When it comes to exterior paint, “best” depends on a myriad of factors. Answers to some core questions can help guide your decision-making process and give you a better idea of what you’ll need for your project. They can’t be summarized, so we’re going to take a deep, relatively technical dive into the things to consider when choosing the perfect exterior paint for your project over a series of articles—starting with this one.
How Long Do You Expect Your Exterior Paint Job to Last?
Longevity is the primary motivation when choosing an exterior paint, and for good reason. Finding the right product isn’t easy to do nor is it cheap, so you don’t want to do it every year.
In order to temper expectations, it’s important to understand that, at a chemical level, inert substrates (surfaces) will always hold exterior paint better than active or living surfaces, such as wood. Inert surfaces allow for a more stable chemical and mechanical bond. This basic chemical concept means that not much will last long on wood, and you’ll need to factor in regular maintenance.
Inert surfaces offer more promise. To narrow down the scope of this statement, we’ll define durability simply as adhesion. Proper paint preparation is vital for a lasting paint job; applying the correct paint for the surface you’re looking to revamp is equally as important. This leads us to our second question.
What Surface Are You Painting?
This is by far the most important variable to consider. Although most exterior latex paints are made to be applied on just about any surface, a jack of all trades is a master of none. At a technical level, adhesion happens when the surface tension of the paint is lower than the surface energy of the surface to be painted. If the paint doesn’t properly coat or wet the surface in its entirety, you’ll never get the proper mechanical and chemical bond required for a long-lasting exterior paint job.
How you apply the coating also has an impact, which we’ll talk about next issue. Beyond adhesion, we’ll need to dive a bit deeper to establish what other properties to look for on the most commonly painted exterior surfaces to ensure a long-lasting paint job.
Paint needs to be washable, yet slightly flexible, which creates somewhat of a paradox. It needs to be flexible enough not to crack but not too flexible that dirt pick up becomes an issue. Aesthetically, you’ll want to choose a gloss that’s not too flat but not so glossy that it enhances the appearance of any defects in your siding. In order to achieve these properties, the optimal conventional paint will be a self-cross-linking exterior paint. These types of resins create a tighter bond, allowing for better adhesion, washing, and flexibility.
Doors are high-traffic items that require good scratch resistance. The optimal paint for this would be an enamel. Water-based polyurethanes are an excellent choice where enhanced flexibility and fade resistance is needed. Alkyd enamels could also do the trick if hardness is the primary desired property.
This surface requires elasticity; breathability; and, ideally, washability. Ideally because, back to the elastic example, having a flexible coating that is washable is somewhat paradoxical. Although you can use an exterior latex paint on stucco, elastomeric coatings are better suited.
All large paint manufacturers make these types of coatings, but the challenge they face is price. Elastomeric coatings need to be applied very thick to achieve the desired coverage, so you can expect a gallon to cover only between 75 and 100 square feet. Paint manufacturers will use additives, such as calcium carbonate (essentially chalk), to thicken their products without drastically increasing the price. The paint then becomes less washable, and that undesirable powdery finish will more quickly occur as the paint starts to degrade. Still, it’s important that you don’t purchase on price alone.
Look for our next article to learn more about application of the right paint for your project.