What are the trade-offs between the two enamels?
Traditionally, oil-based (technically known as “Alkyd”) enamels have been the coating of choice for painting interior trim and doors. There are several reasons for this. Among them are glossier appearance, increased durability (compared to acrylic enamels), and a longer drying time that allows brush marks to “flow out”.
One disadvantage of oil-based enamels is that they yellow over time. This is particularly true in areas such as Laundry Rooms, closets, pantries, etc. that do not receive much light. This can make touch-up difficult, if not impossible, since even having touch-up paint left from when the job was initially completed does not guarantee a match to the appearance of paint that has been “up” for a substantial amount of time.
Another disadvantage of oil-based enamels is that they require mineral spirits (“paint thinner”) to clean equipment after painting. Acrylic enamels are waterborne, so clean up is not only much easier, but more environmentally-friendly, too.
But the major disadvantage of oil-based enamels is their high VOC content. VOC stands for Volatile Organic Compounds, and these are the chemicals that are of concern from environmental and health points of view. LEED guidelines for “green” paints are that they must be under 150 grams/liter for non-flat sheens. A quick look at the data sheet for one major manufacturer’s popular oil-based semi-gloss trim enamel reveals that it contains 380 grams/liter — more than twice the “green” limit. California has some of the strictest air quality laws in the country and has already banned used of oil-based enamels for most uses. The rest of the country is going that direction and oil-based enamels will phased-out for most applications within a few years.
Acrylic enamels do not yellow over time, and have much less VOCs. Why then are they not more commonly used? As mentioned above, they are not as durable, do not tend to be as lustrous, and they show more brush marks. In addition, Acrylics will generally not adhere directly to oil-based paint, although this is changing as paint manufactures recognize the need to switch over to acrylic enamels in the future and are going to work on the paint chemistry to create products having better adhesion. So painting over “traditional” oil-based enamel with acrylics may require a primer coat to create the proper adhesion.
Copyright 2009 Jeff Stec