paint selection lab testing

Paint Selection: What You Should Be Considering and Why

 “What kind of paint should I get?” There is no one answer to this question because there are many different situations that would need to be considered, along with personal preferences.  Anyone who has ever walked into a paint store or paint department of a home improvement store can easily become overwhelmed by the sheer number of options.  But if you understand what all those options are, your decision will become easier.  This article explores some of the decisions you will need to make when selecting the type of paint to use, including interior versus exterior exposure, gloss level, color, the need for a primer, and oil (solvent borne) versus latex (waterborne) formulations.

Interior versus Exterior

One of the easiest but arguably the most important factors in selecting a paint is whether it will be used to protect interior or exterior surfaces, since those represent very different environments. Paints formulated for exterior use will contain raw materials designed to combat what mother nature produces year after year, such as sunlight, rain, ice and snow, and temperature fluctuations. Interior paint formulations do not have the same raw materials as exterior paints. They may look and apply the same, but they are very different and perform differently once in service. Exterior formulations will work on the interior, but not vice-versa, so the first question that needs to be answered is “Interior or Exterior?”

Gloss

The second attribute to consider is the gloss, or sheen level (the terms “gloss” and “sheen” are used interchangeably).  Gloss is indicated by how much a paint surface scatters light that hits it.  Low gloss paints scatter light very well, which gives them a dull or flat appearance.  High gloss paints reflect more light (instead of scattering it) and can appear shiny depending on the amount of available light. Common gloss levels include:

  • Flat (or matte)
  • Eggshell
  • Satin
  • Semi-gloss
  • Gloss

Not every brand and product is available in all six gloss levels and some paint manufacturers use different terminology.  It is important to recognize that there is no industry standard that establishes minimum/maximum gloss values for each of the levels.  For example, each company may have different gloss level ranges for “eggshell” so two different brands of an eggshell finish paint may look different after they dry.  To minimize variations, choose a manufacturer, product, and gloss level and stay with that product as much as possible, especially if you are painting different surfaces in the same space.

Higher gloss paints tend to be “shiny” and can cause glare.  They also exaggerate any imperfections on the wall surface, so they are frequently avoided in spaces like family rooms or living rooms.  However, gloss finishes tend to be more durable and easier to clean, which makes them ideal for rooms that experience a lot of moisture or stains like a bathroom or a kitchen.  In addition to being more durable, glossy finishes draw the eye, which makes them a good choice for trim, door frames, cabinets, or other similar features in a space. “Flat” finishes however are at the other end of the spectrum.  These paints tend to be best for bedrooms and other low-traffic rooms, as well as ceilings.  Low gloss paints will “hide” many imperfections like bumps, dents, and cracks.  Although they may be more visually appealing than gloss finishes, they are frequently softer and rougher than higher gloss paints (due to pigment load and fineness of grind), so they are less durable and harder to clean.

Fortunately, there are more than just two choices when it comes to gloss level.  The intermediate levels (eggshell, satin, and semi-gloss) allow you to customize the finish you desire.  Eggshell and satin finishes are very popular because they look good in many situations and have good durability.  The bottom line is that the selection of gloss level is a personal preference. Parents with young children, for example, may consider using higher gloss paints in certain areas that need to stand up to more abuse.  Or a homeowner with older walls that show some wear or minor damage may opt for a less glossy paint to help hide imperfections.  Most retail paint stores/departments have examples of the various gloss levels to help you decide what is right for your project, but keep in mind that color selection can also have a visual effect on perceived gloss; that is, darker colors will frequently appear more glossy than pastel colors of the same gloss level. Gloss measurement and retention is described in a 2017 KTA University article, “Measuring Gloss Retention in the Coatings Industry.”

Color

Preferences vary considerably when it comes to what color to use.  And every major paint manufacturer has literally hundreds of colors and shades to choose from.  Simply choosing a color at the store and assuming it will look the same in the space or surface you intend to paint can lead to disappointment and even repainting. Color selection goes well beyond preference.  Many colors will look different in different light. For example, fluorescent lights, soft or clear incandescent bulbs, LED lightbulbs and light/lamp shades will all create a different color appearance in interior spaces. Even natural sunlight can look different depending on the degree of cloud cover or the time of day.  Matching existing colors can also be challenging. It is possible to have two objects that appear to be the same color in one type of light look different under another type of light.  Gloss level (described earlier) can also affect how a color appears.  High gloss finishes frequently make a color look slightly darker, while flat finishes can make a color appear slightly lighter. To reduce the risk of disappointment after application, test the color in different places in the actual space/on the surface you plan to paint.  If using paint color swatches, tape several to vertical locations or move them around often and look at them at different times of day, especially when there is natural light coming into the space through windows.  Some retailers will tint small samples of the paint that will cover an area larger that a color swatch will, to get a more realistic indication of what it will look like.

Finally, when selecting a color, it is important to consider what you will be painting over.  If the surface is already painted an even coat of new paint is important, but you will also need to completely cover the color of the existing paint so it doesn’t show through.  Most applications will require at least two coats to hide what lies beneath, despite claims of “one-coat coverage.”  Paint technology is constantly advancing, and more and more manufacturers are formulating paints that claim to cover with just one coat.  These paints do have substantially better coverage capability but are often more expensive. Darker, deeper colors are notoriously difficult to cover and may require three coats, whereas lighter colors require fewer coats to achieve hiding.  The same is true for new paint too.  Light colored paint has more white pigment in it, so it is better at hiding the colors beneath it.  When painting over a color that might be difficult to hide, consider using a primer first, which leads us into our next topic: Primers.

