Interior Paint, Exterior Paint, Architectural Paints
Your customers invest in an interior or exterior paint job to either protect the surfaces to which the paint is applied or make them more attractive, or both.
by John G. Stauffer
job to either protect the surfaces to which the paint is applied or make them more attractive, or both.
Regardless of the objective, painting is successfully achieved only to the extent that the coating remains bonded to its substrate and retains its essential properties. Ensuring that it does requires careful selection of the paint as well as close attention to surface preparation and skilled application.
As a painting contractor, your understanding of how a paint’s raw materials affect performance will help you select the right paints for your customers. And, when you stop to think about it, specifying the right paints, especially top quality paints, and explaining their benefits to your customers is smart marketing...for two reasons.
First, top quality paints will provide your customers with added protection and a paint job that will look good for years, both of which will enhance your reputation for doing quality work. And second, your ability to explain the benefits of these paints will make you an “expert” your customers can rely on.
To help you better understand what’s in a can of quality paint and the difference raw materials can make, the Paint Quality Institute provides the following information.
There are two general classifications of paints: solvent or oil-based paints, and water or latex-based paints. The names refer to one of the primary differences between the two categories of coatings; namely, the liquid or “carrier” portion of the paint. The liquid portion of oil-based paints contains solvents such as mineral spirits. In latex-based paints, it contains water.
Quality oil-based paints have good hiding properties and offer excellent adhesion. Many can be applied in temperatures below 50F. Oil-based paints are often recommended for repainting heavily chalked surfaces and surfaces with multiple layers of oil-based paint.
However, oil-based paints tend to oxidize and become brittle over time, sometimes leading to cracking problems in exterior applications, and yellowing and chipping problems in interior applications. They are more difficult to apply and clean up than latex paints, and they should not be applied directly to fresh masonry or galvanized iron.
Compared to oil-based paints, quality exterior latex paints offer better color and gloss retention and better resistance to cracking, UV degradation and mildew growth. Today’s top quality latex paints are also highly durable, especially those based on 100% acrylic binders.
Except under the most humid conditions, latex paints dry faster than oil-based paints, allowing a second coat to be applied more quickly. They also allow a room to be put back into service sooner because they don’t emit a strong solvent-based paint smell. And, storage and disposal are easier since latex paints do not exhibit the environmental and fire hazards associated with solvent-based paints.
Regardless of whether they are solvent-based or water-based, all paints are comprised of four basic components—pigments, binder, liquids and additives—each of which has its own effect on a paint’s performance.
Pigments are finely ground, natural or synthetic insoluble materials that give the paint its color and hiding power. The most common white pigment in paint today is titanium oxide.
The term “pigment” is also used to include extenders, which are materials such as clay, talc, mica and silica that add bulk and specific properties to the paint without adding significantly to its cost.
The binder is a resinous material that holds the particles of pigment together and provides integrity to the paint film. When paint is applied and dries, it is the binder that forms the film that adheres the paint to the surface. The type and amount of binder have a dramatic impact on a paint’s key properties, including durability, stain resistance, gloss and color retention, and flexibility.
Binders in solvent-based paints are either natural or synthetic. Today, more than 90% of all solvent-based paints use alkyds (chemical compounds made from vegetable oils and synthetic resins) as binders.
Binders in water-based paints are synthetic. The two most common are “acrylic” (or 100% acrylic) and “vinyl acrylic” (also called polyvinyl acetate or PVA). 100 percent acrylics provide better overall adhesion on a wider variety of substrates than vinyl acrylics.
Paints with all-acrylic binders also are more durable, especially when applied to fresh masonry surfaces. While oil-based paints and latex paints with vinyl binder systems often show early color loss and film deterioration on fresh masonry, 100 percent acrylic latex paints resist the effects of alkaline surfaces.
Liquids in paints serve several key purposes. They keep the pigments dispersed in an easy-to-apply fluid state. They also keep the binder either dispersed or dissolved, depending on the type of paint. The liquids evaporate after the paint is applied, leaving behind a dry film of pigments and binder.
