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Painting Your Homebuilt Part 2
Lessons Learned and Relearned
By Tony Bingelis (originally published in Sportplane Builder, January 1995)
Here's why surface preparation is so important . . .
Paint will only color the surface to which it is applied. It will not hide:
1. Rivet heads - especially the pop rivet variety
2. The slightest scratch or scuff mark
3. The smallest dent
4. The tiniest of pin holes in a fiberglass component
5. A bump, or any kind of surface roughness
I must admit, however, with some chagrin, that I apparently have trouble convincing myself this is truly so. It is only when I carefully examine a freshly painted surface and find small areas where my preparation work wasn't all it should have been that the lesson sinks in. My most persistent fault is in not taking the time to sand away the faint sandpaper marks left by coarser grades of sandpaper. Don't be guilty of making the same mistake.
Discipline yourself to sand away all signs of surface roughness and scratches with progressively finer sandpaper. Finish your surface preparation using #350 grit wet/dry sandpaper . . . #400 grit is even better. Neither grade will leave visible sanding marks. Incidentally, using the fine grit sandpaper with water allows it to cut better and keeps the sandpaper from clogging.
I say, again, if you want a good paint job, you must remove all the dents, scratches, pin holes, and other imperfections before you pick up the spray gun and shoot the first coat.
Unfortunately, pre-paint preparations, up through the primer coat, are quite demanding and entail a lot of hard work. You will find, for example, it takes up to 50 times longer to prepare the surfaces than it does to spray on a color coat.
Although each type of aircraft construction may require preparation methods that differ somewhat, they all have this in common. Each type of construction - be it metal, composite, wood or tube and fabric - requires many more hours to be spent in surface preparation than in painting. Many builders do not realize that the prefabricated polyester fiberglassed components they receive will continue to shrink for months after manufacture. Consequently, you can generally detect the weave pattern of the glass cloth through the gel coat. This pattern will also show through the finish color coat, especially on your cowling, although it won't be as obvious to the casual observer. If this bothers you, minimize or eliminate the textured appearance by giving your fiberglass parts, particularly the wing tips and cowling, a couple of fill coats of a good sandable primer. Sand between each coat using a medium hard rubber sanding block to back up your #350 or #400 wet/dry sandpaper.
Incidentally, sanding with straight line strokes is not the best way to do it. You will obtain much faster and more uniform results if you sand in a circular motion. After you have completed all sanding preparations, blow off the sanding dust with an air hose. Poke the nozzle into all the corners. If you don't, any entrapped dust will be raised by the spray gun air blast, and some of it will settle in your finish.
Finally, examine every square inch of the newly prepared surfaces. Pay close attention to all the edges. These should be sanded or filed smooth and slightly chamfered. It is along these edges where there may be some overlooked felt pen markings. All marks you find must be completely removed using plenty of thinner. An overlooked ink mark notation, or ink line, will surely bleed through your nice finish and will cause considerable regret later.
What To Do About Pesky Pin Holes
Only fiberglass parts are capable of producing such an obnoxious blight in a finished surface. Pin holes show up most in fiberglass layups, and especially in factory made components when some of the gel coat has to be sanded to the bare fiberglass surface. Spraying primer, or paint, over pin holes is futile because the paint merely straddles the tiny holes and the pin holes become even more visible in the final finish. The cure for eliminating pin holes is to fill them by using 3M Spot Putty, or a similar automotive filler (personally, I like "Marine Tex"). You can also brush a sandable primer over the holes and rub the stuff in with your fingers until they disappear (I mean the holes). After the pin hole filler has dried, sand the area smooth. You may find that a second treatment is often necessary after you inspect the sanded results.
Unfortunately, pin holes are not easily spotted until the surface has been primed. Even so, you might miss quite a few pin holes that will, to your disgust, show up in the finish coat. What can you do when more pin holes show up in the finish coat? That's right, you'll have to live with them unless you have the resolve to re-treat and refinish the part.
The Art of Masking
If you want a quality paint job you must be willing to use quality products. I believe the tapes best suited for masking color line separations is 3M's "Fine Line Tape" or a good grade of Mylar filament tape. They produce masked lines so sharp that trim colors rarely bleed under their edges. The tough fine line tape with its polypropylene film backing cannot be torn by hand. It has to be cut with a razor or scissors. The 1/2" width is the most practical to use.
