Building

Painting Model Airplanes with Urethane Paints

Doug Moon

Dallas, Texas

I would like to preface this with a simple statement. This method is not set in stone and there are many different ways to paint with Urethane paints and get the same results. These are the steps that I have found over the years that help make it easy and quick to get a good looking high gloss finish in just a few short hours.

The product I use is DuPont ChromaBase paint and DuPont ChromaClear.

Finishing with urethanes can be very easy quick and rewarding. I used SIG Nitrate dope as my under coat. Used this to prep the wood for covering and sealing the surface. I like SIG nitrate dope it is light and easy to work with. I always use SIG thinner when using SIG dope.

From bare wood I apply 4 coats of clear dope thinned 50:50. I sand between the third and fourth coat. Also I sand after the fourth coat. At this point I apply the covering I am going to use. I use PolySpan on open bays and carbon fiber mat on the sheeted wood areas.

After the four coats of dope the PolySpan was then applied with 90% thinner 10% dope mixture. The thinner penetrates well and activates the dope underneath and it sticks great.

After the covering is applied I brush down 2 coats of dope, thinned 50:50, over the entire airframe. Then sand out smooth. It works very well. I brush down three coats of 50:50 dope over the Poly Span it takes more dope to seal it. Then sand smooth. Do not cut into the PolySpan. Just cut the dope off of the top and move to another area. It will not feel as smooth at this point as say silkspan would. It will fill very easy so don't worry.

Next comes the filler. I use Zinc Styrate(sp) and nitrate dope. This is extremely light and can be spayed on and sanded off many times with very minimal weight gain. I used two coats on my last plane and it was ready for a guide coat of filler. I used the English Color house auto primer with their standard lacquer thinner. This is a great product and pretty much the same wherever you go. The primer dries extremely fast and can be wet sanded in just a few hours after application. This primer is very heavy so please be very careful when using it. I mix it 1 oz of primer to 5 oz of lacquer thinner. This is a very hot solution so have your canopy and other plastic parts that are attached to the plane covered very well. I double up on the tape on my canopy to keep it (thinner) from taking of the dye. I spray this stuff on very lightly and use it as a guide coat only. It will show where I have not fully filled in the areas. It will build up in layers so you can do your final filling with this mixture. With this much thinner in there it dries in about 10 minutes and can be sanded out in about 20 minutes. I like to sand and apply again to the area in question and see if it flat enough. With the fast drying solution you can do it all in one evening.

Once your surface is up to your satisfaction the fun starts. You should probably think of a paint scheme ahead of time. This helps when applying tape and trim and letters. So you should head down to your local sign shop and have some stencils cut out of the name and numbers you want use. All the letters numbers and such have to be painted for the best results. Be careful the sign shops vinyl is very sticky and can rip covering when pulling it off. You can also cut your own stencils out of friskit paper or Gerber mask. I prefer the Gerber because it is very low tack and pulls off with no complications. I also use a hair dryer and lightly heat it when pulling the mask and tape of any kind off the plane. This will help release the adhesive. I buy Gerber Mask by the yard and take it to the stencil shop and they cut it how I like it for a very small cost. You can also cut your own out of it with the trusty old no. 11. Reese Supply here in Irving Texas carries it. You can look them up and they will sell you what you want. They are a supplier for sign shops. I am sure there is a supplier in your area.

Now clean off your table and get ready for a day of painting. The colors I used on my latest Bear were 2000 NASCAR red, black, and 1997 Corvette Blue. The really nice thing about these paints is you can get a chip of a color and they can match it. Or you can pick from their book of literally thousands of colors.

Prior to painting wash your hands. Now wipe the plane with a tack cloth. This will remove any dust that is still laying around on the surface. I have never used prepsol or material like that. Wiping the plane with liquids like that scares me and I advise against it. Between each coat I wipe with tack cloth.

The paint is sprayed between 30 and 40 psi. I have found lately that I can spay with as little as 20 psi. I would recommend using the prescribed amount of pressure. Also a touch up gun is the gun of choice. Mine was about 40$ at Home Depot. The clear is sprayed a 40 psi do not deviate from this setting.

You should also purchase a good painting mask they are about 30$. You should never spary chemicals of any sort without one. If you do not use a mask you will end up with an upset stomach, light headed, sick, and some harsh chemicals in your lungs that don't go away. Do not take this lightly no model is worth your health. With a good mask and a well ventilated working area all this is not a factor. You should also cover yourself. Wear a cap or baseball hat, rubber gloves the thin dr. gloves work best, long sleeve shirt and pants. Protective eyewear is always recommended.

You need to know that this paint (the paint that will be seen) cannot be color sanded before clear. The sanding strokes will show and you will not be happy with the end result.

After you are fully satisfied with your final coat of primer it is time to paint the main color of your paint scheme. Now if you are planing on one color and just some highlight lines or numbers and letters only, go ahead and paint the entire aircraft the color you have chosen. In my case I was going to paint the entire tail section and the nose red. I taped off the tail and the back half of the fuse and the nose so I would not be painting over an area that does not need the color. This is back masking. (this is how the pros keep it really light) This also saves paint. The colors I choose are not cheap. The coverage is so good that I will have these colors for along time. The shelf life is in the average of 4 years. I have used paint as old as 6 years and had no problems. Now I have the entire aircraft except for the tail section and the nose 1997 Corvette blue.

Now after about 30 minutes I tape off the front half of the fuse and the nose paint the entire tail section and the nose 2000 NASCAR red. I wait 10 minutes and remove the tape. At this point I am smiling because I can see it all coming together. I have been working about 4 hours since I started painting.

Since I already have red mixed up I lay down all of my stencils that will be painted red. In this case it was all the letters and numbers on the wing were going to be red. I put down the stencils taped all around all the edges to keep over spray off. Spray the color. Wait 15 minutes. Check and see that the red is covering the blue all the way. This may take two or more coats. This is the case with any light color going over a dark color. It doesn't matter what you are painting with this will be the case. After I am satisfied with the coverage I pull the stencils 15 minutes after the last coat is applied. Do not leave stencils on for longer than is needed they will end up stuck to the plane. As soon as the paint flashes and appears dry to the eye it is time to pull the stencils. This goes for pulling tape also. Usually when the paint dries it will begin to try to pull the tape up so if you have to go for a second coat be sure to check in the tight corners where you have tape applied or in a curved line. Just lightly press it back down and paint on as usual. Red does this more so than the other colors. If you know to look for this it is really no big deal. If you should forget you might see some over spray in the tight corners where there were some real tight curves. Just keep your eyes peeled.

Now I change to the Blue and paint all my stencils on the tail section. This is a small area so total work time is very small. It is blue going over red so it covers in one coat. I am done in about 1 hour. I am sure this can be done faster. I don't do this for a living so I just take my time and work slow to minimize mistakes.

Now comes the tough part of my paint scheme. The Moon eyes from Dean Moon racing products. There is no stencil available so I cut my own and do some pretty wild looking masking around the area in question. I used white and black for this part.

These two colors were painted with an airbrush. The airbrush is not recommended for this paint. Since we use such small areas it is okay to go for it. The real reason they don't want you to use it is uneven coverage. I just gave it enough pressure to pull the paint out of the tip and it covered nice and smooth. I put the white part down first. It took three coats to cover the blue. Then I put down the black part. I took only one coat. I finished with the black on purpose.