In oil-based paints, the most frequently used liquid or solvent is mineral spirits. In latex paints, the main liquid is water. In addition to water, some solvents are also used in a latex paint formulation. One such solvent is called a coalescent, which temporarily softens the binder particles so they fuse, or coalesce, readily as the paint dries.
Additives are combined with primary ingredients to improve the performance of the paint. Additives range from preservatives, which keep the paint from spoiling in storage, to mildewcides, which keep mildew from growing on the surface of an exterior paint. Glycols are often added to protect latex paints from freezing in storage and to keep the paint from drying too quickly after application.
Rheology modifiers are a category of additives that are used in latex paints to improve application properties and appearance. In particular, they enhance the flow and leveling of the paint, and provide better film build to improve hiding and durability.
By varying the amounts and types of pigments, binders, liquids and additives, manufacturers can create a vast variety of paints. Thus, understanding what constitutes quality in these products is important when selecting a paint.
Three indicators of a paint’s quality are its volume of solids, pigment volume content and titanium oxide content. Most of this information should be contained on the paint’s specification sheet. If it is not, ask the manufacturer’s sales representative.
1) Volume of Solids. Top quality paints have a higher percentage of binders and pigments—known collectively as solids—and a smaller percentage of liquids than ordinary paints.
The greater the percentage of solids by volume, the thicker the paint film will be at a given spread rate. This translates into better hiding, better protection of the painted surface and better durability, all of which are aspects of a higher quality paint.
Ordinary latex paints typically contain about 25 to 30% solids by volume and 70 to 75% water, while top quality latex paints generally have 35 to 45% solids and only 55 to 65% water.
If a top quality latex paint and an ordinary latex paint are applied at equal wet thickness, the higher quality paint—because of its higher solids content—will dry to a thicker, more protective, and longer lasting film. However, if the paint is thinned before use and applied at the same rate, the solids content is reduced and the quality of the paint compromised.
2) Pigment Volume Content. Pigment volume content (PVC) is the ratio of pigment in volumetric terms to the total volume of pigment and binder solids in the paint. This ratio is expressed as a percent.
Low PVC paints (10% - 22%) have a low ratio of pigment to binder and are generally associated with a glossy paint. Conversely, higher PVC paints (45% - 75%) are loaded with pigment compared to binder which results in a flat finish. Paints with a satin finish have a PVC in the 28% - 38% range.
Because they are rich in binder, low PVC paints tend to adhere better and last longer than high PVC paints. High PVC paints tend to absorb stains (interior paints especially), and erode more quickly (exterior paints).
3) Titanium Dioxide Content. This ingredient gives white and light-colored paint its hiding power. A quality white latex paint typically contains at least 2.5 pounds of titanium dioxide per gallon of paint.
Ordinary paints contain more extenders than top quality paints. As a result, they provide less hiding ability, even though their solid content may be high. Clay is a commonly used extender in interior paints. In very low quality paints, it often can be the dominant pigment.
A fairly recent development in the paint industry is the use of opaque polymer pigments with titanium oxide in latex paints. Polymeric pigments differ from extender pigments in that they have greater hiding capability. Thus, if a paint contains polymeric pigments, the titanium dioxide content may be lower but the paint can still exhibit good hiding properties.
In addition to quality ingredients, there are a number of application characteristics that separate quality paints from ordinary paints. For example, once applied, paint should level well, meaning that brush marks or roller stipple should flow out and be unnoticeable. The paint should not flow too well or it will sag or run. A quality paint will strike the right balance between leveling and sag resistance.
Several other characteristics are desirable in a paint as well, including good hiding with few coats, minimum brush and sag marks, and uniform color, gloss and sheen. Quality paints will typically perform well in all these respects because their higher solids content delivers a thicker, more durable film.
As you can see, it doesn’t pay to sacrifice quality for price. By recommending top quality paints rather than ordinary paints, your customers will receive longer-lasting protection and a paint job that will look fresh for years to come. And, in the final analysis, you’ll reap the reward of more referrals and more repeat business from those who are glad that you made the quality choice.
John G. Stauffer is Technical Director of the Rohm and Haas Paint Quality Institute in Spring House, Pennsylvania.