Primer wars – The never ending battle! (by Andy Karmy, RV9 & MiniMax builder)

So you spent months, even years researching the perfect plane for your “mission”. You looked at fast glass (yuck epoxy fumes), you looked at “classic fabric” (yuck MEK fumes), you finally picked “traditional aluminum” (Look it’s non toxic, low up keep, and easy to work with…).

Then the other shoe dropped and you found out that while yes you could just build it bare, that’s not really recommended for the northwest climate conditions. So you were introduced to the great Primer debate!

What primer to use, how to apply it, terms like mixing, reducing, shooting (who get’s shot here?), film thickness, solvent tolerance, and a host of other technical details. Welcome to homebuilding education 101 is the name of the game.

Most builders are a very traditional bunch and the products in use to prime aluminum have been around for a long time. The main problem with them is they all are based upon toxic solvents. This means they try and kill you, while you are trying to keep the elements from killing your airplane. What’s a poor homebuilder to do?

Enter Aircraft Finishing Systems of Ennis Montana. They recognized that due to government regulation, personal health and other issues, there was an up and coming market for environmentally friendly, user friendly paint products. They have developed a complete line of water bourn paint systems for wood, metal, fabric, & fiberglass. Originally the primary consumer of these new products was the large commercial jet painters & manufacturers as they needed a product that would work great in harsh environment that jet’s live in, but free them from the large hazmat fees that they had to pay to dispose of the amount of solvents it takes to paint a large jet. The same chemist that developed the certified paint system “JetGlow” developed the top coats for AFS.

Ok, all that’s neat, but all I need to do is prime the insides of my RV. So on we go. There are 2 primer products that AFS offers. The first is a 2 part epoxy primer which sticks very well and works great as a primer, however for this purpose we don’t specifically want a “primer”. It turns out that the reason you want a primer is to give a good sticky base to a finish coat and hold it onto the base material. To do that well a primer has to be porous so the paint can grip into it nicely and not flake off. In our case we want something to protect the aluminum from the elements so they have another product. It’s a 1 part primer sealer which adds just a bit of a gloss top coat to it, so you get both the base primer and a sealed surface the resists corrosion for the life of the part.

This 1 part primer / sealer is great to use. It goes on easy, cleans up with water, dries quickly, and provides the corrosion resistance that we need. So, what’s the steps to put this stuff on you ask? Here you go:

So, you caught me, what’s this aluminum etch you ask? Well the owner of AFS, Paul, has painted many airplanes over the years and he has had the opportunity to strip planes for repair and repaint that were painted with most of the “self etching” primers on the market. What he has found is that in general you never get a complete even etch of the base metal with a self etching primer. There are areas that don’t etch for some reason or another and the adhesion of the primer is weakened. By doing a separate etch step you can ensure a good etch that will hold the primer on there for good.

What gun do I use? The basic $40 top load HVLP conversion gun from Harbor Freight. It’s bone simple, works great and cheap. The great part is that you can use the cheaper models with the water based products since they don’t tend to gunk up the insides of the equipment and are easy to clean out.

Shop temps? I paint everything outside. If the temp is 60deg or higher the paint flashes off quickly and dries between your 2 coats. Under these conditions you get a nice smooth application of the primer and everything works great. I have sprayed in temps as low as 40deg and it works, however the paint won’t flash dry, so when I take it inside to the heat it does run a bit while the water evaporates. I put up with it for the few times I need to paint during the winter since it’s on the inside anyways. It dries to touch in about 5 min. However it takes about 24 hours to harden. If you start handling it before then the primer will scratch easily. After a few days it’s very hard and won’t come off.

Why did I choose this product you ask? I am building in an attached garage, and my family can’t put up with the constant smell of solvents coming from the airplane factory. I investigated the AFS products while building my wood & fabric MiniMax as I needed an alternative to the MEK based Stits process. I found AFS and have been spreading the word ever since.

One last question always asked… Does MEK wipe it off after curing? With the 1 part primer / sealer yes MEK will remove it. The 2 part Epoxy won’t come off with MEK or other solvents once cured. My basic answer is, when was the last time you flew through a MEK rain shower? This stuff is good for hundreds of hours in a salt spray bath; I think it will keep my hanger queen RV looking nice for years to come.

Cost is $76 per gallon or $20 per quart. You can buy it from a number of dealers. I got mine from Starduster (the biplane guys) in California. (to buy it from starduster) (for more info direct from the manufacturer)

Aircraft Finishing Systems

PO Box 16418
Missoula, MT 59804

Ph: 406-251-1373 or 1374
Fax: 406-251-1375