Choosing the correct primer is key to final outcome of a paint job.
by Robert Simpson
and overlooked areas of the painting business is the subject of primers, sealers and undercoats. Contractors often fail to consider primers and sealers with any real seriousness, choosing rather to think of the basecoat as a good place to get rid of that leftover paint. Like most things, with primers and sealers you get what you pay for.
Primers in general are like a forgotten product in the paint contracting business. Many contractors pay far more attention to topcoat „ how glossy it is and if it is the right texture. But putting an expensive topcoat over a cheap or even wrong primer is not going to hold up.
"Primers solve problems," says Andrew Kinnen, product manager, architectural coatings for Cleveland, Ohio-based, The Sherwin Williams Company. The right primer or sealer can improve the enamel finish, mask or prevent certain stains, reduce or inhibit corrosion, prevent or diminish water damage, prevent scaling or peeling and allow paint to adhere to most difficult surfaces.
"Contractors can face a myriad of surface problems that without the use of primers would prevent them from achieving the finish the customer demands and expects. If substrates were perfect, there would be no need for a primer, but such surfaces are few and far between," says Kinnen.
Using the right primer can also influence job efficiency. Primers reduce surface preparation expense, improve coverage, speed top coating and reduce callbacks „ all of which lead to significant savings in time and money.
But because of the overwhelming number of specific products for specific tasks, choosing the correct primer or sealer can also be a real problem. Some basic knowledge of the intended function of primers and sealers may help, but the best solution for choosing a primer or sealer is still to ask the advice of suppliers and read instructions.
One of the complicating factors is the terminology. Primers, sealers and undercoats are words almost always used interchangeably to describe this category.
Generally, undercoating is a broad term used to mean a number of things including primer or sealer. And there are significant differences between primers and sealers.
Primers are generally products that have high pigment content, or high pigment volume concentration (PVC) while sealers has lower PVC and is generally clear.
The real difference between a routine primer and sealer is that a primer is intended to link with the topcoat on the substrate. Primers are used in preparing surfaces for painting, and they differ from paint in the type of resins they contain, and the amount of resins. Primers usually have higher resin content than paint.
A sealer performs a similar task in linking the topcoat to the substrate, but those with high resins are designed to seal the porosity of the substrate. Without a sealer the substrate would absorb the topcoat. Sealers have high binders and low pigments. All good primers perform the basic functions of sealing, hiding and binding to form a firm foundation for topcoats. Modern research and development has allowed for the emergence of new primer technologies-products that not only provide the basics but attack specific problems. These all-purpose primer-sealers have PVCs in the range of 25-50 range „ the lower the number of PVCs the better the filling action or high volume of solids (the only time a primer gets a very high PVC and low resin is when it is developed to specifically hide something).
From these basic formulations, a countless number of primers and sealers, each with their own specific task, are available. But choosing the right primer is not as difficult as it appears. "If you know the job's scope and limitations-use this knowledge to make the proper primer decision," says Bob Senior, president of Somerset, New Jersey-based William Zinsser and Company Limited.
Selecting the appropriate primer is one of the cardinal rules of surface prep.
Selecting the right primer in specific situations depends in large part on its composition. There are three types of primers „ water-based (acrylic), oil-based (Alkyd) and white pigmented shellac. Sealing primers seal, lock out and hide stains, graffiti, tannin bleed and damage from other trades. Some primers in this category seal out moisture and efflorescent salts, or block odors. Such primers are ideal for delivering best appearance of flats and enamels on walls, doors, trim, exterior siding and fresh masonry.
Primers in this a category are generally 100 percent acrylic. Most effectively seal out common stains found in architectural settings. Perfect for rehabilitation work, this category tends to ensure smooth uniform topcoat.
On wood surfaces, where the wood's cellulose can hold staining tannins, pitch, resin and other enemies of paint, the best defense is to help prevent most of these stains and to invest in a top-quality stain-blocking primer. Redwood, cedar, fir are especially prone to tannins, which are water-soluble dyes in wood, bleeding through and discoloring topcoats. Alkyd primers tend to seal in the stains, as do some latex-based formulations.
Bonding primers tightly anchor topcoats to slick and hard-to-paint surfaces, promoting durable adhesion and reducing prep time. These latex primers are best used under flat and enamel coatings on such substrates as PVC pipe, laminates, galvanized metal, hardboard, plastic trim and molding, and green board, varnished or enameled surfaces.
Another category of primers maximize gloss and leveling of the topcoat. They also provide excellent holdout on multiple substrates of varying porosity to ensure uniformity and excellent image, otherwise know as gloss. Use this category as a primer under enamels or flats on walls, doors, drywall, plaster, and wood to eliminate dull spots, or shiners.
The 100 percent acrylic latex versions of these primers tend to be fast drying and ideal for all-around, general use, while allowing them to be sanded „ if desired „ two hours after application. For those painters more traditionally bound, oil-based primers in this category are an alternative when ensuring that enamel topcoats develop their full gloss on interior wood. Such primers penetrate the paintable surface, sealing and protecting it to promote paint adhesion. Topcoat gloss is maximized with uniform color and shine eliminating the need for extra topcoats. These primers are particularly useful on new or repaint jobs; interior woodwork and trim; crown molding, doors, furniture, and on walls under wall covering.
Primers ensure uniform color and appearance, as well as hiding the substrate, previous color and surface marks. These primers, when used under flat enamel coatings on walls and ceilings, maximize topcoat touchups, and increase the effectiveness of topcoats, therefore reducing application costs.
These general-purpose wall primers improve appearance and performance. They can seal drywall and hide stains. Also effective as a barrier coat for dramatic color changes, this category can also work well as a sealer under and/or over sprayed-on textured wall surfaces.
Bonding primers tightly anchor topcoats to slick hard-to-paint surfaces promoting durable adhesion and reducing preparation time.
Surfacing primers smooth the substrate and permit uniform topcoat sheen. These products achieve this by filling, leveling and sealing porous, rough, uneven and dissimilar surfaces. These primers are ideal for use under flats and enamels on new drywall construction, heavy renovation or restoration work and on concrete block.
High-build drywall primers fill and eliminate minor surface defects like paper fuzz, scuffs, nicks, pinholes and sanding grooves, saving expensive repair and patching time on rough seams and damaged sheetrock prior to painting. Designed to uniform and equalize the porosity of new construction wallboard paper and drywall compound, high-build primers allow for a consistent topcoat with no telegraphing tape joints of lashing enamels under mud seams. A second type in this category „ block fillers „ fill, seal and ensure the uniformity of rough, porous unpainted and textured concrete and cement surfaces. These thick formulations bridge pinholes commonly found in concrete surfaces for a smooth, uniform finish coat with maximum adhesion, appearance and long-term performance.
Today's primers have come a long way „ both in variety and performance. There are several good all purpose primers as well as new primers developed as solutions for hard-to-paint substrates. It is recommended before beginning any job a consultation with a local supplier about the correct primer will deliver a topcoat with the ultimate in appearance, value, efficiency and profitability.