ID:Tony Bingelis •

ILT

NO MATTER who will paint yourairplane - or where or under what condi-tions - the final results can only be asgood as your own pre-painting prepara-tions will make it.

When you first begin thinking aboutgetting your airplane ready for painting,you, like many of us, will probably under-estimate the size of the job. It will re-quire more than a little bit of sandinghere and there and a coat of primer toprepare it for its final top coat.

We soon learn that simple jobs oftenhave a way of mushrooming into full-fledged time consuming projects. Un-fortunately, preparing an airplane is asimple enough task but it seems to goon and on. That being the case, it isadvisable to begin your pre-paint prep-arations somewhat sooner than youmight have anticipated.

A good time to start preparing yourairplane would be coincident with theinitial assembly of the airplane.

Typically, an initial assembly of thehomebuilt is made soon after all of themajor components have been com-pleted.

This preliminary assembly effort isprimarily for the purpose of rigging thecontrols and assuring yourself that ev-erything fits.

As you install each of the control sur-faces, for example, you will have to es-tablish that it connects properly, has therequired range of movement and thatsufficient clearances are maintained.

While doing all this, you may find thatyou have to adjust clearances by cuttingaway more metal, enlarging openings,and smoothing and fairing some of theedges. Small details like this affect thefinished appearance of the airplaneconsiderably and are best corrected onthe spot lest you forget them later on.

These distracting little chores ofsanding, filing, trimming and patchingcan develop into a lot of work but theyhave to be done to assure yourself thateverything looks good, fits good andworks good.

As you get further into the preparationof the external metal surfaces, the de-tails requiring attention sometimesseem to be endless as one blemishafter another is discovered. Unfortu-nately, you cannot rush the work orslight the smallest detail. Yes, it will taketime, a lot of time . . . maybe weeks.

PartiPreparing It For PaintingYou might be able to complete your

preparations for painting the airplane inas little time as a week or so - but Idoubt it.

There is good reason for my skepti-cism. Although the paint may cover thesurfaces uniformly, it does a very poorjob of concealing surface imperfections.Does seeing scratches and sandingmarks under a paint job bother you? Ifso, you'd be much happier to see yourairplane free from that sort of eyesore.If uneven or rough edges seem to jumpout at you when you examine otherairplanes, resolve that your own projectwill not suffer from like problems. All ittakes is a little extra time and a lot ofelbow grease to eliminate these andsimilar blemishes.

Look For These SurfaceImperfections

Here are 10 of the most commonblemishes that detract from an other-wise beautiful finish:

1. Sanding scratches, swirls, and filemarks.

2. Pin holes in fiberglass compo-nents.

3. Bumps, lumps and buckles in thesurface metal.

4. Poorly driven rivets.5. Poorly countersunk holes and im-

perfectly dimpled holes.6. Misdrilled holes.7. Rivet gun marks and other dents.8. Irregular or unfinished edges,

joints and gaps.9. Poorly fitted covers, plates and trim

strips.10. Inadequately cleaned surface

(ink markings, etc.).Unfortunately, the crowded confines

of our workshops, as well as the relent-less passage of time (two, three or moreyears for most projects) often subjectsa project to a variety of cosmetic mis-haps that can best be described as"hangar rash."

Useful Preparation Tips

The so-called hangar rash not-withstanding, unless you are an excep-tional builder, a fuddy duddy as it were,you will certainly be surprised by thenumber of previously unnoticed littleblemishes and skin problems you arefinding.

If a beautifully finished surface is im-portant to you, everyone of these flawswill have to be corrected somehow.

A few suggestions follow.1. Reworking Unsightly Blemishes

and Damaged Areasa. Sanding - Thoroughly examine all

of the external surfaces, inch by inch,

You can prepare, prime and paint both sides of a wing panel this way . . . without anyhelp. Suspend the wing from its aileron bracket with a wire to a screw hook screwedinto the garage door frame. Rest the spar end on a saw horse or stand.

SPORT AVIATION 29

for deep scratches and file marks.Having used too coarse a grit

sandpaper may also have contributedto some scratches. These will certainlyshow through the painted surface un-less you remove them. If the scratchesare fairly deep, fair them out with No.240 grit paper. Then, sand the affectedareas with No. 320 grit wet/drysandpaper followed by the smootherNo. 400 grit wet/dry sandpaper. Do notremove any more of the Alclad finishthan is necessary to remove thescratches and other blemishes.

Water sanding is the fastest, cleanestand easiest way to sand. If you can,use a water hose adjusted to provide atiny trickle of water at all times. If thatis not possible, a pail of water and asponge will serve almost as well. Wetthe surface thoroughly before you startand work in the shade, if you can.

The correct sanding technique callsfor the sanding to be done in straightstrokes. That is, sand with straightstrokes in one direction (back and forth)or alternate with cross hatch strokes.

Never sand with circular motions. Theswirl marks are more likely to showthrough the final finish.

b. Rivets - Examine each rivet for fit.Rivets should be seated solidly in theircountersunk or dimpled holes.

If a rivet head is slightly cocked orprotruding, you should file it down, ordress it flush with a rivet shaver set inyour Micro Adjustable Stop Countersinktool.