Primers

Associated with the question of which paint to use is whether a primer is needed. Applying a primer may seem to some like a lot of extra time, effort, and money for essentially no aesthetic benefit, and sometimes primers are not needed. However, in many cases a single coat of primer can save time and money with fewer coats of the more expensive finish coats.  It is beneficial to understand what a primer does in determining if one is necessary.  Primer is essentially paint that is intended to be covered by another layer of paint, so primers are flat (no gloss), highly pigmented, and often white. They are designed specifically to do a few things well. 

A good primer will adhere to clean surfaces and provide a good foundation for the finish coat(s).  If the existing paint has defects but is well adhered, a primer will help to hide some of those defects.  Very rough or porous surfaces (for example, new unpainted drywall, wood, or masonry) require more paint to cover because the paint will penetrate or soak into the softer substrates or will need to fill the imperfections to provide a sealed/smoother surface for the topcoats.  Many paints have difficulty adhering to smooth, glossy surfaces.  A primer can be useful in this situation too because it is designed to adhere well and provide a fresh surface for the topcoat to “grip” onto. Glossy surfaces should be sanded before applying a primer or finish coat. Note that older paints may contain lead so proper personal protective equipment should be worn when sanding. LeadCheck swabs are available from various retailers to determine the presence of lead in paint.

Primers also help with hiding.  As described earlier, certain existing colors can be difficult to hide.  Primers are typically less expensive than finish coats so one primer coat and one finish coat can be less expensive than two finish coats.  Some primers provide “stain blocking,” which means they are specifically designed to prevent existing stains from bleeding through the newly applied paint.

A primer may not be necessary if none of these conditions are present.  That is, if the existing paint color is neutral you can often hide it without a primer.  If the new color is similar to the old color, it will be easier to hide.  If you have a clean, nonporous surface that isn’t too glossy, the adhesion of the finish coat may be fine without a primer. Or if there is localized staining or damaged spots, consider priming only those areas (i.e., spot prime) instead of the entire surface.  Note that some brands will promote “paint and primer in one” or “self-priming.”  This does not mean there is primer in the paint, but rather they contain greater amounts of good quality hiding pigments and are thicker in their consistency (known as viscosity).  They are more expensive but may save considerable labor costs. 

Oil-Based or Water-Based

Paint is made up of resins, pigments, and additives suspended in a carrier or solvent.  The solvent evaporates as the paint dries, leaving behind the resin, pigment, and additives.  The carrier or solvent can be water, or one or more organic solvents. Acrylic latex paints often use water and coalescing solvents, while oil-based paints (also known as alkyds) often use a hydrocarbon solvent such as mineral spirits to reduce the viscosity of the paint and assist with flow-out/leveling.

In the past almost all paint was oil-based. The combination of linseed oil, lead, and mineral spirits created an outstanding paint that protected a variety of surfaces for decades. Now water-based latex technology is dominant for both interior and exterior applications.  Aside from the elimination of lead from consumer paint formulations, the primary reason for moving from oil to waterborne formulations is the need to reduce ozone-producing chemicals in the atmosphere. When most hydrocarbon solvents evaporate into the air, they photochemically react with sunlight and produce air pollutants that can affect public health. These are called volatile organic compounds, or VOCs.  Water-based paint technology does not produce these air pollutants.  As countries around the world impose stricter air quality regulations, water-based coatings (both architectural and industrial/marine) will become more commonplace.

Oil-based paints do have a few advantages over waterborne technology.  When dry, they form a very hard, durable, water-resistant surface and can also have a very glossy finish.  They are best for surfaces subject to mechanical or abrasion damage, like doors and trim.  They can also be useful in high moisture producing spaces like bathrooms.  Some claim oil-based paint is easier to apply because it goes on smoothly and evenly and levels better than water-based paint, reducing brush marks.  They can also be applied at colder temperatures than water-based paint. It is not recommended to apply water-based paint when the temperature is below 50°F or is expected to fall below 50°F before the coalescence (drying) process is complete.

The solvents in oil-based paint can be hazardous and should only be used in well-ventilated areas.  These paints require solvent like mineral spirits for clean-up (soap and water will not work) and these petroleum-based solvents are flammable.  Although very durable, oil-based paint will deteriorate over time and become brittle, then crack or peel since the oxidation process used to cure the resin doesn’t stop until the paint is fully oxidized, which occurs over many years.  Like most paints their color fades, and they will chalk when exposed to UV radiation from the sun.

Water-based paints have many advantages over oil-based paints. They have little to no adverse impact on humans or the environment.  They are easier to clean off brushes and other tools after application, (usually requiring only soapy water) and they are readily available (unlike oil-based paints, which are becoming more difficult to source from consumer retailers). Provided they are not applied when it is excessively humid or cold, latex paints dry much faster than oil-based paints.  While they generally aren’t as durable as oil-based paint, water-based paints have greater resistance to sunlight (when formulated for exterior use). Waterborne technology is not restricted to residential/commercial use. Caltrans has been using water-based paint technology on their highway bridges for several years, and many southern state transportation agencies like NC DOT started using waterborne finish coats years ago.  

“What kind of paint should I get?” As you now know, there is no one answer to this question because there are so many considerations, including personal preferences.  Decisions always become easier when you understand your options versus just knowing what they are.  This article explored some of the decisions you may need to make when selecting the type of paint to use.

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