Another tape that I find to be excellent for trim striping, and for use against Plexiglas(tm) windshields and canopies is the 3/4" wide black electrical tape. It is quite inexpensive and, being very thin, can be easily stretched around sharp curves. It, too, leaves nice clean trim lines after the tape is removed.
On the other hand, the ordinary 3/4" wide (crepe) masking tape most of us buy because it is inexpensive is not as effective to use for striping because paint will sometimes bleed under its edges and leave a fuzzy looking trim line after it has been removed. As a rule, I never use the ordinary crepe masking tape against a finished surface. Instead, I use that kind of tape primarily for attaching the masking paper to and along the fine line tape color separation striping. Both the fine line tape and the electrical tapes are easy to remove. I can't say as much for the crepe masking tape which is often difficult to peel off if left on too long.
If you have to touch up or refinish your instrument panel, here is the easiest way to mask it when the instruments are already installed:
1. Cover the glass face of each instrument completely with strips of ordinary masking tape. You can do the job quicker if you use masking tape at least one inch wide.
2. Run your fingernail around the perimeter of the glass face to seat the edge of the masking tape tightly.
3. Next, using a single edge razor blade, run its cutting edge around the instrument glass.
4. Peel away the excess masking tape leaving the instrument face completely masked and the panel is ready for painting.
Obviously, it would be much easier to paint the instrument panel before installing the instruments as no masking would be necessary. However, during the installation of the instruments and other cockpit work, the day may come when you need to refinish the panel without all the work involved in removing the instruments.
No matter how careful I try to be in masking the various components, I sometimes find a spot or two where the paint has bled past the masking paper and tape. The blemish is usually a small spot or a triangle of fresh paint that somehow leaked onto the primary finish I intended to protect. Unfortunately, the discovery is made only after the masking paper and tape has been removed. The best way to prevent that sort of thing is to carefully examine every single inch of the masked edges to assure yourself that the masking paper covers everything and that the tape is down tight. Assure yourself, too, that all overlapping edges are taped tightly. Cut the tape with a razor if necessary to make the tape behave.
Your Plexiglas(tm) canopy can't stand much abuse. Keep it and the windshield completely masked, both inside and out, while any kind of painting job, no matter how small, is being done anywhere near it. This will protect the Plexiglas(tm) from accidental overspray . . . and save you from a lot of cleaning and polishing later. As you may have noticed, I use a variety of "masking" tapes.
1. The most important is the 1/2" 3M Fine Line Tape. This is the tape professional painters use to outline the color separations or trim design. It is affixed directly onto the surface you want to mask. Cheap masking tape is O.K. to use but it must never be used in direct contact with a finished surface. Instead, use it to attach masking paper to the fine line tape already in place.
2. A third tape I use often is ordinary black electrical tape. It is theonly kind of tape I ever use to mask off windshields and canopies.
Because its edges are extremely thin and smooth, laying out clean cut curved lines are possible when you use it. It is easy to apply and just as easy to remove without leaving an objectionable residue. Unlike ordinary masking tape it may be left on for a fairly long time (a week or two) without becoming difficult to remove.
The best masking job results when you use regular heavy duty masking paper, not old newspapers or plastic sheets. Be sure the masking paper you use will not allow the paint to bleed through it. If it does, you will have one big problem, amigo. I don't recommend using large plastic sheets as asubstitute for masking paper. You may overlook covering all the areas you want protected because the plastic is transparent and you may not notice places left unprotected by the plastic. A roll of 14" wide masking paper is not too costly when you consider it may save you from a botched up paint job. Using large sheets of plastic to supplement the areas properly covered with masking paper is O.K. but be absolutely sure the loose end of the large plastic sheets are taped down to prevent breezes from blowing an unsecured corner up into your freshly painted surface.
It happened to me once. Consider yourself warned, so don't blame me if it should happen to you, too. Before you paint, go over every inch of the masked line, running the back of your finger nail alon the edge to be sure it is down tight against the surface to be painted. Masking paper can be removed in an hour or so after painting. Do it carefully and be sure you don't allow some of the masking paper, or the loosened tape, to accidentally contact the fresh paint.
I like to remove the masking tape and paper before the paint dries hard overnight. That kind of delay in removing the masking tape may result in a fuzzy brittle edge between the two colors.
