Applying an all purpose primer or a primer formulated for a specific use plays an important role in the area of painting preparation. Primers are used to improve the conditions of new and previously painted surfaces which are to receive new coats of paint. Some of the benefits of using primer include the following:
A coat of primer acts as a base coat that allows subsequent coats of paint to function properly. Unfortunately, no single primer can be used for every painting application. Rather, a wide variety of primers exist, each formulated for a particular objective. Some primers are devised for very specific uses while others, such as an all purpose primer offer a wider variety of applications.
Primers can be classified according to location, use, and solvent base. Consider each one of these categories when choosing a primer.
Primers, much the same as paints can be classified according to where they should be used. Interior primer should only be applied to interior surfaces while exterior primer is rated for exterior use only. All purpose primer and some specific use primers are often recommended for both interior and exterior applications.
Types of Use
A straightforward way to choose the right primer is to first identify the intended use. Each type of primer is formulated to be compatible with certain substrates. For example, you would not use the same primer on ferrous metal as you would on new drywall. An all purpose primer can be used on a wide variety of surfaces but it is not necessarily the best choice for some painting applications. Refer to the list of materials/substrates with corresponding primers for recommendations.
Primers can also be classified according to solvent base. Solvent bases among primers typically include the following:
Primers belonging to different solvent bases have their unique characteristics. Each primer base offers some positive attributes as well as some drawbacks.
Latex/Acrylic primer is water base primer widely used for all types of substrates. The ease of use and superior performance make water base primers the most popular primers on the market. The drying process for latex/acrylic primers requires the water (solvent) to completely evaporate so that pigment particles can properly coalesce with the acrylic resins. This forms a continuous surface film with microscopic pores. In turn latex/acrylic primers have greater flexibility as well as the ability to breathe giving them a clear advantage when used over substrates subjected to moisture.
Latex primers do have some limitations. Extreme temperatures and high humidity can have a negative effect on both application and the cure time. Cold temperatures and high humidity can interrupt the drying process adversely limiting the primers ability to function properly.
Oil base primer also referred to as alkyd primer is thinned with mineral spirits. These types of primers are commonly used to prime wood and ferrous metals. They are also used to a lesser degree for a variety of other materials. Some attributes of oil base primer include strong adhesion, ease of sanding, good filling properties, and the ability to seal water soluble stains. As the mineral spirits evaporate in the drying process, the pigments come together with the resins used in oil base primer to form a hard, almost impervious surface film.
Oil base primers do have the tendency to become somewhat brittle over time. This makes them vulnerable to blistering and peeling, especially when applied over damp surfaces or substrates where water transference is an issue.
Pigmented shellac primer offers superior stain sealing qualities. The denatured alcohol readily evaporates allowing an impervious surface film to form. The rapid dry time helps to lock in all types of stains and odors. The alcohol base kills bacteria upon contact. Because shellac primers are sensitive to extreme heat and their surface film is a bit inflexible, they are recommended for interior use only. Some limited exterior use is okay.
Lacquer primer is an interior primer designed to be used over new or previously lacquered wood surfaces. Some lacquer primers are available for metal substrates. Professional painters often use lacquer primer for high production painting because of its fast dry time and ease of sanding. Lacquer primers tend to be somewhat brittle and are subject to flaking and peeling.
Water base acrylic primers have significantly improved in recent years. Besides the benefits of the low VOC content and the easy clean-up, their ability to seal stains and adhere to hard glossy surfaces has approached that of pigmented shellac and oil base primers. With that being said, it still is a good idea to use the pigmented shellac and oil base primers for severe conditions.
Using an all purpose primer offers a clear advantage for some painting applications. It gives you the ability to prime several different substrates with the same primer. This can be a major timesaver insofar as using a single product requires less set-up and clean-up time compared to that of multiple products. The purchase of one all purpose primer eliminates the need to buy several different primers, resulting in a material savings.
Whichever primer you choose, it is important to select the right primer in order to accomplish your objectives. An incorrect primer can create a negative outcome. Always refer to the product label for proper use.