Priming is a dull but necessary work if you want to protect your airframe for the test of time called corrosion.
The 2024-T3 aluminum of Vans is already covered with an Alclad layer which by itself should already provide protection. However, many of us builders choose to increase the protection layer with an additional coat of primer.
Many debates have been held on priming and priming procedures. It's such a big topic with so much discussion that you will often hear the term 'primer wars' in the forums.
I have personally choosen for the zinc-chromate protection process. It is a high poisonous product that can lead to cancer if not protected well by respiratory filtering. So be aware !!! This is not stuff to joke about and certainly not to think you'll get away with it just once...
YOU WON'T ! ALWAYS.... ALWAYS make sure you are protected.
My protection consists of:
- a full suit coverage of light plastic over my normal clothes with head coverage.
- rubber boots
- light surgical plastic gloves and on top of those a set of heavy rubber gloves.
- A 3M full face mask with double carbon filtering. If your's is not full face, make sure you wear closed plastic glasses to prevent the product to enter your body via the eye openings
- wear earpluggs again to prevent product to enter your body.
That being said, let's talk about the procedure of applying zinc-chromate to bare aluminum.
Step 1, clean the raw material with degreaser. This will clean the material from any type of grease that will prevent the primer from sticking.
I clean with Silikon Entfermer® from Spies Hecker™ (Silikon Entfermer 7010) to remove grease from fingers etc. This must all be re-done just prior to priming.
Step 2, I thouroughly clean with aceton® and clean paper towels to remove the sharpie pen ink. It is not a good idea to leave the pen markings underneath the corrosion protection.
Then, gently and lightly scuff the material with maroon/red scotchbrite pads. This doesn't need much, just lightly scuff it up so micro scratches appear on the surface. The surface will no longer be shining but will become rather dull.
A lot of people are concerned about taking away the alclad layer when scuffing the material. I found the following remark in a forum very sensefull and helpfull:
"I was an airframer (rivet banger) in the Navy and spent 9 years after the Navy working as a machinist in a tool and die shop. Trust me it would take some major elbow grease to wear through alclad with a maroon scotchbrite
pad. Just some food for thought I belive a beer can is approx. .003 thick (The last one I checked several years ago was) and lets say that the alclad is .002 thick. Think about how much effort it would take to rub through two thirds of a beer can with a scotchbrite pad. "
Step 3, after scuffing, and just before priming, repeat the step 1 cleaining but this time with a real clean piece of soft cloth that is full wet with the sillikon entferner. Apply the product in one direction only. Then take a dry clean soft cloth and go over the material again rubbing in the same direction. Do not let the material dry by itself. You have to dry off the product after a minute or so.
After step 3,make sure you don't touch the material anymore with bare fingers.
Step 4, priming time...
Priming is achieved with a HVLP spray paint gun.
HVLP stands for High Volume Low Pressure.
The pressure setting for the gun is written in your gun manual. Take care not only to have a setting on the compressor, but also buy a little gauge that sits just at the entry of your gun. At this location, you need typically between 18 and 25PSI while spraying. So adjust your air linet while spraying air.
Set your compressor about 20 to 25 PSI higher then the entry setting at the gun. This will ensure enough pressure at the gun but also won't kill your compressor in continuous recharging.
A spray paint gun has a number of adjustable parameters: the air inlet pressure, the volume control, the spray fan control and the spray direction.
There are many interesting links on you tube that show you how to use a HVLP gun.