Painting Traps Can Be Avoided
Failure to read and follow the paint manufacturer's instructions often causes the most grief for th new builder. Follow the manufacturer's mixing recommendations by carefully measuring out the correct amounts of color, reducer, and hardener as instructed. The most common finishing flaw, other than runs, is the orange peel appearance of an otherwise nice smooth shiny finish. It is usually an indication that the paint should have had more reducer (thinner) added to allow it to flow out better.
The risk, however, is that thinning paint too much (especially in cooler weather) will increase the risk of producing runs. Of course, when temperatures are high, more thinning should be anticipated. Your last act before pulling the trigger on the spray gun is normally a quick wipe of the surface to be painted with a tack rag. A tack rag is a very inexpensive, sticky-feeling type of rag especially treated for a very special purpose . . . to pick up dust. It is the one sure way to wipe off those last minute dust particles that may have gathered on your surfaces.
Painting vertical surfaces requires the greatest care as making one pass too many with the spray gun will result in runs or sags . . . especially in corners and at lapped joints, or where you inadvertently let the spray gun get too close to the surface. And yet, if you don't give the surface at least three good passes you may not get the flow-out and gloss you want.
At any rate, as soon as you have completed spraying a component, whenever possible try to turn the part you have just painted to a horizontal attitude to lessen the risk of paint runs. I hate to say it again but paint runs are prone to occur when the paint is thinned or reduced too much. And yet, if it isn't thinned enough you may get that "orange peel" appearance in the finish.
Don't be in too great a hurry to wipe away a small paint sag or run. It might level itself and become inoffensive after the paint cures . . . especially if the surface can be turned level immediately after it has been painted.
Inspect the Finish For Flaws
After you have finished painting, inspect your work closely. Hopefully, you won't find any, but here are some flaws to look for:
1. Small areas that didn't get painted, or didn't get enough paint.
2. Places where the paint leaked past the masking paper or masking tape .. . usually where there is a gap between parts or where there is a lap joint.
3. A place where you may have, inadvertently, brushed against the freshly painted surface with the spray gun, the hose, or your sleeve.
4. Spots or small areas where the paint just seemed to separate and refused to cover. Most likely that particular area was contaminated by oily fingerprints, or wasn't properly cleaned and "degreased."
5. Any localized runs, curtains and sags that you didn't notice before. These occur most frequently in corners, joint laps and on edges.
6. Felt pen or "Sharpie" ink marks that you overlooked removing completely.
You didn't find any? Congratulations!
Marine Tex is an excellent two part spot filler that will not shrink. Most marine and boat sales outlets carry it.
If I had to paint a homebuilt before I could get to build it, I probably would never start on the project in the first place . . . figure that one out, amigo!
To me, painting an airplane is on a par with building cowlings and doing other fiberglass work . . . both efforts are messy and both stink. I would rather whittle wood and drive rivets. However, painting comes with the sport so I try to do the best I can for every project I undertake. S re, I could have somebody else paint my aircraft - and I would if I could, but I can think of several thousand reason for doing it myself (read that as "dollars").
Anyhow, it is not that I can't do a pretty good job of painting. I can, but since I don't use my spray gun for two or three years at a time, I have much to relearn. Consequently, my results, at least initially, are not always predictable and consistent. As a confidence booster, I try to convince myself that there is no such thing as a perfect paint job . . . it helps.
I realize that anyone who is picky enough can always find something to criticize in the finest paint job: a masking flaw, a small run in some corner, a pin hole or two in fiberglass parts, a slight "orange peel" appearance where least expected, or maybe a paint starved edge. Anyhow, my latest project, a little single seat RV-3, has finally been painted, and with fairly good results, I might add. This time I took plenty of time to mull over the problems I experienced during previous painting efforts.
For example, I well remember how I had to cope with the problems of spraying the airplane in the driveway, the messiness of it all, the bugs and the tiny dust particles, the masking mistakes, the consequences of over-spray, paint runs (always where they showed the most), and, yes, even
the mild elation I experienced when I managed to turn out a few perfectly sprayed components and parts.
If you intend to paint your own airplane and have never had the occasion to spray paint an airplane, a car, a boat or an automobile at some time in your life, why not go for it? Not only will you save money, you gain a real-life experience in the process. I'm sure you realize there is much more to painting an aircraft than simply selecting the paint, spray gun, reducers, masking tape and a place to perform the ritual.
