Question

We are trying to determine the best criteria for selecting an exterior paint.

Asked by Daniel
Portland, OR

Thinking of using an acrylic latex paint. Exterior color is a dark color. Performance is an issue as well as cost but getting a grasp about the criteria is what we're after.

Answer

 

Good question Daniel.

Given all the different brands of paint, it’s no wonder that choosing quality paint is challenging, even for professionals.

  • Not only does each manufacturer create different lines of paint within each brand, 
  • but each application is so different it demands specialized knowledge that can only be discovered through good research and reputable paint companies. 

Where do you start?

Asking the right questions

Here are some basic rules of thumb for choosing the right paint. Below them is some technical paint jargon that will help you ask the right questions.

1) Price and quality. Manufacturers want to make it easy for you to compare so they break quality down into price groups, usually in the form of different lines. Higher priced paint usually means better quality because the ingredients cost more.

There are many types of paint (latex, acrylic, alkyd, oil-based etc), and each has its intended purpose to satisfy different types of customers, e.g. professional painters, commercial painters, specialty finish painters and DIY painters.

High quality paints are:

  • easier to apply
  • flow better during application
  • hide imperfections better
  • resist fading, pealing and flaking better
  • resist mildew and
  • provide a longer service life

The bottom line is that premium paints save you time and money….however….

2) Health and safety. Just because paint performs well and is expensive does not make it safe. Most people believe low or no VOCs equals healthy paint.

  • However, no or low VOC does NOT equate with healthy.
  • The best performing paint may contain plenty of toxic ingredients that are not regulated or are proprietary and not disclosed.

Recently, a leading paint manufacturer blew the whistle on one of its chief competitors for claiming to have zero VOC paint. While the paint was zero VOC, the pigments were not, and the combination increased the VOC level far above what was claimed. They were busted by the Better Business Burea.

Do your homework before you visit the paint store. Go online and download the Material Safety Data Sheets (MSDS) for ingredients and hazardous chemicals. Check sections 2 , 3 and 11 as it will spell out most of the important information you need to know.

3) Durability. Higher quality paints have more solids content and less liquids (diluents or solvents—see below), which results in a thicker longer lasting film.

  • Paint that is filled with inexpensive fillers doesn’t hold up to scrub tests, and the best paints (glossier the better) contain 100% resin.
  • Check section #2 of MSDS for composition of solids content by volume and weight.

4) Protection. One of the main purposes of paint is to seal the sheetrock, wood, or
masonry beneath it.

A thicker coating with more solids content locks out moisture and keeps everything dry underneath it.

  • Some high-end paints are so thick and tough they require neither priming nor a second coat. This saves time and money.
  • Less expensive paints are thinner, require more coats and wear off easier.
  • The pros usually test paint quality in between their thumb and forefinger to get a feel for how thick and smooth it is.

5) Beauty. Most paint companies offer great color options but what is critical is how long they continue looking good.

If the pigment is not of high quality, that nice paint job over time will lose its luster.

  • Inexpensive paints fade, wash off and are not consistent.
  • It’s hard to tell this from reading the side of the can, and you can’t judge it except over time. 
  • That’s why you have to check references and inspect homes painted years ago.

High quality paint will still look good outdoors after 7 years and indoors after 10 years.

6) Coverage. Painting over old paint can be challenging, especially if it: has a dark color, started to peel or crack or contains ingredients incompatible with your type of paint. 

Be sure to select paint with more prime pigments like titanium dioxide (white pigment) which hides better and lasts longer than cheaper fillers like talc, clay, calcium carbonate or silica.

  • Once again, higher concentrations of solids will help fill voids and cover far better than low grade paints.
  • This information can also be located in the MSDS.

7) Cleanability and repairability. There are trade offs in sheen levels:

  • a glossier sheen tends to resist marking and is easier to clean, but tends to highlight defects making them more difficult to repair.
  • Flat or satin finishes, on the other hand, touch up easier, but are not as durable or easy to clean.

Here is where the binders (see below) play their part and where your choice comes in.

For ceilings, flat sheen is most common because there is little cleaning and any ceiling lights won’t reflect easily off problem areas. For the walls in bedrooms, living rooms and hallways, most people split the difference and go with eggshell because there is some touch up and some cleaning. For the walls in kitchens, bathrooms and around windows and doors, use semi-gloss or gloss, because there is where you’ll have the most cleaning problems with dirty little fingers.

8) References. Learn from the experience of others who have painted on similar surfaces. Ask them what performs well over time and what doesn't.

Subtle differences in application can make major differences in paint performance. Also, paint manufacturers are constantly changing their formulas, so networking with other painters about what’s current can be very useful.

9) Warranty. Reputable companies stand behind their products and provide good support if issues arise.

Longer warranties don't always mean the paint is better. After all, most manufacturers only replace the paint if there is a problem, and not the labor which is the expensive part. Buy high quality paint from stores that turn inventory regularly and keep good records of your purchases.

Where and how to do research on paint?

First, consult with the manufacturer's website to see where you can find information about ingredients, pigments, binders and the percentage of solids contained in the paint.

Much of this information can be located in the Material Safety Data Sheet (MSDS).

  • Here you’ll also find information about key ingredients especially their relative quantities by volume and weight.
  • Why is this important?