I moved to the nose of the plane. I was going to put a set of twisted checkerboards on the nose, black over red. I taped the checkers off and one coat later presto a perfect set checkers on the nose. Now I am going to paint some thin black lines along the leading edge of the wing and the stab. I taped it off and 30 minutes later the lines are straight looking good. It was nice having the black already mixed up in the airbrush.

Now I let the paint sit for about an hour.

I come back after a sandwich with freshly washed hands and wipe the plane off with the tack cloth twice over the whole airplane. Once I feel it is clean enough I move onto the clear coat. I uncover the canopy, I previously sanded it with 1200 grit to get it real smooth. Yes spray the canopy it will come back very shinny.

Remember there is no sanding prior to clear. You want to touch the plane as little as possible. I wear rubber gloves at all times during the finishing process. This will keep all oils from your hands off the plane.

When it is clean shoot the first coat of clear. I recommend going for a dry coat. I have heard the terms dry coat and wet coat since I got into this Painting airplane stuff. It was a while before I really knew what they were talking about. Well on the touchup gun there will be a mechanism (big screw) that will adjust how much product is being sprayed with the given amount of air. The more you turn it one way the more air there is and the more you turn it the other way the more product comes out. You really can't see it in the air but you can when you apply it to something. I suggest you test on something and get it how you like it before you go for the plane. If this is your first attempt at spraying the dry coat will look rough like very fine sandpaper. It will also dry faster. Move the gun evenly and smoothly along the air frame staying the same distance away from it all times. There will be over spray on the plane in some places. This is hard to avoid with dry coats. Now I let this dry for at least three hours. I now have close to ten hours total time after the three hour dry time. I give it this long so that I can knock off some the over spray before final coat.

Now comes the hardest part of this whole process. I recommend if it is late that you go to bed and do it tomorrow when you are completely rested. If you feel fine after the three hour rest go for it. It will only take about 20 minutes to put down the final coat. If it is dry enough to knock off over spray then you can wipe it one more time with the tack cloth.

Now mix it up just like the can says set the pressure at 40 psi. Do some testing on a board or something smooth. You want this coat to be wet almost wet enough to run. Take your time get it right on the smooth board or what ever you have decided to test on. I usually finish a piece of wood along side of plane for this very step. Now go for it. Put down a smooth coat. Spray the edges first then the flat areas next. One thing that you will notice is that the wet coat will absorb over spray very nicely. It will look like over spray then when you come back later it will be gone. This is called "wetting out." If you are getting this result you are right on the wet/dry mixture. If it won't absorb most of it then you might be too dry. Of course if it runs you are too wet or have too much clear on it. Important; if it does run you cannot wipe the run away like you can with older paints where the clears sits on top of the color. This clear actually attacks into and activates the color so if you wipe a run you will smear your paint underneath. Just get away from it and clear elsewhere and sand it out later. I got big runs on my cowl but I sanded them out later. Once the coat is smooth and wet stand back a smile at what you have created. The really cool thing as that once you put it down wet it dries looking wet. What you see is what you get.

When you purchase your clear coat it would be a very good idea to purchase a can of reducer. This is the equivalent of thinner for lacquer. This clear system cannot use thinner so they have their own stuff called reducer. The clear, by nature is thicker than water and dries very fast. It can be difficult to get it to "flow" out of the gun smoothly. With 10% reducer added it is a dream. The reducer will slow the drying time and the "wet out" is incredible. It helps to thin down the mixture and it will cover in very smooth thin coats. This is a small purchase that can really make this enjoyable.

The paint job is done.

At this point if you want you can blow off buffing it out if it is shinny enough.

If you do plan on buffing it out you will need to wait at least eight hours for the clear to fully cure. I would recommend a full twenty-four hours before starting the quest for the ultimate shine. Always check with you supplier about buffing and how long you should wait to sand it out.

Buffing urethanes is no secret. Wet sand the surface down with 1200 grit paper. Change your paper often for best results. You can go as rough as 1000 but do not go any rougher then that. If you do the clear is so hard it will lose shine. It is called cutting the shine out. The paint store guys will tell you the same thing. After the whole plane is sanded evenly with 1200 come back and sand it out with 2000 wet.

Now you are ready to buff. Buy 3M Perfect It-II compound and polish until you get a good shine. They may have a new compound for it by now. I bought this stuff two years ago. They always seem to come out with new material to improve the process. I used a machine buffer on my last plane and had the whole thing polished in two hours. The sanding of course took longer than that. For the best results an orbital buffer that spins 2000-4000 rpms will bring out that mirror shine like never before. If you do it by hand it will take longer that is all. Just keep rubbing until it shines. If you do buff and sand it out I suggest doing it within one to two days of painting it. If you wait to long the clear will be so hard it will not buff out. The compound will not cut it. If you clean it with Windex or any glass cleaner and the shine wipes off you have not buffed enough. Just keep rubbing.

I hope this helps. If you have any questions just call or write anytime.

I always love to talk airplanes.

Stand back and smile.

Doug Moon

Covering with Plastic Film

by John Miller aka JoeBellcrank

Since there are many ways that will work with film covering, I thought that I'd offer a few that work well for me.

Why Plastic film covering may be for you.

First, let's explore why you might want to use a plastic film rather than the traditional Silkspan, Polyspan, dope, or painted finishes. Let me say right up front, that a well executed "Kote" job can really look good, but they usually will not match up to a well done traditional finish. Still, you can expect to get decent appearance points, without all the fuss, and time invested in a painted finish. Plastic films can be a long lasting, serviceable finish with proper application and care. I use them often because I live in an Apt. My neighbors appreciate having less dope smell wafting through the complex, and not having to listen to a compressor.

Another possible advantage is a well done film finish will often weigh less than a painted finish. It will also often take less time, which allows you to be out flying, trimming, and practicing, while the other guys are still painting their planes.

Tools required.

Might I first suggest that anyone new to plastic film covering, get the excellent book on the subject by Higley. Becoming familiar with the techniques as discussed in this book will form a good basis for what I'm going to have to say on the subject. A little study with a book such as this will shorten your learning curve.

I'd also suggest, that if you are absolutely new to film coverings, that you try the various techniques on scrap pieces, and built ups that simulate specific problem areas we'll be discussing. The bare minimum tools required, won't set you back as much as it would if you were trying to do a good paint job. I would suggest the following to get started.

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A 100 pack of single edge razor blades.

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An exacto knife.

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A bulk pack of no. 11 blades for the Exacto.

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A covering iron.

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A covering heat gun.

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Several pieces of poster board. (used under the covering when cutting.)

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A can of Balsarite, or Sigs "Sticksit".A foam brush to apply the Balsarite.

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A good light source. (It's always easier when you can see what you are doing.)

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Several straight edges, in different lengths.

Additional, or optional items that will make it easier to do a superior job.

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An extra iron with a covering sock.

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A small trim iron.A trimming tool.

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A self healing cutting mat.

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Friskit "rotary" cutters, straight and pinked.

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A good pair of scissors.

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A smoothing glove.

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Several pieces of foam or a couple of blankets to lay on the table to protect the plane and your prep work from damage while you are working on covering it.

Which plastic film covering?

Let's look at the available film coverings for a moment. There are a lot of choices out there, but I would suggest that you only consider the top of the line coverings. Your job will look better, and last longer by using the best. Some of the low temp shrink films will look good for a while, but my experiences show that there's often a delamination that occurs between the clear plastic, and the color/glue over time. Money spent on the best films available, will be money well spent.

