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Preparing Your Aircraft For Painting Part 3
Final Preparations and Painting Tips
By Tony Bingelis (originally published in EAA Sport Aviation, September 1985)
With the recent interest manifest in composite designs and construction, we tend to forget that there are still plenty of all-metal (aluminum) airplanes being built. Not only that, we overlook the fact that even those plastic jobs have a considerable number of aluminum components in them. That being the case, the unique requirements and methods for properly applying protective coatings to aluminum should be familiar to all builders.
I am aware that many builders are confused over the seemingly conflicting methods recommended for preparing aluminum for painting so let's see if we can't get a handle on the basics involved.
Aluminum when purchased will have a slick somewhat slippery film over its surfaces. This oily film, and fingerprint smudges, must be removed before you prime or paint it . . . otherwise, the primer and paint will not adhere properly.
The aluminum must be cleaned thoroughly. Wiping the metal with lacquer thinner is not effective as it only dilutes the oily substance and merely thins the film layer . . . adhesion remains poor. A second thought might be to wash the oily film off with water and a detergent. This is good, especially if you scrub the metal surfaces during the washing process with a pad of SCOTCH BRITE. Other methods for cleaning aluminum surfaces include the use of special solvents like the Metal Conditioners and/or Aluminum Cleaners that most paint companies offer. So, we have our first step:
A. Clean the aluminum surfaces in some acceptable manner.
Next, you have heard of surface treatments, I'm sure (Conversion Coating, Alodine Process, Phosphoric Acid Etch, Etching Primer, Wet Sanding with 400 Paper, etc.). They all do essentially the same thing . . . they dull the surface metal to improve adhesion of the primer and topcoats. The liquid or chemical treatments accomplish this by forming a dense non-porous oxide or phosphate film on the metal.
NOTE: Most paint companies offer two-part metal preparation kits consisting of (1) a container of a Metal Cleaner or Conditioner, and (2) another containing a Conversion Coating etchant.
The sanding treatment accomplishes much the same thing by providing a surface the primer can cling to. So now, we have our second step:
B. Sand and/or etch the aluminum surfaces.
The third and final step:
C. Prime the properly prepared metal surfaces, immediately!
There you have it . . . the ABCs of preparing aluminum surfaces for painting. NOTE: There are a number of very effective etching primers that could be used in lieu of a Conversion Coating or an Alodine treatment. However, in this regard, I would follow the recommendations of the manufacturer for the paint system selected. That's simple enough, isn't it?
Now, let's consider another matter.
Are You Going To Paint It?
There are considerations you might wish to weigh before you decide whether or not you will do the painting. For example:
You might be a builder aspiring to a "show-quality" custom finish where cost is no factor, or a builder who simply detests painting anything. On the other hand, you may be one who does not have the needed facilities or equipment to do any painting.
Without a doubt, other builders in a similar situation would want their airplanes painted by the best professional aircraft painter around . . . someone like Poplowski of Ennis, Texas, or Charles Day of San Angelo, Texas, to name but two in my territory. It would be very difficult for a builder to match the quality of a paint job completed in a dust and bug free paint shop especially equipped for painting aircraft.
There is another bonus in having someone else paint your airplane. It will automatically eliminate the need for purchasing, renting or borrowing a good compressor and spray gun equipment, respirator, masking materials and gallons of solvent, for cleaning everything later. Cumulatively, this equipment and materials stockpile is costly . . . especially when you consider that you probably may never again have use for the stuff.
On the other hand, it may be logistically or economically impractical for you to move the airplane to a distant paint shop to be painted. More likely, being a true-blue amateur builder at heart, you probably would want to paint it yourself. So much for that topic. You knew you were going to paint it yourself all along, right? O. K. Now, just where do you intend to have the magical transformation from ugly splotchy duckling to beautiful bird take place?
Overspray, the lack of adequate air circulation and poor lighting are problems that have to be coped with if you have to paint your airplane in the garage or workshop . . . especially if the ceiling is low. Furthermore, everything in the garage (or shop) will have to be covered and protected from the heavy paint mist.