Because the solids content is a good measure of quality. The more of it, the better the paint, but also the more expensive it becomes. The solids content is what is left behind when the paint dries. A thicker film usually means a longer-lasting, more durable finish. But what is the content or ingredients of paint?

What is paint made of?

(The following has been drawn from Wikipedia)

  1. Pigments, such as titanium dioxide, and fillers
  2. Binders such as polymer resins
  3. Liquids such as diluents or solvents
  4. Additives such as thickeners, defoamers, wax, surfactants, UV absorbers, biocides, etc.

Pigments and fillers
Pigments are granular solids dissolved into the paint to contribute color. Fillers are granular solids used to impart toughness, texture or to reduce the cost of the paint. Some paints also include dyes instead of, or in combination with, pigments.

Pigments are classified as natural or synthetic. Natural pigments include clays, calcium carbonate, mica, silicas and talcs, while synthetic pigments include engineered molecules, calcined clays, blanc fixe, etc. Hiding pigments make paint opaque and protect the substrate from the harmful effects of ultraviolet light. These include titanium dioxide, phthalo blue, red iron oxide and many others. There is currently some controversy surrounding the safety of titanium dioxide, which has replaced most toxic lead pigments since the late 70's.

Fillers are a special type of pigment that serve to thicken the film, support its structure and increase the volume of the paint. Fillers are usually cheap because they include inert materials such as diatomaceous earth, talc, lime, barytes, clay, etc. Floor paints that will be subjected to abrasion may contain fine quartz sand as filler. Not all paints include fillers; on the other hand, some paints contain large proportions of pigment/filler and binder.

Binders or resins
The binder, sometimes called a vehicle, is what forms the film or coating. The binder imparts adhesion, and strongly influences the sheen, durability, stain resistance, crack resistance, flexibility and toughness. In most cases, the higher the quality of the paint, the higher the paint’s ratio of binder to pigment.

Some typical binders include natural or synthetic resins such as acrylics, alkyds, vinyl-acrylics, vinyl acetate, polyurethanes, polyesters, epoxy or oils. Binders are categorized according to the mechanisms for drying or curing. Drying means the evaporation of the liquid solvent or thinner, but it also refers to an oxidative cross-linking of the binders which is identical to the process of curing. Most paints dry through this cross-linking process rather than through evaporation.

Latex paint is a water-borne dispersion of tiny polymer particles (binder). The
term "latex" in the context of paint refers to an aqueous dispersion and not the ingredient rubber (as it has been historically identified). Latex paints cure by a complex process where the water, and then the coalescing solvent, evaporate and fuse together the latex particles. The resulting structure of paint is irreversibly bound into a network that will not re-dissolve in the solvent/water that originally carried it.

Manufacturers use many types of binders, depending on where and how the paint is to be applied. Different binders can be used to improve the paint’s resistance to moisture permeability, sunlight exposure, damage from abrasion, adhesion to the surface and flexibility. In most paints, the pigment and binder solids account for between 25 and 50 percent of the total volume of the paint. The majority of the remainder of the paint’s volume is the liquid carrier.

Liquids: diluent or solvent
The liquid portion of paint acts as the carrier for the pigments and binders. It is volatile and does not become part of the paint film when dry. It also controls flow (viscosity) and application properties of the paint.

In the case of water-based paints, water is the main diluent. In the case of oil-based or alkyd paints, the diluent can be made of organic solvents such as petroleum distillate, esters, glycol ethers or combinations of organic solvents such as aliphatics, aromatics, alcohols, ketones and white spirits.

Diluents help to keep the pigments and binders in suspension, but their primary function is to reduce the cost of the paint. Higher quality paints have lower levels of diluents.

Additives
Paint can have a wide variety of miscellaneous additives, which are usually added in small amounts, yet they provide a significant effect on the product. Some examples include additives to modify surface tension, improve flow properties, improve the finished appearance, increase wet edge, improve pigment stability, impart antifreeze properties, control foaming, control skinning, etc. Other types of additives include catalysts, thickeners, stabilizers, emulsifiers, texturizers, adhesion promoters, UV stabilizers, flatteners (de-glossing agents), biocides to fight bacterial growth and the like. Additives normally do not significantly alter the percentages of individual components in a formulation.

How do you tell quality paint?

Quality paints contain both the best pigments and binders, but in addition, they contain more of these solids than lower quality paints. 

Economy paints provide hiding by using less pigment and extending it with fillers like clay or calcium carbonate that will have good hiding capability initially but lose their hiding capabilities over time-—particularly when exposed to weather.

Prep, prime, paint 

Finding the right paint for your application requires research and skill but once you've found it, your real job has just begun.

No matter how good your paint might be or how much you paid for it, it cannot succeed without proper preparation, priming and good painting techniques. Everyone knows that a good paint job is 50% prep and 50% paint.

  • A smooth, dry, clean, neutral pH surface along with a good primer will provide the basis for good adhesion and yield long lasting results.
  • Don't ask your paint to do your primer's job. 

We will cover paint preparation and primers in another article.

 

 

For More Information:

Green Home Guide's Know How article Paint Like a Green Pro gives practical tips for painting your home.

Read Selecting Green Paint for an overview of paint options and environmental and health considerations.

Do you have a question about greening your home? GreenHomeGuide invites you to Ask A Pro. Let our network of experienced green building professionals – architects, designers, contractors, electricians, energy experts, landscapers, tile & stone specialists, and more – help you find the right solution.