My own films of choice are, MonoKote, Coverite Mica Film, and Oracover, or it's successor Ultrakote. These films seem to be much stronger, and longer lasting than the "Econo" brands. Of course, if you're covering a plane that will be used in any kind of sport, combat, or other events where appearance isn't as important as PA, go ahead and save some bucks if you want.

Covering a stunt ship is different.

Most CL stunter film coverings are limited to the flying surfaces, with the fuse painted. This is a good compromise for PA. A bit of attention to the wing/stab/fuse joints will make the change almost seamless. It's also possible to completely cover profiles and full fuse ships with a film. I'll try and cover the methods for both.

Preparation.

In any method of finishing, preparation is always the key to a good finish. Film covering is no exception. Proper sanding of the base is essential. Sand as if you were planning to do a traditional covering. Be sure to use a tack rag prior to apply any covering. Small imperfections will show like a boulder under a film covering. Remember, the covering is the final finish. You won't be able to sand out any imperfections while you are applying the finish as you can with paint

Straight, or traditional film covering.

The traditional film method, would have you apply the film right over the prepped bare wood. This will work, and give a decent workable finish in most cases, but later I'll outline a better, in my opinion, method. One of the problems with this method, helped a bit by the use of Balsarite, is the tendency for the film to "bag up", or get wrinkles, when exposed to a heat source, like the sun. Over time, this can make a film covering look pretty bad. Constant attention, and re-shrinking, can help, but often the heat used will cause more problems later, in the form of gassing under the covering, which causes the film to become loosened from the wood. A small pin hole at the edges can let the gas out as you stick the covering down should this happen to you.

I always apply Balsarite and let it dry before applying any film. It's just that added insurance for me. One, or two coats applied with a foam brush will be what's needed. After the Balsarite has dried, another light sanding and tacking will be helpful.

Balsarite, or Sigs equivalent product, Sticksit, should be definitely applied in the nose area to help prevent oil seepage under the covering.

Covering the flight surfaces before or after they are attached to the fuse.

Some prefer to cover the wing and stab before attaching them to the fuse. The most important consideration, if this is your choice, is to carefully mark and leave the covering off in the areas to be glued.

Some who go this route, prefer to cover from tip to tip, and then make, diamond cutouts, in the area where the glue will be applied. There seems to be some merit to this idea, as the additional strength imparted by the covering continues through the fuselage. The diamond cutouts allow the glue to attach to bare wood rather than the plastic film and its' bond to the wood, which, in most cases, is not as good as a wood to wood glue joint.

It can be said that the strength imparted from plastic films isn't that essential. those who feel this way often cover after joining the flying surfaces to the fuse. This is my preferred method, even though I do believe there is some strength added by the covering.

Fuselage / wing / stab joint.

If you're planning on covering the entire plane with plastic film, and your fillets are either nonexistent, or very small, you should first address the important joint where the fuse and wing/stab meet. A bit of attention here will pay important benefits in the future.

If you are using small fillets, use your favorite method to apply them. With no fillets, the job may be a bit easier.

After applying and lightly sanding Balsarite, cut a strip of film long enough to go from the leading edge to the trailing edge, with some to spare, and wide enough to extend at least 1/4" out onto the wing, and up on the fuselage. Start on the bottom. Starting at the bottom surface will hide your beginning efforts, should you make an error. Starting on the bottom also puts the all important lap joint slightly on the underside of the surface, where it's not as noticeable.

In the case of no fillets, crease the film lengthwise. Start at the high point, and use the tip of your iron, or your trim iron with the flat blade, and stick the crease right into the area where the flight surfaces and the fuse join. Work out onto the flat sides of the strip, and seal them down real good. Work your way back to the trailing edge, and forward to slightly wrap around the leading edge. Make sure this area is sealed down tight.

With small fillets, you can omit the crease, and use the curved sealing head, or the back of the tip of the full sized iron.

The trailing edge.

Cut a strip slightly longer than the wing panel, and about 1/4" wider than the trailing edge where the hinges will later be installed.

Iron on the flat first, the roll the edges over, on the top and bottom of the trailing edge. There should be at least 1/8" of covering on the top and bottom of the trailing edge.

The wing and stab.

The wing and stab cover almost identical, so what is said should pretty well apply to either.

Cut a piece of film that's at least 6 inches longer, and wider than the surface to be covered. Don't be cheap and scrimp on this as you'll need the excess to grip as you heat form the tips, and leading, edges.

Turn the plane on it's back so you can cover the bottom of the wing first. Set your plane on your covered table with at least 3/4 of the wing supported. (Here's where those blankets or pieces of foam come in handy.)

With your full sized iron, tack, ( touch with the iron long enough to activate the heat sensitive glue.) 3 or 4 places on the wing panel, next to the center of the strip applied in the joint previously. In the case where you have a small fillet, set the edge where the curve starts, and tack in a similar manner.You want the wing tip free, and hanging over the edge of the table for this step. With your free hand, grip the end of the film, near the tip, and put some tension while applying heat from your heat gun near the wing tip. Continue to pull as the film gets soft from the heat. Instead of shrinking, the film will stretch. Continue with the pulling heating and stretching until you have formed the curves at the tip. This is called heat forming . If you continue to work with the heat gun and stretching until you get to a point somewhat past the center of the wing tip, you should, with practice, be able to make a seam without any puckering at all. The heat forming also slightly tacks the formed tip in place, but it will be necessary to seal it down solidly later.

At the trailing edge, use your free hand and put a little tension at the center of the span. Tack with your iron. Do the same thing at three or four more spots, before moving to the leading edge.

Again, use your free hand, at the center of the excess at the leading edge. Use your heat gun and in a similar manner as the tips, heat form the curve over the leading edge. Start at the center, and work your way to the root and tip. A light rubbing with a soft cloth right after applying the heat, will tack the leading edge into place. You can also stretch a little past the center of the leading edge, similar to the tip.

Once all the heat forming and tacking is done, you can iron the covering permanently into place. Start by tacking between the previous tacks, then go for the whole thing and seal it down solidly.

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At the trailing edge, pay some extra attention to the overlap. Make sure it's sealed tight.

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Use a new single edge razor, or your trimming tool and trim the excess from the surface.

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Turn the plane upright and do the top of the same wing panel, in the same way.

You can either do the other wing panel in the same way, or use your heat gun to shrink the covering tight on the first panel. In either case, when doing the final shrink, work a little on one side, and then the other to try and keep warps from being shrunk into the panel. If you do get any warps, they can be removed with a little twisting and heating later.

Some like to seal the covering to the leading and trailing edge, as well as the cap strips at this point. I don't prefer to do this as it makes it more difficult to remove warps that may occur in the future. I also feel that unless you've done a superior job preparing the leading and trailing edge surfaces, any imperfections in the structure will be more apparent if these areas are sealed down tight.

Flaps and elevators.

Flaps and elevators, when not built up, are probably one of the most difficult areas to do and have look right over time. A careful bit of work here, and they'll look good. Hurry it up, and you'll be seeing bubbles and loose covering sometime in the future. Of course, you've done the normal prep work, sanding, tack ragging, and Balsarite. But there're some additional small steps to do when applying the film.