Some builders have been fairly successful in putting up a plastic ceiling and plastic curtains inside the garage to form sort of a paint booth. Of course, they also had to use large floor fans to move the air through the booth. If you choose to try this arrangement be sure to anchor the plastic side panels securely to the floor lest the fans cause them to billow into your paint area. In such an arrangement, good ventilation is as important to your health as reducing the overspray mist is to a good paint job.
Painting outdoors, particularly under a tree, has its problems, too. Strange little things often drop out of the tree. And you have no control over the bugs or the wind and dust. Then, too, there is that blazing sun. But that is not all. You will have to take precautions to protect your own and neighbor's vehicles and other property from wind blown paint spray. You may also have to contend with curious visitors, kids on skateboards, dogs and health-kick fanatics who just have to stop and rest . . . and talk, and talk.
If you will be forced to paint under a tree in the driveway, you might consider it worthwhile to raise a plastic drop cloth or tarp "roof" above your paint activity. Incidentally, it may be wise to also spread a plastic or tarp floor . . . to keep the paint off the pavement and shrubs.
Of course, if no tree towers over the area where your painting is to be done out of doors, no overhead protection is necessary . . . unless, of course, you need it to shade your work from the sun.
Avoid, if you can, painting late in the day in direct sunlight. The sun will heat the surfaces hotter than the prevailing air temperature and cause the paint spray to dry on contact. The result is often a coarse surface finish or one that does not adhere well. The problem is more acute with quick-drying paints, dopes and lacquers.
Everything considered, the cool early morning hours are best suited for painting an airplane that must be painted out of doors. The wind is most likely to be calm and the bugs will still be sleeping after their usual night long orgies. The dust will also have settled in the tranquil air. The only flaw in this idyllic dream is that the humidity may be somewhat higher than it would be later in the day as the temperatures warm. Humidity, however, fluctuates from day to day and is characteristic of the type of air mass over your driveway. If you are not using dope or lacquer, the humidity factor is not as critical. In short, don't paint if the temperature is below 50 degrees F or if the humidity is over 75% unless the paint manufacturer indicates otherwise in his instructions.
Getting Down To Business
Put on some old comfortable clothes and shoes . . . things that you won't mind ruining with splattered paint. Don't forget to use the face respirator, even for quickie jobs, to protect you from the paint spray particles. If you don't believe the air around you will be full of spray mist wait until you have to blow your nose. Your handkerchief will provide stark evidence of what has been ingested into your precious lungs.
Another reminder . . . why not make an effort to wear safety glasses to protect your eyes from accidentally splattered paint?
Cleaning paint off your hands with solvents is not pleasant so why not wear cheap cotton work gloves? If that doesn't appeal to you, try applying a light coating of vaseline or some of that Hand Gel used by composite builders.
If you still have hair on your head, I would advise you to wear a cap or rub some vaseline into your hair, too, to keep the paint spray from sticking to it and turning your hairdo into something that would stop traffic at a Hard Rock Concert.
Since the base color (usually white) is sprayed over the entire airplane, very little masking will have to be done initially. Nevertheless, you must cover everything you don't want painted. Use regular masking paper (rolls of it may be found at many paint stores). If you like, you can use plastic sheets and plastic garbage or trash bags here and there. However, steer clear of newspapers unless you want the newsprint and comics to become part of your paint scheme. (see Figure 2)
Cover and protect your cockpit/cabin area taking special care to completely cover and seal the windshield and canopy Plexiglas.
You can cover your wheels and tires with the help of masking paper and tape, or a plastic trash bag slipped over each instead. This plastic bag gimmick works as well in covering the propeller, tail surfaces, antennas and tail gear.
Finally, don't overlook masking the smaller accessories like the pitot tube, drains, vents, air inlets and lights if you don't want them painted.
Avoid using cheap masking tape directly against the aircraft's surfaces. Some brands of cheaper tape have an adhesive that sometimes remains as a residue stuck to the painted surface after the tape is removed. Others have an adhesive that sticks so hard after a few hours that it could pull paint when you try to remove it.