To do a good job of inspecting rivets,run your finger tips over each rivet tosee if it needs special attention. You willbe surprised. Your finger tips can tellyou a rivet head is protruding or other-wise needs attention when your eyesalone won't even see the need.

Replace poorly fitted solid rivets if youcan.

If the rivet is sound but poorly driven,

A fiberglass fairing at the base of a windshield should be faired and primed with asandable primer. Any pin holes that become apparent can then be filled by smudgingover them with your finger wetted with primer.leave it be and fill around the blemishwith a filler (lightweight Bondo or simi-lar) after roughing the spot with acoarse grit sandpaper.

Hammered dents and depressionsadjacent to rivets (known as 'smilies')should be similarly filled and leveled(after roughing the area with coarsesandpaper). After filling the ding, dressthe Bondo filled area roughly with acoarse file (clean the file frequently) be-fore the filler sets too hard.

After the filler cures completely it be-comes so hard that sandpaper cannotdo a good job of leveling it and feather-ing the filled edges.

Finally, scrub around the rivet headswith a toothbrush dipped in acetone,MEK or lacquer thinner, especially ifyour rivet holes have been primed andthe wings and other metal componentshave been laying around for a year ortwo. If you don't, the finish coat may notflow properly around inadequately

Sanding and scuffing the fuselage bottom is tiring work. It helps to have a creeper tolie on ... but don't stop to rest or you just might doze off.30 SEPTEMBER 1990

cleaned rivet heads.c. Lumps and Bumps - Carefully re-

move all previously overlooked har-dened glue and resin drips. Theselumps and similar drippings cannot usu-ally be dissolved by solvents, so youmay have to remove them mechanicallywith a sharp wood chisel or a singleedge razor blade. Be careful not togouge the soft metal surface. If a par-ticular lump cannot be sheared off, workthe lump down flush with a shop file.Finish the clean up with sandpaperwrapped around a sanding block.

Never try to dress down a lump withsandpaper backed only by finger tippressure. You will find that thesandpaper will tend to override theblemish and cause you to inadvertentlysand off more material surrounding anoffending lump than from the lump.

A small protruding bump in the metalis best left alone. You can't file or sandit down without cutting through themetal. If you want to risk it though, youcould try hammering it down and chang-ing that bump into a depression. A de-pression can be filled and leveled. How-ever, this won t work if the bump is di-rectly over some underlying rib or struc-ture. Anyway, think hard . . . is it worththe risk?

d. Fiberglass Parts - Most metalhomebuilts use a number of prefabri-cated fiberglass components. Some ofthese are beautifully finished, others arenot. Anyway, these fiberglass parts arenotorious for harboring countlesspinholes that seem to show up onlyafter the parts have been primed andpainted.

What to do? I would suggest you firstmake any necessary repairs for exten-sively gouged areas, separated joints,or other imperfections, using fiberglasscloth and resin.

If the area being treated is not large,only a filler is required. You can usemicroballoons (Q-Cells) or preferably alightweight Bondo filler for small areas.

Next, sand and smooth all of thefiberglass seams and edges (wing tips,cowling, fairings, wheel pants, etc.) witha sanding block. Finish with No. 320 gritsandpaper. Blow off the sanding dustand wipe the surfaces down with a sol-vent.

Follow this by spraying the entirefiberglass component with a sandingprimer like "Fill 'n Sand" (DuPont) orsome other similar brand.

That primer coat will, magically,cause pinholes and other imperfectionsto stand out in stark relief, making themmore visible.

Unfortunately, no matter how muchprimer or paint you spray over these tinyrascals, you cannot hide them. All youwill be doing is to cause a heavy buildup around the pinholes, making themshow up worse than ever.

The only practical way to fill pinholesis by smearing primer on your fingerand rubbing it over and into the holesto seal them.

When you think you have covered allthe pinholes, sand the treated area,blow off the dust, and wipe the part witha clean rag dampened with an enamelsolvent.

Make another inch by inch inspectionand again try to fill the newly discoveredpinholes.

Although you may carefully checkand check again, don't be surprised ifyou discover a few more pinholes . . .AFTER you have painted everything.

e. Metal Edges and Clearances - Besure the clearances around your controlsurfaces are adequate and there is nodanger of them rubbing or bindingagainst adjacent structure.

Smooth and slightly chamfer theedges with a smooth cut file to finishthem.

Your gaps and joints will look muchbetter when their adjacent edges areuniformly parallel to each other.

Working a hand held hacksaw bladedown, along and through each joint willhelp even their edges.

For example, the joint between thecowling and the firewall, as well as thespace between the upper and lowercowling halves, can be noticeably en-hanced by running a hacksaw blade be-tween the edges to even them up. Care-ful . . . don't saw into the underlyingpiano hinge or adjacent parts.

All metal edges, particularly thoseforming the ends of the flaps and ailer-ons, should be dressed with a file tomake them smooth and straight. At thesame time slightly round the edges.Sharp square edges and corners do nothold paint well and chip easily.