You will need to cover the pockets you sanded for the hinge barrels. You'll also need to cover the flat ends and tips of the flap. Since I like to have my flaps end with a square 1/8" wide tip at the trailing edge., I cut a strip of film at least 3/8" wide and apply it to this area. I roll the 1/8" overage onto the bottom and the top of the flap or elevator. Seal the edges down tight.

For the flat ends, cut a strip in a similar manner and stick the center and then the entire flat. Roll the excess as you did the trailing edge.

For the hinge pockets, it can be a little dicey. the idea is to stick the film onto the longest flat, then to each side, leaving the overage sticking above and below the pocket. Use your razor and slice the crease, formed when you stuck the sides of the pockets, to the top of the surface. Use your iron, and seal these little tabs tightly into place. Pay attention at the 45 degree leading edge.

Now we can cover the flat areas, best done by once again cutting a strip of film wider, and longer than the surface. Start once again on the bottom surface.

Lay the flap. or the stab, as they cover in a similar way, on a clean flat surface. Lay the film on top, carefully centering the film over the part. Use your iron, sock covered if you have it, in the center of the flap or elevator. Work the covering down from the center, to each side, and out to the tip. The idea is to not trap any of the gassing under the covering as you stick it down. Turn the surface 180 degrees, and in the same way, work out to the root. Be careful with the heat, as you can still get some gassing if you're not careful. Next, we need to do the 45 degree angle at the leading edge. Once that is done, cut and remove the covering from the hinge pockets. trim them tight, and seal the edges well. Turn the surface over, and continue the covering onto the other 45 degree surface. Once you are sure that every thing is stuck down tight, Use your razor, or trimmer, and trim all the excess off.

Turn the part over, and do the other side in the same manner. Flaps and elevators are almost identical in procedure.

Fillets.

This section is used for larger fillets, especially when you are painting the fuse. It can also be used with some minor variations when both the flying surfaces and fuse are film covered. In this case, you will paint the fillet with a matching color. LusterKote works for me in this case.

I like to pink the edge of the covering adjacent to the fuse for this method. I cover the wing as before, then form the fillets. You can use epoxylight, epoxy and micro balloons, leather fillets, or balsa fillets to form the fillets.

Before installing the fillets, take the time to tape a line about 1/8" further onto the wing than the edge of the fillet. This way you won't get glue onto the finished surface of the wing. If you covered your wing before installing it, you would do this also before gluing it into place.

Install your fillets. After the fillets are in place, remove the tape, and re-tape about 1/16" to 1/8" further out. sand the edge to a feather edge.Other than covering the fillet with coating of spot putty, the fillets are ready to be painted.

Covering the fuselage.

If you have chosen to cover the fuselage with film, here is the method to use.

It's important to have all the lap joints going towards the bottom of the plane, as well as toward the rear of the plane. This acts in the same manner as a shingle, and resists oil seepage. The exception here is the nose ring. Stick it into place first. Make it about 1/8" to 1/4" larger than the nose ring itself. Once the flats are stuck down tight, you can make slices every 1/4 inch around the radius, now, stick these tabs down very tightly.

Start on the bottom of the fuse, and from the rear, use the largest pieces you can to minimize the laps.

At all times, try to start in the middle of the piece you want to stick down to avoid gassing the glue with the heat. Once all the bottom is done, roll the edges up the side, approximately 1/4". Make sure the covering is stuck tight, especially at the edges.

The side pieces can now be applied. One piece if possible, but most of the time, I'll use two pieces, with the lap at the high point of the wing. Again start at the middle and work out towards the edges. the trimmed bottom edges are finished off flush with the bottom if possible.

Lastly, comes the top piece. Pay some attention here, as this is what will be seen most of the time. Due to the compound shape of the top blocks, it's best, in most cases, to do a bit of planning before applying any covering. If possible, figure where your trim lines will be going, and make your laps in a place that the trim will cover them.

Depending on the shapes, it's sometimes necessary to do the turtle deck in two pieces with a seam at the top center, running lengthwise. Again, work from the back forward. Make your lap at the back edge of the cockpit if possible. Sometimes it's necessary to use the heat gun and do a little heat forming before ironing the covering down. The downside of this happening is that it will be more difficult to avoid gassing the glue, so be careful. With a little work and some attention to detail, the fuse is done.

Painting the fuselage.

Use your favorite method to prep the fuse for paint. Most paints with the possible exception of water based paints will adhere sufficiently to sanded or scuffed film covering, but the best adhesion comes with paints that are formulated to adhere tightly to any surface. These include Epoxy paints, LusterKote and it's kin, and Enamels. Be careful with these paints as they are not lightweights. Make sure the film covered surfaces are masked off to avoid getting any paints where you don't want it to be.

A better film covering method.

I mentioned earlier that there was a better method to use for film coverings. It will work much better than film on bare wood, won't bag up, loosen, or cause problems down the road.

Pre-covering.

First, precover the flying surfaces with silkspan, silk, or Sig Koverall. Koverall as a precovering is the strongest, and also the heaviest of the options, but the strength is unbelievable.

The chosen precovering should be coated with one or two coats of thinned dope, or better yet, Balsarite, thinned 50-50. The fuse, if you are going to cover with film would be treated the same way.

The beauty of this method allows the gasses to bleed off easily, due to the porosity of the substrate. The film adheres to the substrate, and the substrate stabilizes the film. I have seen planes several years old which have never had their film sag or bag up. They are still as tight and smooth as the day they were first covered. On some of these planes, you have to look very close to tell that they are film covered.

In addition to all this, the covering winds up being stronger than either layer alone. I believe it's a win win situation.

Attaching the film.

The method of film attachment is slightly different than the traditional method outlined above. But it's sufficiently similar, that with a few minor changes much of the earlier techniques will work quite well with it. The biggest difference is when covering the wing panels.

Start by tacking the edges around the entire perimeter. Once tacked, use your iron, covered with a iron sock if you have one, and start in the center of the middle open bay. Work your way out to the rib caps. Iron down the rib cap, and move out into the middle of the next bay. Stop at the last bay next to the tip, and where the center sheeting begins next to the fuselage. We'll still heat form the tip to get the best appearance. Once all the bays are sealed down, add some additional tacks to the leading and trailing edge. Use your heat gun and some tension from your free hand to shrink and form the leading, and trailing edges. The heat from the gun will slightly tack the surface to the substrate. Use your iron to finish sticking the film to the substrate.

If you did it right, it will be stuck to the substrate. there will be no sagging or bubbling. the surface will be smooth, and will stay tight and smooth.

This works quite well over solid balsa surfaces as well. The solid surfaces will be smooth and not wrinkle or sag. Fuselages will also look as good as the flaps if you do it right.

Attention to details.

Another advantage occurs when you do your trim. With the traditional method, one usually either paints on the trim, or sticks colored film onto the base film for the trim. The problem with this is that there is no place for the gassing to go, so bubbles come up and even after the pin pricks and re-sticking, you can always see where they occurred.

With this method, and a little pre-planning with your trim scheme, you can leave areas free of the film, and apply the trim colors right to the substrate. All that is needed is to use a minimum of 1/8" laps. With intricate trim schemes, it's again best to work from the back to the front, as it keeps the laps facing away from the airstream.

Transparent films over these substrates look an awful lot like dyed dope finishes. Weight build up can still be less to about the same as a traditional painted finish.

The finish.

There it is. Most of what I know about using film coverings. I may never make Concours, but I often am complimented on my finishes. I'm sure there are others methods as well as tips from others to add to this, and I hope that some of you find it useful.

