like a lot of work, but for small batches it can be done in a few hours.
  • Found this info on the VAF Forums - recommended temperature and humidity for spraying AKZO. In the winter time it is impossible to get the garage up to 59F, especially with the garage door open to the cold outside. I have shot it successfully in the 40's.

    59F - 95F (15C - 35C)
    Relative humidity at 35% - 75%
    


    http://RVplane.com

    Last Modified: July 27, 2014