After you have filled, filed, sandedand otherwise repaired whatever dingsand unsightly gouges and scratchesyou can find, your wings, fuselage, con-trol surfaces and tail assembly can bereadied for priming.

2. Preparing Metal SurfacesFor Priming

As you know, primers are undercoatsapplied to metal surfaces to inhibit cor-rosion and to provide a good base forthe application of paint (polyurethane,lacquer, enamel, etc.).

NOTE: Never ever spray paint (or forthat matter, primer) directly over an un-prepared Alclad aluminum surface. Thepaint (or primer) will peel or flake off.

Before you can prime Alclad alumi-num surfaces and be assured that theprimer (or paint) will not peel off, theymust at least be:

a. Scuffed with Scotch Brite (3M)pads, or

b. Sanded lightly with No. 400 gritwet/dry sandpaper.

The purpose of the scuffing, or sand-ing, is to de-glaze the Alclad skin. Thiswill provide a slight "tooth" and theprimer will adhere better.

This procedure is considered to bethe first step in preparing new aluminumsurfaces for priming.

This scuffing or sanding can be donewet or dry. Some builders use theScotch Brite pads dipped in water al-though you may prefer to use them dry.

To speed up your scuffing work andto cut down on the manual labor, tryaffixing a Scotch Brite pad to your jitter-bug (vibration) sander.

After the entire surface of a wing (orwhatever) has been dulled, blow off thedust with an air hose while wiping thesurface with a clean rag. Following thedulling process, you have two alterna-tives:

Method 1 - The low cost minimumeffort method.

a. Wash the scuffed skin surface withsoapy water. Then, rinse, wipe andblow dry the joints and corners with anair hose.

b. Spray on a coat of zinc chromateprimer, preferably a self-etching primerlike Variprime (DuPont product) and thesurface is ready to receive its finishcolor coat.

This is considered to be the minimumpreparation method. So much for thebare minimum preparation.

Method 2 - The 2-step Method.This is a more expensive preparation.

It is also considered to be the aviationindustry standard for preparing alumi-num surfaces for priming.

For example, the DuPont paint folksrecommend using their 2-step cleaning/etching preparation.

Step 1 - Clean the surfaces with their225-S Cleaner.

Step 2 - Apply their 226 ConversionCoating to the cleaned surface.

After that, the surface is primed, mak-ing it ready for painting.

The Ditzler paint folks also recom-mend a similar 2-step preparation treat-ment of their own. That is, after thebasic scuffing, the aluminum surface isto be treated with their DX-53 Alumiprepcleaner and then given a DX-503Alodine conversion coating.

Actually, other well known paint com-panies have their own 2-step procedurefor preparing the bare aluminum skinsfor priming and painting. Use whateverbrand you like, but for the best resultsstay with their products all the way . . .and follow their instructions to the letter.It could keep you from Part 1, botchingyour paint job.

For example, did you know that paintmanufacturers usually stipulate that a

Rest the propeller hub on a saw horse and you will have easy access for preparingthe priming the bottom of the fuselage. Don't forget to chock the wheels.

SPORT AVIATION 31

The engine mount finish suffers unbelievable abuse during the installation and hook-up of the engine. Use a good epoxy primer. Enamel or lacquer finishes scrape andchip easily. By the time you finish, the mount will look like it has been hit by shrapnel.

The primer and paint will not adhere very well to an Alclad surface unless it is firstdulled by scuffing with a Scotch Brite pad or with #400 grit wet/dry sandpaper.

primed surface be given its finish coatwithin so many hours or days after theirprimer is applied?

Many builders prime their completedcomponents and store them for monthsbefore they can be painted.

These old primer coats need to befreshened by a light sanding with No.400 grit wet dry paper and wiped downwith an enamel reducer, or be given aseal coat. It all depends on the type ofprimer used and the manufacturer's in-structions.

After all those long drawn out days ofsurface preparations, it is nice to knowthat the whole airplane can be paintedin a mere day or two. However, that, ofcourse, depends on the complexity ofthe color scheme and the type of paintsystem to be used.

You know the rule. When all elsefails, read and follow the instructions.

More next month.

If you wish to contact the authorof this column. Sportplane Builder,for additional information, pleasewrite to Tony Bingelis, 8509 Green-flint Lane, Austin, TX 78759.

If you have to prime and paint your airplane in the driveway, pick a cloudy day.Painting in the sun is not recommended. The surfaces get overly hot, and shadowsmake it difficult to get even coverage with the primer or paint.32 SEPTEMBER 1990

BOOKS BY TONY

The following books by Tony Bingelis areavailable from the EAA Aviation Foundation,EAA Aviation Center, Box 3086, Oshkosh,Wl 54903-3086,1 -800/843-3612, in Wl 1-800/236-4800. Major credit cards accepted.

- Sportplane Builder (Aircraft Construc-tion Methods. 320 pages) - $17.95.

- Firewall Forward (Engine InstallationMethods, 304 pages) - $19 95

- Sportplane Construction Techniques(A Builder's Handbook. 350 pages) - $20.95.

Add $2 40 postage and handling for eachpublication ordered .or order all three for$52.97 plus $6.95 postage and handlingWisconsin residents add 5% sales tax.