The Legacy pictured here has been crashed, pancaked into the asphalt, repaired and is now over a year old. It was covered using transparent MonoKote over silkspan, and the covering is still tight, no wrinkles, bags, or sags. During the crash, a small tear resulted when the force of the impact broke the outboard stab leading edge about two inches from the fuse joint. I repaired the tear using the old method, Ambroid glue.

John Miller

I'm wondering why everything is spinning around?

A Modern Model Finish

Bradley Walker

This article is dedicated to the late Monte Lawrence

who was one of the pioneers of the Wilson finishing method. We will miss you!

This article will attempt to outline a finishing method that can be substituted for the old “dope and tissue” method for finishing balsa models. This method was outlined to me at the 2001 Dallas Stunt Symposium by the Fort Worth finishing guru Bill Wilson.

I have taken Bill’s method and added a few extremely minor twists, but for the most part it is Bill’s methodology and method, and I am just a humble, humble, student of the Master. I could have never figured out any of this stuff on my own.

One thing to keep in mind is that any new finishing method will follow a learning curve on the part of the user and I in no way guarantee that YOU can do this system to Concourse perfection the first time. I can assure you that an expectation of perfection on the first attempt will lead only to disappointment. I know that the doping techniques used by a large part of the control line stunt world have been in development for some time now (about 70 years or so).

I would hope that the modeling community would embrace a method of finishing airplanes that can have a “killer” finish applied in a matter of days (or hours) instead of weeks or months. However, it is still every modeler’s responsibility to understand that any new method will require patience.

This is the method starting with a balsa airframe:

The solid sheeted surfaces are finished with Minwax Polycrylic (PC) and 00 silkspan. PC is available at Home Depot and Lowes and comes in gloss, semi and flat versions. I have always used the gloss version, and I do not know if there are any advantages to the other versions. A quart cost about $10 and will last for several airplanes. Minwax PC has several advantages due to the fact that it is a water based acrylic.

Being water based, it simply has very little solvents and almost no stink. Being an acrylic makes it a UNIVERSAL undercoat for just about any type of acrylic paint (all of the paints used in modeling are acrylic). It dries in 24 hours, and once dried it takes on a character that is very similar to hardened thin CA. Balsa impregnated with PC becomes ROCK HARD (much like thin CA impregnated wood).

It is really not necessary to use any paper with the PC (Bill Wilson sees no advantage to it and he has performed side by side strength tests), but I have found that, for my uses, it is truly wonderful over sheeted surfaces when used with thin silkspan. Using 00 silkspan in conjunction with the PC helps to level the surface at application. To attach the silkspan, first wet the surface with the Polycrylic (there is no need to pre-coat the surface like a dope application). I use the same types of brushes that I use with dope.

WHILE THE PC IS STILL WET apply the slightly water dampened silkspan. Once all the edges have been pulled and the wrinkles are all pulled out, trim the edges of the silkspan. Once trimmed, wet the entire surface of the silkspan with a coat of PC. Make sure to do the entire surface evenly and get all of the edges. At this point it is possible that there may some relaxation in the part, especially for long flat parts like flaps, but no need to worry. Typically, the relaxed parts will return right back to their former shape upon drying. For added security, a good method is to lay the tack free drying parts on a sheet of Teflon on a flat surface and weight down slightly. This will basically guarantee that the parts will dry DEAD FLAT and will not warp in the future. Subsequent coats will have little, if any effect. Let this first coat dry for a minimum of 24 hours and begin DRY sanding the surface with 180 grit ADHESIVE BACKED 3M OPEN COAT paper.

Note on sandpaper: Not all sandpapers perform the same, period. For our uses, except for the case of wet sanding the clear coat, all other sandpapers are severely lacking compared to the auto body open coat papers. The 3M open coat paper can be found at ANY local body shop supply store. I have purchased two different kinds, one is made for air files, it is 3” wide, YELLOW and comes on a roll, the other kind is the 6” sticky back YELLOW DA discs, both are the same paper. Either one will work. DO NOT SUBSTITUTE!!! The ONLY acceptable substitute is the generic for 3M (Nikka). It is EXACTLY the same and costs about $10 less. A roll of 3m will cost about $30 and will last for many, many airplanes and will be the best all-purpose sandpaper you have ever used. If in doubt, buy the 3M, it is still cheap in the long run.

At this point watch for a few different conditions. One, that the entire weave of the silkspan is filled. If it is, you should basically be able to sand all the silkspan wrinkles, edges, and surfaces exactly the same. As opposed to dope, which is simply used to attach the silkspan to the surface, the PC makes the silkspan totally solid. Each individual layer is not longer unique, like when you use dope. The silkspan simply serves as a very thin sponge to accept the liquid plastic. Once the weave is filled the silkspan is fully impregnated with plastic. I use double layers of silkspan over edges that are not quite perfect, fill them with PC and sand it all down flat, so the paper and PC works like a filler.

The PC will sand with some work. Remember it is HARD STUFF, but hard is good for balsa airplanes, especially for a base coat. Second, you will notice that the paper will cut all of the surfaces about the same because the PC has served to make all of the surfaces of a uniform hardness. Glue edges will be the same hardness as punk balsa. This is a good opportunity to do the final shaping on joints and flatten everything out and get rid of the ridges that can appear on edges of dissimilar hardness (I really love this part of the process and I like to spend a little extra time here). Lastly, if you do see an edge appear in the silkspan as you are sanding YOU DID NOT FILL THE PAPER (it will appear white if it is not filled). Re-coat that area and all other dry areas and sand the next day.

For strength, add a second layer of PC and paper to the nose. Re-coat with a third coat after sanding the second coat. The nose will be nice and shiny and ROCK HARD! I have found that the PC prepared nose is harder and more dent resistant than even a nose finished in fiberglass and epoxy, and there is no weave to appear later. It is also a good idea to re-coat at the fillet areas (we have no fillets at this point). Make sure that area gets good and shiny also. This allows you to sand the final fillets without gouging the wood, as the shiny areas will be extra hard. Please don’t go crazy with the PC at this point. One coat of PC is equal to about 4 coats of unthinned dope. Too much all over will add up, so why do it? A fully sheeted plane with two good coats should appear to have a slight plastic look. The nose should absolutely look like it is fully plasticized.

For very small dings during the pre-primer stages I use plain old spackling (not the light spackling). In small quantities I have never had any shrinkage problems, especially when saturated with the PC. For fillets I use Epoxolite or 5 minute epoxy depending on the size of the fillet. Blend sand the Epoxolite on the PC, you will notice the PC hardness will give you more freedom to be aggressive without cutting into the wood, but still watch carefully. DO NOT overcoat the finished fillets with a coat of PC. I have found that PC over Epoxolite is a dicey proposition, so don’t do it! Wait to overcoat the fillets with the primer.

For open bays use medium Sig silkspan or Polyspan (available from Tom Morris) and filled with three coats of nitrate dope with zinc stearate. This is the slowest step in the entire process. On my designs I have no open bays, which eliminates the needs for dope altogether. I have tried PC on open bays, and I have yet to make it work. Bill Wilson does, and he is very happy with it.

Bill’s preferred method is to apply the Polyspan to the open bays using Balsarite adhesive and a hot iron. Once the fabric is fastened to the airframe and the open bays shrunk with the iron, the weave of the Polyspan is sealed with two coats of PC. From that point the rest of the airplane is finished as normal.