Another problem with ordinary masking tape is that caused by its crinkled edges. It seems that no matter how hard you try to press down the edges, the paint will still bleed under it and will yield a fuzzy color line . . . most embarrassing.
I like 3M's SCOTCH Brand 218 Fine Line Tape (1/4" and 3/4" widths) and their SCOTCH 33+ Vinyl Plastic Electrical Tape. That black electrical tape with its smooth edges does a fine masking job. Because it stretches so easily, it does require a good eye and some artistic skill in applying it in a straight line. For masking curved lines, it's great.
To save money, you can use all the cheaper masking tape you want anywhere it will not be in direct contact with the aircraft's painted surfaces.
Airplanes are being repainted fully assembled, of course. A first time or original paint job is better accomplished with the major components disassembled, I believe. (see Figure 1)
Maybe your spray gun doesn't drip a drop or two of paint on a beautifully sprayed surface when you least expect it but mine does. I cure this maddening tendency by wrapping a loosely rolled paper towel around the gun just under the spray nozzle and stick it in place with a piece of masking tape. Any drip is caught by the paper towel bib.
Try to buy all of the base color paint you will need at one time. Then you will be assured that all parts of your airplane have the same hue. Even those computer mixed paints have a way of getting off in the color tone from one batch to another. Just to be sure, you could mix all the individual cans together into a single large container. Then you will be sure you have a uniform color throughout.
Use the correct solvents for the temperatures expected. Re-read the printed instructions and follow the thinning directions exactly.
Don't rush! Allow yourself plenty of time and observe the minimum recommended drying time between coats.
After refilling it with a fresh batch of paint, ALWAYS clear the gun with a couple of short test blasts before aiming it at the component to be sprayed. A short blast against the masking paper or even into the air will assure you that the spray pattern is uniform and that the gun is properly adjusted.
Being extra cautious and spraying on a light coat is just about as bad as spraying on one that is too heavy. The light coat will probably take on a misty orange peel appearance because there is insufficient paint to flow out into a smooth gloss. However, an excessively heavy coat is an invitation to sags and runs. Somewhere in between those two extremes is what you are after. You will find that happy medium easier to find the more parts you spray. For this reason it would be a good idea to get as much practice as possible by spraying all the small parts and components first.
Spray the surfaces in a cross pattern beginning with the vertical strokes first and followed immediately with the horizontal movements of the gun over the same wetted area. This pattern of spraying will help you obtain a uniform coat without the development of light and dark areas which are never discovered until you have put away the gun.
Handling Bugs And Boo-Boos
Bugs getting into your wet paint? If you are painting outside you can almost bet on it. What to do? Do nothing initially unless they are of the large winged variety and are doing a lot of heavy wing flapping. Remove that type immediately with tweezers. Dip the tweezers in paint so that the ends are sticky and you can get a better grip on the rascals.
The other random small bugs are best ignored until you have finished spraying that particular panel or component. You might then try to blow the bugs off with an air nozzle fitted to your air hose. Don't get the air nozzle too close to the painted surface if it is still wet or you may cause ripples. If you have any doubt at all, wait until the paint dries and the bugs can be brushed off leaving little or no trace.
Just about the same advice is applicable to paint drops, sags and runs. Allow them to dry. They can then be dressed out with 400 and 600 pound wet paper and rubbing compound. The process works better with doped and lacquered surfaces than it may with some other paints. Again, follow the manufacturer's suggestions.
One final reminder. Always, just before you spray any part of any surface, wipe off the dust particles with a Tack Cloth. Make a habit of doing this just before you pick up the spray gun. Carry that Tack Cloth in your pocket where it will be easy to reach any time you need it. Incidentally, never use ordinary rags that might leave lint on the surfaces, and never use a shop towel. It might be contaminated with silicone traces if someone else had used that same cloth for waxing his car.
A Parting Thought
You can't learn how to manipulate a spray gun like a pro simply by reading about it. You can, however, learn how to avoid a hundred and one pitfalls that others before you have already discovered - simply by following instructions. It's easier than you think. Ask any builder who has done it.