As covered in our Exterior Paint FAQ, painting a house is no small task, and it’s crucial to understand which materials are most appropriate for your project. We expect a lot from a brand-new paint job: color quality, resistance against extreme weather conditions, and most importantly, a product that will last for years to come. The most promising paints are those packed with high-quality resins, pigments, and additives. For example, look for paints labeled “100% acrylic latex”, as these give unmatched results and are a far better choice than those made with vinyl resins or acrylic blends. This guide is here to help you compare and choose the best products for your home, from various blends to how much to purchase.
What’s in the Can?
Blends vary, but all exterior paints come with the same basic ingredients:
Solvents: Quick-to-evaporate liquids keep binders and pigments in suspension.
Pigments: Powdered minerals and man-made colors give paint its hue and opacity.
Additives: Control dry time, leveling, mildew, and more.
Binders: These resins coalesce to form the paint film after the solvents evaporate.
Top-ranking paints are those made with 100% acrylic resins. However, the proportions of ingredients, coverage rates and dry-film thickness can vary significantly. This data can be found on technical data sheets (TDS), which is provided for free by all manufacturers online.
Decoding the Lingo
Solids: All the resins and pigments left behind after the solvents evaporate. A higher solids ratio may indicate a good paint if its resins and pigments are of high quality.
Dry-film thickness: Each paint is formulated to attain a certain thickness, measured in mils, when brushed or rolled out. One mil is one-thousandth of an inch.
Coverage: This number goes up as the film thickness goes down. Use it to calculate how much paint you need to buy.
VOCs: Volatile organic compounds—solvents that adversely affect our lungs and air quality. Federal regulations limit the amount of VOCs to 250 grams per liter in exterior flats and 380 in glossier coatings.
Due to a push for the use of latex paints in the 1950s and increased restrictions on high-VOC solvents, there’s been a steady decline in the use of oil-based paints in the U.S. Nevertheless, oils come with a gloss, smoothness, dirt resistance, and hardness that water-based paints can’t match. Thus it still makes sense to use oils in some outdoor applications: doors, wrought iron, and other details. Oil’s durability make it an excellent choice for porch floors.
Paints for Masonry
When painting masonry work (brick, stone, stucco), you need to be cautious with your paint choice. Whichever one you go with must allow water vapor to pass through it. For this reason, avoid oil-based finishes, as they trap moisture, wreak havoc on mortar, and quickly fail. Choose one these instead:
Acrylic: High-end house paints do allow moisture to escape but need an alkali-resistant primer to protect them from cement’s high pH.
Lime: An ancient coating formula of slaked quicklime and mineral pigments gives masonry a rich, old-world look. Its velvety finish wears off easily and needs to be reapplied about every five years.
Mineral: Instead of resins and solvents, mineral paints use silicates, which chemically bond to masonry to form a completely breathable, extremely durable skin. Two coats should last 50 years.
Pick a Sheen
A paint’s gloss, or lack thereof, is about more than just your preferred aesthetic. It also affects how paint performs and where it should be applied.
Satin/eggshell: Best for siding because it’s a low-reflective finish that’s good at hiding surface imperfections. It has a slight gloss, so it stays cleaner, is more easily washed, and stands up to abrasion better than flat or matte paints.
Semigloss: P This shinier sheen is easier to clean, more durable, and more moisture resistant than a satin or eggshell paint. Best for trim, particularly on window sills, which take the brunt of the weather.
Highgloss: This resin-rich formula is resilient and dirt-repellent, and adds richness and depth to colors. It also magnifies surface imperfections and requires skillful application. Use it sparingly; best for shutters, doors, and surfaces you touch or come in close proximity to.
How Much to Buy
To calculate how many gallons you need for siding, measure and add up each wall’s total square footage, including windows and doors, and divide by 90 percent of the coverage rate printed on the can. For trim paint, use the equation shown.
(This information originally appeared in This Old House magazine. Author // Thomas Baker.)