The next step is to shoot the entire plane in auto primer. Typically, I use inexpensive lacquer primer surface from English Auto Supply (a local Dallas body shop supply chain). Every auto supply has basically the same lacquer based primer surfacer. Despite the fact that this primer is lacquer based, I absolutely recommend using only urethane reducer in the primer. I only use Omni urethane reducer (this is the same reducer I use in the clear-see below). Omni reducer comes in four heat ranges, which include fast, medium, slow, and super slow. For primer I would recommend starting with medium and thin the first coat 2 to 1 to 1 Â½ to 1 (for over 90 degrees try the slow). The second coat can be thinned closer to 2 1/2 to 1, depending on how much is left to fill. The first coat is sanded dry (DRY! ALWAYS DRY!!! NEVER EVER WET SAND!!!!) with 180 open coat paper. The second coat is sanded with 180 and finished with 320 open coat.

There is really no comparison between the lacquer primer combined with lacquer thinner and the same primer combined with urethane reducer. The less aggressive urethane reducer allows the primer to stack. A stacked surface appears almost shiny and will appear very flat with a very thin coat, also it will shrink less and absorb less weight of the color and clear coats. A stacked coat will also sand like it is very thick even when it is not, and it will also allow the clear to shine more. Faster drying, more aggressive lacquer thinners have a tendency to create a primer surface that is more like a forest of trees, if you will. The trees are all standing up and it takes an incredible amount of material to fill up to the top of the trees. The primer used with urethane reducer is more like a forest with all the trees laying their sides or stacked like bricks in a wall. A stacked surface will fill faster and retain its holdout (the ability of the primer to resist shrinking and swelling at the application of the clear) better through the final coats. Also, the slower reducers will allow the surface to flow out smoother, even though they also require a little more time to dry also (most lacquer based primers are sandable in about an hour).

On my latest plane I switched to the catalyzed PPG urethane primer K-36. All of the primer coats on this airplane were urethane and I only used lacquer primer for fast spot fills. The K-36 is really kind of a hassle to use, as it is only sandable after a full 12 to 16 hour drying time. It also did not tend to fill very well as it tended to wick away from imperfections as opposed to wicking into the voids like the lacquer surfacer. Even though, after all was said and done, there were aspects to the K-36 that I really liked. The holdout was really impressive and it sanded very nicely. It is also very solvent resistant, which can be handy. For the next airplane I plan to use the lacquer primer for the base and the K-36 for the final primer coat.

SANDING THE PRIMER

How to sand filler coats may be the single biggest misconception in finishing. The goal is to obtain a uniform coat of primer. The idea is to get it so thin there is no real weight penalty. If you sand gray auto primer until you can almost read small newspaper print through it, it is PRETTY DANG THIN. I don't care if you shot on your primer an 1/8" thick, if you keep sanding it down until it is uniformly semi-transparent there can't be a lot of weight there.

Applying primer is really pretty simple. Make sure you put enough on to fill every imperfection you can see or you will just end up sanding and re-shooting again. Put on enough coats with the material thick enough to fill. This is a different philosophy than the dust on a coat and sand, dust on a coat and sand philosophy that the dope guys use. As far as the level of fill, your mileage may vary depending on the type of primer used. The PPG K-36 requires 2-3 full coats to fill every bit of the wood grain in a well-prepped model. Lacquer primer surfacer can typically do that in one coat with some spot work here and there. Catalyzed primer does has a shrinkage advantage, which is nice because you hope that all that sanding will be not be in vain once the first coat of clear is applied.

The first part of the sanding process is to block the large flat surfaces. I bust the surface with 180 grit and sand until the very first transparent spots start to appear and then I move on. Sand in larger strokes across the known imperfections as much as possible. At this stage you will start to see the major imperfections (such as wood grain) disappear as you sand. Once the entire surface is done to this level you should see semi-transparent spots periodically but the surface should still be opaque.

Now it is time to remove the 180 scratches, as much excess primer as possible, and bring the primer coat down to a uniform thickness. Switch to 320 and sand all of the more opaque spots until the surface is as uniformly NEARLY transparent as possible. Only sand the opaque areas. Stay away from the transparent areas! You should be sanding in very small strokes or circles at this point and being very specific about where you are removing material. Sanding in long strokes will only serve top break through the more transparent areas. Then, switch to 400 and take the surface down one more level of transparency (this only takes seconds).

At this point there is a layer of primer so thin that 5 more strokes of 400 grit would bust through the surface. You seriously can't get it any thinner. Busting through the surface is a very bad thing, and accomplishes nothing. These areas will inevitably swell with the clear and just show the imperfections. So it does no good to "sand it all off"! This is a huge misconception about the use of primers (including sanding sealer or dope and talc). Sanding the primer until only little slivers of gray are left in the wood grain is not a coat. If you sand this far you have effectively removed the entire coat, so why bother? There must be an unbroken LAYER of primer remaining. I think most would be better served to err on the side of a slightly more opaque stopping point than more transparent. More opaque means there is less chance for dissimilar surfaces, which leads to swelling. The difference in weight in two shades more opaque is most likely not even a factor in the final analysis.

For the color coats use 1 to 1 non-catalyzed polyester basecoat. Common types are Dupont Chromabase or PPG Omni for a good, not too expensive solution. I use Omni, PPG and Valspar (mostly Valspar). A lot of people are truly confused about the function of the basecoat part of the basecoat/clearcoat process. A lot of talk is made of auto clears but there seems to be very little discussion about the basecoat. Simply put, the stuff is really wonderful to work with. It has so many advantages over the dope/lacquer-based colors. One advantage is that it has no gloss binders. Gloss binders create a sheeting effect across the surface that it is applied. This sheeting effect creates the gloss. These gloss binders add needless amounts of weight and are the main culprit for the paint trying to wick underneath the masking tape when applying trim. Basecoat sticks straight down, it does not have any gloss binders so it makes no attempt to stick to itself sideways. The sole function of the basecoat is to apply color, so no gloss is needed. Also, basecoat dries in about 5 to 10 minutes (always use fast reducer) and can be taped on top in that time. We have a saying that you can tape on top of basecoat as fast as you can clean the gun.

Because there are no gloss binders in the color, it is extremely light. There is simply almost no material to add weight. Basecoat is also not fuel proof; in fact, it will wipe away with rubbing alcohol. It is possible to remove an entire color scheme in a matter of just a few minutes with a paper towel and alcohol. Needless to say I do not recommend sanding the color coats, in fact, I don’t recommend touching them if it can be at all avoided.

Basecoat is to be shot dry. The best applications almost look like overspray. This is especially true when shooting taped areas. The drier you can apply the material, the sharper the tapeline will be. Also, dry shooting the material ensures that there is only enough material for coverage. Basecoat does not fill like dope colors, so don’t expect it to. The fill is done at the primer stage, not the color stage. If you shot the color correctly the surface will have the appearance of 400 grit sandpaper, and it will not be shiny at all.

The best thing about auto color coats is that they come in every color under the rainbow. I often pick colors by using specific models and makes of cars. My latest model is VW Bug Cyber Green and BMW Flare Red.

