Choosing Between Latex and Oil Based Paints
The paint world is divided into two broad groups: latex, or water based paints, and alkyd, or oil-based paints. (See “What’s in Paint,” below.)
Homeowners and professional painters like latex paint because it dries in just a few hours and cleanup is easy. Quick drying allows the application of two coats in one day. When the job is done, everything can be cleaned with soap and warm water. To clean up after painting with an oil based product you will need turpentine or mineral spirits.
Latex paint is environmentally friendlier than its oil based cousin. Unlike oil based paint, latex emits little or no volatile organic compounds (VOCs), which are restricted in many states. VOCs create ground level smog and can irritate the respiratory and cardiovascular systems. Compared with oil based paint, latex paint is easier on the eyes, nose, lungs, and skin. It is also much more forgiving if you need to clean up a spill.
The Pros’ Choice.
In the past, many professional painters resisted using latex paint, especially on woodwork or any area that would be subjected to a lot of cleaning and scrubbing. Oil-based paint is more durable than latex paint, and it settles as it dries, meaning that it produces a smooth finish without visible brush strokes.
However, legislation to reduce VOCs has directed paint manufacturers to put research money into latex paints. This has resulted in improved products that provide attractive long lasting finishes. Today, many professional painters use oil based paint only to prime or recoat old oil based paint.
In the event you are applying two coats of paint, you have to wait at least overnight before recoating oil based paint. This can be inconvenient, especially if you can only work on weekends. If the first coat isn’t dry on Sunday, you’ll wind up waiting a week to finish the job.
Most municipalities have strict rules regarding the disposal of leftover oil based paints and the solvents needed to clean brushes and rollers, which means you may find yourself stuck with half empty containers. You could end up paying to dispose of excess paint products the same way you would pay to dispose of toxic waste.
Where to Use Them.
Don’t apply latex paint over old oil paint, unless you carefully sand or chemically de-gloss oil based surfaces before recoating in latex. On the other hand, it is perfectly fine to use an oil based primer under latex paint. Some painters do this routinely because oil primer soaks into unpainted surfaces, while latex does not.
What’s in Paint?
There are three main ingredients in paint: binders, solvents, and pigment. Some paints contain additional additives.
When paint dries it forms a film and that film is the part of the paint that hardens and is called the binder. Binders include such things as acrylics, polyurethanes, oils, and latex. For oil-based paints, alkyd, linseed oil, and tung oil are common binders. Styrene acrylic, acrylic (a clear plastic), or vinyl acrylic (PVA) are the binders in water based paints.
Solvents are the liquids that float the solid binders into place where they can cure or dry. Solvents evaporate at room temperature, which means they are “volatile.” Because they are compounds made from carbon atoms, they are called volatile organic compounds, or VOCs. Oil-based paints use petrochemicals as solvents, whereas latex uses a water based emulsion.
The pigment determines the texture, color, and covering capabilities of the paint. You can judge the quality of the paint by the texture of the pigment. Try rubbing a small sample of the paint between your fingers. If it feels milky and silky smooth, then the pigments are ground finely and you have a good quality product. If the paint feels gritty, it contains a cheaper pigment.
Paint can have additional additives that enhance certain properties, such as flow, dry times, and thickness. Some of these products are available in small cans that you can add to the paint on your own.
Choosing a Sheen.
In addition to choosing the color and whether you want latex or oil based paint, you also need to choose the degree of sheen you want. The range runs from flat to gloss. Most sheens are available for both latex and oil-based formulations.
The degree of sheen is determined by the proportion of binder in the paint. The binder determines the degree to which the paint is absorbed into the painted surface and how much pigment is left to form a film on the surface. The more binder then the less the absorption and the glossier the paint.
Flat or Matte.
A low gloss finish hides minor flaws in the surfaces you paint. Because the paint is slightly rough flat paints do not take scrubbing as well as glossier finishes. Scrubbing flat paint tends to spread out the dirt and leaving a larger dirty spot.
Eggshell and Satin.
This is glossier than flat paint with slightly better abrasion resistance. Satin is glossier than eggshell.
Semigloss paints take scrubbing moderately well. They are available in latex or oil based.
This is the highest gloss classification. It is highest in binders and lowest in absorption. Gloss paints take scrubbing well and are easiest to clean. However, the glossier the paint the more it highlights any flaws on the surface.
Years ago, this term was synonymous with oil based paint. These days, it is a loose term that refers to the glossiness of paint. The term is reliable only in that you can be reasonably sure that a paint labeled “enamel” is a semigloss or gloss paint. One manufacturer’s enamel may be glossier than another’s.
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