You're right. There is quite a bit in the way of painting preparations and techniques the average builder never hears about. Maybe the paint manufacturers take it for granted that only professional painters paint airplanes and they already know the tricks of the trade. Unfortunately, that is not usually the case as there are many of us who restore autos, or build airplanes and boats, and determinedly elect to paint our own creations. Nevertheless, although we are amateurs many of
us are turning out some beautiful work.
So, regardless of how little you think you know about spray painting and pre-painting preparations, why not go for it? This article is based on what I have learned and what I have had to cope with every time I started to paint a newly completed airplane. It may give you a better grasp of what to expect when you plan your own painting extravaganza. After all, it is much easier to avoid most painting pit
falls when you know where and why they develop. NOTE: I generally use DuPont's Centari Acrylic Enamel on my homebuilts because it is less expensive and its fumes are less toxic than those emitted by the exotic Polyurethane "wet look" finishes. My comments are, therefore, specifically oriented to the use of acrylic enamels. Nevertheless, most of the precautions and preparations described are, I am sure, equally valid for most any kind of painting project you choose to undertake.
Let's face it. Painting an airplane at home is as bad for the environment as it is for your lungs! The culprits, of course, are the paint fumes and the overspray spewed out by the spray gun. To reduce the amount of excess paint spray that does not land directly onto the component you are painting, consider using one of those remarkable high volume low pressure (HVLP) spray units. These turbine units produce, at a very low pressure, a very high volume of heated air that operates the spray gun. This heated air coupled with the gun emits a cone-shaped spray pattern that reduces the relative humidity in the surrounding air, and the overspray as well . . . provided the wind is not blowing.
Almost a third less paint will be needed because of the greatly reduced amount of overspray. The environment, naturally, will benefit from the use of such a paint spray system as much as you will.
Even so, your assault on the environment and on your lungs is not over because after you finish using the spray gun, any kind of spray gun, you must clean it. Of course, you never set the gun aside and let paint harden in it. If you do, you'll regret it the next time you have to use that gun.
Now . . . how do you clean a spray gun? That's right . . . with copious amounts of lacquer thinner, or some other highly volatile solvent. Meanwhile, as you brush and/or spray the fluids through the gun, plenty of fumes are being turned loose in the air around you. These are the same volatile solvents you will use to clean up whatever paint spilled mess you make. Actually, you will have used several gallons of solvents by the time you complete painting the airplane. All of the leftover paints and dirty solvents remaining in the gun, and in various coffee cans on the bench, have to be disposed of. So, what do you do with all that stuff? Pour it down the drain? On the ground? If you do, that paint residue and dirty fluids will discolor and contaminate the soil where it is dumped.
A more sensible solution would be to conscientiously collect all of the waste paint and solvents in a large container - and keep it tightly capped. Then, after you have completed your painting project, haul it away to an approved disposal site . . . it is the right thing to do. If you live "out in the country," resist the temptation to pour out the leftover paint and solvents on the ground in some private dump site. Think twice - that stuff will permeate the soil and may even get into the underground water supply.
Think About Your Hands
I say again, painting is a messy operation. No matter how careful you think you will be, that hard-to-remove paint will get on your hands and under your fingernails. That's bad enough but the solvents will also penetrate and dry out your skin. Without any protection, your hands quickly become so paint stained that no amount of scrubbing will get the paint off for several days . . . a social disgrace, indeed.
Although you may consider using vinyl or rubber gloves awkward and inconvenient, they will help keep your hands clean. Unfortunately, these protective gloves don't last very long when you handle paint reducers, lacquer thinners and similar volatile solvents because they quickly dissolve and eat away the glove finger tips.
One skin protective product I've used time and again to keep my hands clean is Invisible Gloves #1211, a water soluble hypoallergenic pomade. I rub it into my hands BEFORE I even think of touching a paint can. Since the pomade is water soluble, you must resist wiping a perspiring forehead with your hands or getting your hands wet, because the moisture will dissolve and ruin the protective coating.
Although MEK, zinc chromate, epoxy, and aviation gasoline won't penetrate the protective barrier on my hands, water will. I am always surprised how easily paint smeared hands cleanup with soap and water. Resist the temptation to clean your hands with lacquer thinner, or MEK, as they are harmful to your skin. The fumes aren't so good for you, either.