I use 3M blue vinyl masking tape for sharp edges. I use regular masking tape for all others. I recommend 3M/Scotch-brand masking tape only. I also use a 3M paper/mask dispenser that I bought at the Sherwin Williams home painting store. Please, do yourself a favor and drop all the newspaper and tinfoil masking and go the system used by every serious car painter in the world. I recommend that every human being on the planet purchase a tape/paper dispenser. There simply is no substitute. The paper rolls (I use the 9â€ paper rolls myself) can be found at home Depot or Lowes’ and are definitely worth the $1.50 per roll price. I told everybody about the 4 Â½ hour paint job Doug Moon and I did on my 2002 Nats plane the Shear Panic. I believe the paper/mask dispenser was one of the factors that made that kind of speed possible.

The clear I am currently using is the Matrix MS-42 2 to 1 premium urethane clear, with the MH006 hardener, or the MH008 hardener in hot weather. All of the major paint companies offer a premium 2 to 1 clear. You could substitute PPG or Dupont, and in particular PPG’s bargain line of paints called Omni has a very nice 2 to 1 clear that is very suitable to our application. I have also used 4 to 1 clears, including Chromaclear and Valspar and they behave exactly the same as each other. I like the 2 to 1 clears better. When I first started using the clears myself, Bill Wilson happened to give me the Matrix clear, as it was a sample from a sales rep. I would have normally been using Valspar brand, because that is what Bill uses, but I took home the Matrix clear and that is what I have been using ever since. In fact, I have grown to really love the Matrix clear, as it performs wonderfully and is priced very reasonably, at nearly half the cost of Chromaclear.

I thin (or reduce) the clear coat from 33% (2-1-1) to 100% (2-1-3) depending on what I am planning to shoot. I typically shoot at close to 100% reduction or slightly less. I use Omni medium, slow, or super-slow urethane reducer depending on the temperature. I use the Omni reducer because I have found that it is IDENTICAL to the PPG urethane reducer that I was using before, and the Omni costs about one-fourth as much (it is also what my local shop carries). A gallon of Omni reducer costs less than $20 and can be used in the primer also. Feel free to use whatever brand urethane reducer you want, as I am sure they are extremely similar.

The real function of the reducer in the clear is to give the modeler a chance at a light clear coat. We are painting model airplanes after all not cars, so a thick heavy coat of clear, (while desirable) is not practical. Urethane auto clears are high solid. High solids content simply refers to the fact that there is actually more material in the can and less solvents (epoxy, for example would be considered 100% solids-as it loses no weight as it cures). This has been the trend in auto paints for years, resulting from enormous pressure from the EPA. Dope clear for example, is typically a 10% solids and 90% evaporating solvents, so it would take 6 times as much dope clear to equal a 60% solids auto clear (it also takes much more time to gas off). The urethane reducer used in the clear serves to stretch the material into a thinner coat, resulting in a reasonable weight. The reducer can also serve help the clear flow and flash a little slower if the hardener is a little fast, as most spot repair hardeners often are. The slower the clear dries the more it will lay out typically, but it will also serve to allow more trash to stick to the wet surface, especially if you are painting in your garage. Everything is really a compromise in the end.

I have been doing pretty well with using one slower reducer when thinning the clear if a slow hardener is not available. So, for example, if the temperature calls for medium reducer (70 deg.-80 deg.) I use the slow (80 deg. -90 deg.). Don’t get cute and think that using a super slow reducer when it is 60 degrees will result in a finish that looks like a mirror. Most likely you only succeed in trapping the solvents in the first coat and popping the surface with the second, which will result in a bunch of tiny little air bubbles to appear in the surface.

3 oz of clear, 3 oz of reducer for a total of 6 oz in the gun will do a Nobler sized plane if the overspray is kept to a minimum. The result will typically be a 1.5 oz clear coat (see note). The first coat is shot semi-gloss, the second is shot a little wetter. Allow 10-15 minutes in between to let the reducer gas off out of the previous coat. Don’t try to fix all the orange peel until you give the material 10 minutes to flow, you might be surprised how much it will. The 2 to 1 clear is just so much easier to shoot and seems to not want to run if "stacked" like the 4 to 1 clears. Not to mention the shine is at least triple.

Note: If a clear is a 2 to 1 mixture it is typically 60% solids (thank the EPA). Using a gravity fed "HVLP compliant" Harbor Freight gun, which averages about 75% of transfer, 75% of 60% of the weight of the clear (actual clear, not reducer) will end up on the airplane. Using rough numbers, 50% of the clear in the gun will end up on the plane. I found that this does definitely work in practice. When shooting my profile P-Force I used the 6 oz mixture and 50% of 3 oz ended up on the airplane, so the clear weighed about 1.5 oz. The mistake I made in the past was not thinning the clear enough to allow the material to flow out nicely (or cover the area). This is not a car, after all, and 50% of what is needed on a car is still quite a lot of clear. When I first started using the auto clears (read that did not have a clue) I typically used a lot of material to try to get the material to "lay out". I shot 12 oz of unthinned clear on my Oriental. I wish I could go back and do that again. My guess is that clear job weighed about 5-6 oz. People who are used to shooting dope, which is closer to 10% solids will typically shoot WAY TOO much of a high solids clear. Using logic, one coat of a premium 2 to 1 clear is equal to 6 coats of dope at FULL STRENGTH. Which, by my numbers, equates very nicely to about what the dope guys end up shooting on a plane (10 to 15 coats-Windy uses a quart on a plane). The difference being that two coats of thinned urethane clear will lay flat and will only need rubbing if you are a true aficionado. Most guys would be sufficiently impressed with "OEM" car shine.

All of the urethane auto clears are extremely fuel proof. I typically run as high as 30% nitro in my 4 cycle engines. Even with these high nitro fuels, if spilled directly on the finish, have no effect. I regularly clean my airplanes with alcohol, and I have even used lacquer thinner for spot cleaning. Needless to say, an airplane with urethane auto clear will keep its gloss for years and years, long after a dope job has faded and dulled.

Sanding and buffing auto clear is really no different than sanding and buffing dope clear, except for the fact that the auto clear will already be glossy when you start and the buffing compounds may be slightly different. The beauty of the gloss clear is that it is not necessary to buff every square inch of the airplane, which is typical in a dope clear job, because the material is already shiny. It is amazing how little sanding and buffing required to have people convinced that you sanded and buffed the entire plane. I always sand and buff the top and bottom of the wing, but I don’t necessarily buff the flaps. The top of the fuselage definitely takes priority over the bottom, etc. I try to get my clear to lay out flat enough that sanding and buffing is simply something to do if I get bored, but very few people notice a huge difference.

The clear is wet sanded in the usual manner, starting with wet 3M 1000 grit Wet or Dry (this is the only time that wet sanding is appropriate in this method), commencing to 1500 and then even 2000 if you wish (not really necessary). Once the surface is flat, machine or hand-rub using 3M Rubbing Compound. You will find that the 3M Rubbing Compound will do the bulk of the smoothing and shining work and the surface will be almost back to the original level of shine when completed. Progress to 3M Micro-Finishing Compound (this material is best used with a machine) and the surface should be back to the original level of shine. For appearance judging a quick rubbing with 3M Finesse-It will really wow them.

EQUIPMENT:

After the Polycrylic stages, this paint method is primarily a spray method, so there are some equipment requirements. Bill Wilson has spent a great deal of time testing inexpensive equipment solutions for spraying. Spray guns have been of particular concern. The gun I use for primer, basecoat, and clear is the Harbor Freight HVLP "compliant" gravity feed.

