What is the best exterior paint?
That s a hard question to answer. Paint that performs well on wood might not perform well on metal. Paint is an ever-changing industry. Before 1978 many paints contained lead. The lead based paint is toxic for the environment and harmful to most life forms. Although from what I have seen in the field, paint with lead lasted longer and was more durable than any of the paints manufactured today. Not having lead in paint is a great thing, yet pressure from environmental agencies to reduce harmful components such as lead and vulgar organic compounds (VOC’s) creates a challenge to make a product that is both safe and durable.
What makes a paint good or better than a different paint is what the paint is actually made of. So let talk about what is actually in paint. For this discussion I am going to focus on water-based latex paints because it makes up the majority of paints used and sold today. I will make another blog about solvent-based paints, commonly referred to as oil-based paints or “alkyds” later. Furthermore, for this discussion I want to focus on paints designed for the exterior of homes. There are 5 basic raw materials that make up paint. They are solvents, thickeners, additives, pigments, and binders or resins.
Solvents & Thickeners
The solvents and thickeners are used to help with the application process. The solvents make the paint a liquid and after the paint is applied they evaporate, leaving behind the solid substances within the paint. The 2 most common solvents used are water and oil, hence water-based or oil-based paints. The thickeners help hold the wet paint in suspension, allowing you to increase the thickness of the coat without runs or sagging.
Additives can do a variety of things. Usually the additives are there to prevent an unwanted property of the paint. The most common additives used are deodorants to mask the smell, fungicides to prevent fungus growth, moisture scavengers to prevent gelling, silicones and waxes for mar resistance, and UV absorbers.
Pigments have 3 basic functions in paint, to provide color, sheen, and anti-corrosive properties. The most common pigments that provide color are titanium dioxide for white, iron oxide for red and yellow, and chrome oxide for green. These are “inorganic” pigments, and can be used to achieve most colors, however to make very rich bright colors “organic” pigments usually by-products of petroleum derived from chemical processes are used. These can produce bright blue, green, yellow, orange, violet, and magenta colors. Carbon is often used to produce deep blacks. These pigments are a big part of the manufacturing cost is often why some paints are more expensive than others. Generally the “organic” pigments are extremely more expensive than the “inorganic”, but can produce properties and colors that the “inorganic” pigments can’t, if your going to choose a vibrant color you should spend time researching the pigments used in the paints you are considering.
Pigments that contribute to sheen and barrier properties are barytes, talc, mica, silicas, calcium carbonate, and clays. For a high quality exterior paint you want barrier protection talc and mica are best for this. The other sheen pigments are necessary but since calcium carbonate and clay are cheap, usually high amounts of this are not a sign of high quality. Anti-corrosive pigments are more common in industrial paints, since I am focused on exterior paint for homes don’t want to spend time here, if you are painting metal zinc chromate will resist rusting.
Binders & Resins
There are three common types of binders in paints they are acrylic, alkyd, & epoxy all of which are polymers (resins). When dealing with exterior house painting acrylic is the best type of resin for combating the outside elements. Typically the higher percentage of solids in the paint the better the paint, however some manufactures will put cheap fillers in the paint to get the solids content higher. The type of solids you want to look for is “all-acrylic” or 100% acrylic. All acrylic binders are more weather resistant than vinyl or vinyl-acrylic, so if possible check to see what kind of binders are in the paint and how much is in the paint.
In conclusion, the best exterior paint depends on what you are painting and where you live. If you live in a place with lots of moisture and little sunlight you want a paint that is mold and mildew resistant. If you live in a dry climate with lots of sunlight you want paint that has fade resistant pigments. If you live in a climate where the temperature fluctuates a lot you want a paint that is flexible and made of 100% acrylic resins. Figuring out what is in the paint can take some time and research, most exterior paints will last 7-15 years before you need to repaint. Just because a label says it’s high quality paint does not mean that it is true. I recommend checking to see the % of solids in the paint, then asking for the product data sheet to see what type of pigments and resins are used, then make a decision based on your specific climate and budget.