Workbench Surfaces Get Messy, Too
You have to mix the paint somewhere. The workbench is an obvious first choice. It is inevitable that you will spill paint trying to pour it from the paint can into your mixing pot. Then, after the paint is mixed you will spill even more trying to fill the spray gun through a paper cone paint filter. For that matter, you may overfill the spray gun because you can't see through the paper filter, and there it goes all over the bench.
What can you do to minimize spills? Not much. Just be as careful as you can. Keep a roll of paper towels handy and use them frequently to wipe up the spills as soon as they occur. This will do much to minimize the mess of cumulative paint spills. These acrylic enamels dry fast so you better wipe up spills as soon as you can.
Before starting any paint work it will be worthwhile to spread and staple a heavy plastic sheet over the work surface area where the paint mixing is to be done. Then, whatever spills do occur will not soak into the underlying wood surface and can be easily wiped away. By the way, how many painters have you seen wearing a respirator while they were mixing paint? Those fumes, you know, are no less toxic than the fumes given off while spraying.
You Are Going To Paint It . . . Where?
In the driveway most likely. However, you will learn quickly that you are taking a chance when you decide to paint your airplane in the driveway. Painting under trees is even chancier because you will have to cope with falling leaves and buds, bugs and strafing birds, as well as airborne dust particles. Such a decision means, at the very least, you will need to erect some kind of overhead cover . . . say, a temporary plastic roof spanning your work area. The plastic cover can be stapled to a simple wood frame or you might consider making the structure with PVC pipes, T-sections, elbows and flanges. In that case, the plastic would have to be taped to the pipe. Fortunately, both duct tape and masking tape stick tenaciously to the plastic sheet so don't worry about adding staples or other fasteners. Consider the effect these prospects could have on your work:
1. Should you have a day or two when it rains, that plastic roof will fill with water and may even collapse the light frame.
2. Strong winds might blow it away.
3. A plastic roof won't keep the dust away from whatever you are painting.
Oh, well, you can't paint when it is windy or raining, anyway. The ideal setup, of course, is a completely enclosed plastic shelter with filtered air inlets and effective suction fan outlets. Such a temporary enclosure could be set up inside the workshop (garage), or just outside the door in the driveway. It means extra work and expense but it might be worth it under some climatic conditions.
To thwart bugs and flying insects, plan to paint only during the early morning hours. There will be little or no wind (usually) and the humidity will be higher providing a potentially dust-free few hours. To this end, I usually turn on the lawn sprinkler system and, also, wet down the driveway.
A word of caution, however. If you are doping an airplane with a regular spray gun, realize that dope does not take kindly to a high humidity (65% or higher) and the doped surfaces could blush. A high humidity, on the other hand, is not a problem when using a HVLP gun as the turbine heats and dries the air passing through the spray gun. Incidentally, avoid spraying any component that is in the direct sunlight as its abnormally heated surfaces will affect the paint behavior and paint flow-out.
Overspray, a Serious Problem
Spraying your airplane under the plastic roof of that makeshift driveway shelter has other ramifications. The paint overspray will easily carry 50 feet or more. Any object within that distance will receive a barely visible mist coating from the airborne paint. This includes nearby autos, bicycles, boats and shrubbery, too.
Protect Everything You Don't Want Painted!
Protect the floor/driveway pavement beneath the components you will be painting. If you don't, the ground will gradually assume the same hue as your airplane. Plastic sheets spread over the ground (pavement or floor) where needed, although unsightly, are effective. Always keep in mind the awareness that while you are concentrating on the component being painted the overspray, in the air all around you, is settling on everything nearby.
Even more devastating, the components or parts you have already painted and put aside may now be gathering some of the overspray, too. Consider this as an important precaution. As soon as you have painted a part, remove it from the area if you intend to continue painting other parts. Anything nearby that you don't want coated with that almost invisible overspray must be draped with protective plastic sheets. But be absolutely sure the parts you cover with plastic sheets are completely dried or the plastic covering may stick to the finish.
Look At Your Shoes, Man!
You may not realize it but your shoes will also surely become victims to overspray from the repeated use of the spray gun. Select the worst pair of shoes you own and wear them every time you paint. By the time the airplane is completely painted, you won't feel so bad about getting rid of those comfortable old paint speckled beauties.