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=43430

This is the gun that started the gravity feed revolution for the Texas stunt community. Bill Wilson was using one of the several variations at his body shop and after Steve and Doug Moon and I used it, we had to have one. I bought one, the Moons bought theirs, and I got one for Al Rabe, which he gave to Frank McMillan, and so on, and so on...

This gun, as well as all gravity feed type guns, is capable of shooting paint at very low pressures (around 10 to 5 psi depending on the viscosity of the material). Since it does not rely on the air pressure to feed the paint to the nozzle, overspray is truly minimized. The transfer rate of the gun is approximately 75%. Not to mention the fact that the cleaning of the gun is truly light years ahead of the cleaning process required for a suction feed gun.

I recently added a "clear only" full sized gun and a Harbor Freight detail gravity feed gun for painting trim colors. The trim gun works very well for the task of shooting masked areas as it naturally shoots very "dry", which is perfect for basecoat. It was on sale for $34.95 with the regulator and I just could not turn it down.

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=46719

This little guy is great for dry coats of small trim, or simply freehanding a camouflage job on your semi-scale. It is capable if a fan varying from 1/8" to about 3", and could be used as a main gun, but it would be SLOW GOING. I would recommend buying the big gun first.

I would also recommend a filter unit for your air supply to eliminate the oils and water vapor that can end up in your paint. They can be had real cheap at Harbor Freight, though (under $30).

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=42035

I would recommend putting the filter unit as close to the gun as possible. I actually mount mine right after the compressor unit and make sure to keep my hose short enough that there is not a lot of condensation in the feed line. If you choose to not use a full size regulator/filter unit I would suggest a disposable filter/water trap that can be attached to the base of the gun. These can be found at your local auto body store.

I have had several people ask me about buying a compressor unit, as it seems to always be the first step to becoming a full time spray painter. I have a Cambell-Hausfeld 3 hp/110 V single stage with a 20-gallon tank that I bought Wal-Mart more than a several years ago. This compressor is really more than enough for any painting operation I have ever done, and is adequate for most body shop and mechanic's air tools. It is really not necessary to go quite this big for painting alone. Harbor Freight has a good 2 hp pretty cheap (under $110).

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=40400

Safety:

There are a lot of discussions about the potential safety hazards surrounding the catalyzed urethane paints, especially the auto clear coats. Years ago, when the Imron series of paints from Dupont were popular (a particularly hazardous paint system), there were several horror stories going around the control line stunt community. In following with these stories there were a lot of half-truths and misconceptions bantered about. Hopefully, some of that will be clarified here.

The first misconception is that any painting system is safe. There are simply no solvent-based painting systems that do not require proper protections. Without the proper breathing apparatus and protection from skin exposure all of the paints and glues used in modeling are unsafe to a certain degree (excepting the maybe aliphatic glues and their cousins). Dope systems are certainly not immune to safety concerns, as well as epoxies, enamels, and cyanocrates.

One of the main factors in evaluating whether a system is safe or unsafe is exposure time. This is one the most overlooked factors when comparing the hazard in each system. There are certainly addition chemical hazards when dealing with the clear stage of the auto paint systems, but the exposure times are so much drastically smaller in comparison to say, a dope system, that the case could be made that, in the end, the auto system is actually more safe. For example, for say a .60 sized stunt ship, a dope clear job would typically consist of one to two quarts of reduced material. This would typically require anywhere from 5 to 10 sprayed coats. If each coat requires 20 minutes of spraying time, the total exposure would be roughly from 2 to 4 hours. In comparison, for a .60 sized stunt ship, I typically spend about 10 minutes spraying the tack coat of auto clear and probably 10-15 minutes on the second wet coat (there is a lot more watching and looking on the final coat). Typically I only fill the spray gun with 6 to 18 oz of reduced material (depending the size of the airplane and the high zootness of the paint job). Due to this fact, it is easy to see that the total amount of atomized paint floating around in the air is drastically less with the auto clear.

As far as the safety of the total system outlined in this article, the exposure to any hazardous chemicals has been minimized. There is minimal exposure during the Polycrylic stages. I seldom feel the need to wear a mask and my wife never complains of the stink in the house, so the largest portion of the finishing process is spent with no stink at all. The primer stages are relatively quick, as only two coats are required, one rough and one final, and both of these could be accomplished in the same day if one is diligent. The basecoat colors are really quite benign, and have a smell similar to Red Devil Enamel. Since they gas off so quickly and use such mild solvents, skin exposure risks are also relatively mild. The clear is the most obvious health hazard, but the exposure is so short I feel the tradeoff is well worth it.

I just so happened to buy a new organic vapor mask, (a 3M silicone half faced model) so I took the opportunity to call the 3M Technical Service Line to get the 411 on the effectiveness of organic vapor carbon mask on diisocynates. Diisocyanates are the most hazardous chemicals present in the auto clears. Much to my surprise, despite what we have been told in the past, carbon based filter cartridges are completely affective against these chemicals, even more so than most solvents. The use of fresh air systems is not even advocated by OSHA under normal conditions. The only reason fresh air systems were EVER advocated for diisocynates was because there were no warning signs for these chemicals (like a smell). You can read the whole article here.

http://www.3m.com/occsafety/pdfs/respirator1.pdf

This is the nuts and bolts of the article.

Misconception No. 1: Air-purifying respirators should not be used because diisocyanates have poor warning properties.

Although OSHA specifically permits change schedules in lieu of sensory warning properties, some health and safety professionals argue this is not a safe practice. They believe diisocyanates could enter a facepiece through a spent cartridge or defect (e.g., a torn exhalation valve), and the user would be unaware, risking prolonged exposure.

Misconception No. 2: Air-purifying respirators cannot remove diisocyanates.

In fact, it has been known for many years that diisocyanates are adsorbed by activated carbon and retained extremely well. Cartridge breakthrough equations predict very long service lives for diisocyanates under plausible use conditions.

Misconception No. 3: Air-purifying respirators are not approved for gases and vapors with poor warning properties. NIOSH supports OSHA’s requirement for change schedules and recommends against relying on warning properties. In addition, NIOSH recently directed respirator manufacturers to change the cautionary language on cartridge and canister approval labels and user instructions to be consistent with 1910.134. Specifically, the statement do not wear for protection against organic vapors with poor warning properties or those which generate high heats of reaction with sorbent must be changed to follow established cartridge and canister change schedules or observe ESLI to ensure that cartridges and canisters are replaced before breakthrough occurs.

Besides the inhaled vapors of any solvent or diisocyanate, there is also the risk of exposure to the skin. I personally take this very seriously, since the only adverse reaction I have had to the auto paints actually came from DIRECT LONG TERM EXPOSURE TO THE SKIN. I simply don’t recommend it. My latest method for avoiding skin exposure is wearing treated paper (Tyvek) hooded coveralls over my street clothes when I shoot the clear. I use the coveralls a few times and throw them in the trash. Then again I am lucky that I have a convenient supply in that my boss lets me have one every now and then. They are really inexpensive (there are several sources on the Internet and the price is about $50 a dozen) but still this may not be a good solution for everyone. Another alternative would be to go to the surplus store and get a set of Air Force mechanic’s light coveralls. This is what I did when I was in college. The coveralls lasted for years and cost me about $10. I still recommend showering after shooting an entire plane in clear; it just never hurts to be safe.

The City Smasher