Paint models with latex

An inexpensive, safe finishing alternative

Environmental concerns increase daily, and we now know that many materials we use are not environmentally friendly. Many solvent-based paints are high on the list. As the EPA and other agencies have removed these substances from the store shelves, we must find suitable alternatives. Latex paint is non-toxic, allows your spray equipment to be cleaned up with ordinary soap and water rather than harsh chemicals and is much better for the environment than solvent-based paint.

I began to use latex to finish my airplanes in 1983. After a mishap with my P-47 Thunderbolt, I needed to repair and repaint it. At the time, I was using K&B SuperPoxy paint, but when my Benjamin Moore paint dealer told me he could match all my scale colors perfectly-for about an eighth of the cost-I had to give it a try!

After making the repairs, I did all the usual panel lines and rivet detail as before, and I repainted my Thunderbolt in the same scheme. I applied the latex over conventional automotive primer. Most surprising was that the plane lost weight after the process. In all, my 92-inch-span Jug weighed 41/2 pounds less than before. Whoever heard of a model losing weight during a repair?

When you use it, latex feels thick and heavy compared with other paints; actually, it produces a lighter finish once it has dried, and it generates very little overspray. Latex doesn't like to be wet-sanded; it will begin to roll up if it gets wet for too long. I found that, with some practice, I could sand a latex finish successfully to a fine, feathered edge. Latex can also be applied directly to unprimed, fabric-covered areas. I use SuperShrink Coverite; latex sticks to it as though it was made especially for it. The nice thing is that even if the fabric sags or gets dinged, you can simply reapply heat and shrink the fabric tight again without affecting the paint. Since it's a rubber-based paint, latex does not crack because of vibration or the expansion and shrinkage of parts.

We have all been taught that you're supposed to apply light colors first, followed by darker ones, but with latex, this is not necessary. When I painted my fabric-covered, Stinson L-5, I first painted the whole model Olive Drab (OD), then added the light gray underside colors over it. I did this so the inner surfaces of the cockpit would match the outside color, and the OD latex showed through the fabric very nicely. The plane required three coats to cover, and the light gray required two coats to cover the OD areas. Talk about breaking all the rules! Latex also holds up very well when it's applied to fabric; after 10 years of flying, the plane looks as good as the day it first left the shop.

I have also used latex over unprimed, fiberglassed surfaces with good success. For my L-19 Bird Dog, I sanded all the primer off except where panel lines and hatches were. I scuff sanded the glassed surfaces with 280- and 320-grit sandpaper, and the paint stuck as if it were welded on! Epoxy paints used for aircraft markings can be applied over a latex finish if you don't flood the epoxy paint on. If you saturate latex with anything containing acetone or toluene solvents, it will turn it into a rubber-cement-like goo.

APPLYING LATEX

When it's time to paint, be ready to play with the air pressure. For either a touch-up gun or an airbrush, I start with about 20psi of air pressure, although this can vary by 5psi depending on the brand of paint and how much pigment it contains, the amount of thinner added and even the color being used.

I start by adding about 20 percent thinner to just a bit of paint; then I test-spray it onto a piece of glass. If it doesn't flow properly, I increase the air pressure a bit. If it still doesn't flow through the gun, I put the air pressure back to where it was and add thinner. If the paint "spits," I add more thinner. If it comes out wet and runny, I add some more paint. The idea here is to use a small jar of paint to find the correct mix ratio for that color. Adjust your gun for low paint flow. If you get runny stuff even at low-flow settings, then you have added too much thinner. If it comes out dry-looking, increase the flow of paint or add thinner. Very rarely will you use less than l5psi of air pressure. Do not spray paint with more than 30psi air pressure; this will cause too much overspray.

When you use latex, the weather doesn't matter. I usually paint in my basement shop in the winter; the temperature there is usually about 55 degrees (I like it cool). I have sprayed latex on rainy, cold and damp days, and results are the same as on sunny July days. In fact, latex seems to be easier to work with on cold, damp days. I just keep a heat gun around to accelerate the drying time between coats.

On cold days, I spray the first coat on just heavily enough to barely see some coverage. I then dry it with the heat gun and spray the second coat on just a bit wetter. After drying that coat, I spray the third coat then go upstairs and let the paint dry overnight. The next day, I go over everything with the heat gun once more just to make sure it's completely dry.