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Paint models with latex

Model Airplane News, Nov 2003 by Vaillancourt, Roy

More information on this great technique

Not only is latex paint non-toxic, easy to clean up and environmentally friendly, but a paint-supply store can also exactly match it to a color chip or other scale documentation. I first detailed how to paint with latex in the April 2001 issue of Model Airplane News, and since then, many modelers have written to ask me questions or to report their success. It seems that many of you still have questions about this process, and even those folks who have had pleasing results have followup questions. In this article, I answer some common questions and share a few tricks and tips that I learned since I wrote the last one. Editor's note: to see Roy's original how-to article, take the Click Trip at modelairplanenews.com.

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Q CAN YOU USE LATEX PAINT ON A NITRATE OR BUTYRATE DOPE WITHOUT A PRIMER?

A Yes, but the key is to make sure that the dope is fully cured. Most dopes release gas for a fairly long time-sometimes for three to five weeks, depending on the temperature and humidity. To test it, sniff the surface; if you can still smell the dope, it isn't fully cured. If you paint over the dope before it is cured, you trap the gas, and it will eventually dissolve the latex or lift it. (This also happens if you put epoxy, primer, or other paint over dope before it's fully cured.)

In most cases, you don't need to use a primer over the dope. If you want to use a primer, solvent- and water-based ones will work. If you use a solvent-based primer, confirm that it is fully cured before you apply the latex. In any case, give the latex something to adhere to: sand the surface with 280- to 300-grit sandpaper.

Q WHAT ABOUT UNPRIMED FIBERGLASS OR PLASTIC PARTS?

A You can put latex directly on raw fiberglass, but first fill all of those little dents, pinholes and such. The best method is to sand the fiberglass first and then shoot two coats of primer over it. Next, sand the primer almost off to leave a faint gray area to show you where your plane needs a little more work. Fix these areas, and apply just enough primer to cover the repair. Sand the area again lightly. Try to maintain a light shade of gray. When I sand off all the primer before I apply the latex to the raw fiberglass, I get a great finish without the added weight of the primer. You can also apply latex directly to unprimed plastic parts and be sure of great results. Whether you paint fiberglass or plastic, the key is to make sure that the surface has enough "bite" for the latex to bond; 280- to 320-grit sandpaper works best. Don't make the parts too smooth, or the paint won't stick well to the surface.

Q WHAT ABOUT UNPRIMED FABRIC AND PLASTIC FILM?

A I have painted fabric-covered aircraft and those with only fabric-covered control surfaces without priming the fabric. I applied the latex to "raw" Super Coverite. The latex took to the Coverite as if it had been made especially for it-great! When the fabric sags or becomes "dented," you can apply heat to reshrink it, and the paint just goes along for the trip. This technique can also be used on any iron-on fabric covering. I also discovered that latex paints don't crack because of vibration or when parts shrink or expand. Remember, latex is rubber!

You can also paint over plastic film, but you need to roughen it first. Remember: latex needs to bond mechanically with the surface. Steel wool will work well to roughen plastic film. The finer-steel wool "grits" are graded in an "aught" scale: 0, 00, 000, 0000. The more 0s, the finer the steel wool. For most plastic films, "triple aught" (000) or "four aught" (0000) works best. You should always test a piece of scrap material first; if the latex paint you apply peels off, you need to use a coarser steel wool.

Q WHICH KIND OF PRIMER IS BEST?

A When I use a primer, I usually choose automotive lacquer (solvent-based); I only recently tried others. Some water-based primers work very well and "sand" just like the lacquer, but I've found that they take longer to dry than solvent-based primers; both work well to fill those little nicks and dings. I prefer to use a light gray or white primer because the colors show the surface imperfections a bit better than other colors after filling and resanding, and they provide a better base for any subsequent top color.

Q CAN I USE A HIGH-VOLUME, LOW-PRESSURE (HVLP) SPRAY GUN?

A You should be able to use any HVLP guns on the market today. You'll need to play with the air pressure and the quantity of thinner you use. Don't be afraid to experiment; latex paint varies with the manufacturer. You will also find that using a different color can require you to change your settings and technique. just go easy, and change only one setting at a time.

Q MUST I CLEARCOAT LATEX TO FUELPROOF IT?

A This depends on the kind of fuel you use. If you use a gas engine, you don't need to clearcoat the latex. It withstands exposure to gasoline very well after it has cured. If you use a glow engine, however, you will need to clearcoat; latex turns into a gooey mess when glow fuel gets on it.

Paint models with latex

Model Airplane News, Nov 2003 by Vaillancourt, Roy

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