It happens every spring. The air warms, the birds sing, the trees bud, the flowers bloom, and people look around at all this natural beauty and say to themselves, “Man, does that fence need painting.”
Yes, there’s something about the spring and summer that brings out the handyman–er, handyperson–in all of us. And topping the list of things to do is often painting. But purchasing the perfect paint is a perilous pursuit, because paint is a complex substance.
It hasn’t always been. The first paint was basically rust in water, used for cave paintings 17,000 years ago. The ancient Asians, Egyptians, Greeks, Romans and Incans had a few more pigments, and began mixing them with gum arabic, egg white, gelatin and beeswax to form a variety of paints.
The Chinese discovered that paint could be protective as well as decorative by about the second century B.C., when they started painting wooden buildings with lacquer; the Europeans didn’t catch on until around the 12th century A.D. The first commercially prepared paints didn’t appear until the 19th century.
Modern paint consists of three different types of materials: pigment, vehicle (sometimes called binder) and carrier. The pigment is what gives the paint its color. It’s a fine powder that either scatters all wavelengths of light in all directions (white paint), absorbs them all (black paint), or absorbs certain wavelengths and reflects others (colored paint). Iron oxide, the choice of cavemen everywhere, is still used to make red, yellow and brown paints. It has the advantage of being cheap, which is one reason you see so many red barns.
The vehicle holds the pigment and adheres to the surface being painted, creating a skin-like coating of uniform color. Vehicles are usually either resins such as acrylic, alkyd, polyurethane, vinyl or epoxy, or oils such as linseed, soybean or tung. Vehicles undergo a process called “curing,” which can take from several hours to several days, depending on the paint and the environmental conditions, during which they react with oxygen in the air to become tough and insoluble.
Curing isn’t quite the same as “drying.” Paint doesn’t stay “wet” very long, but it stays “tacky” for hours. (Actually, on some houses whose owners have an unfortunate sense of aesthetics, the paint job stays tacky for as long as they own the place.) The “wet” part of paint, which is what makes it flow easily and evenly onto a surface, is the carrier. That carrier is usually either a solvent or water.
In solvent-based paints, better known as “oil paints,” the vehicle is usually dissolved in a thinner, such as turpentine. This solvent evaporates rapidly once the paint is thinly spread on a surface, leaving behind the vehicle and the pigment. Solvent-based paints were once the most common, but that’s changed dramatically in the past few years as studies have shown that a very large component of air pollution in cities comes from drying solvent-based paints.
Instead, painters increasingly are turning to “latex,” or water-based paints, which first became available in 1949. In a latex paint, the carrier is water. The resins used as vehicles for the pigment don’t dissolve in it: they’re suspended in tiny micro-droplets. As the water evaporates, these droplets bind with one another to create the layer of paint.
In general, paints intended for outdoor use are more expensive than paints intended for indoor use. That’s because outdoor paints takes a beating from sun, wind, rain, snow, hail, pollution, insects and a host of other environmental factors, so paint manufacturers put the highest-quality resins and pigments in them.
Interior paints don’t have to be quite as tough, so they can be made from lower-cost resins and pigments. Another difference is that exterior paints are frequently quite glossy, while most people prefer a flat, non-glossy look to their interior walls. The difference between a flat and glossy look is in the amount of resin. Generally, the more resin, the more gloss, because a high-resin paint dries very smoothly, while one with less resin dries more roughly. That rough surface doesn’t reflect light as well, and so doesn’t shine like a glossy surface does.
So now, armed with all this new knowledge about paint, you should be better prepared to go forth this spring and refurbish your fence, your deck, your garage, your trim, even the entire house.
And me? Well, I’ll be sitting there in the sun in my yard, egging you on.
