What is a coat of paint? It might seem like a silly question. Isn’t it obvious? Everyone who has ever dipped a brush into a can of paint knows what a coat of paint is, right? But what is the right amount of paint? That’s much more complicated. Some paints are supposed to be applied thin, while others are applied thicker. Some thinner paints are intended to be applied in multiple coats. Some surfaces need to have a primer coat, or some type of basecoat, and then one or two applications of the finish coat.
How can you know in each circumstance how to properly paint a surface? The answer, of course, is to follow the instructions. Paint manufacturers print a concise set of instructions on the paint can label. And most manufacturers provide a much more detailed product data sheet (PDS) on their website. You will find a sample of a PDS at the bottom of this bulletin. If you do your own painting, please take the time to read the label. If you have more questions, find the PDS.
The consumer may not want to be a painting expert, but he needs enough information to know if he is being told the truth, a falsehood, or something in between. For example, he reads the label on a gallon can of paint at the local home improvement store that claims this paint is a one-coat paint. It is one of the more expensive paints. But it will save a lot of time over a two-coat paint, won’t it? Better read the entire label. If you have a significant color change, it won’t cover in one coat. If you are painting an unpainted surface, you will need more than one coat. If you are painting a rough or porous surface, it will likely require more than one coat.
If you are hiring a painting contractor to paint your home, how can you be confident in his workmanship. Will he put enough paint on the walls? Will it be properly applied? We routinely hear stories from homeowners about unscrupulous painters who claim they applied two coats of paint when in reality, they rolled over a wet wall of paint with a second pass. By industry standards that’s still one coat of paint. The first coat must thoroughly dry before a second coat can be applied. There is a process called back rolling where the first painter applies a coat of paint with a sprayer. He is followed by a crew member with a roller. The second paint “back rolls” the sprayed paint. They may tell you that constitutes a second. According to the industry standards, it doesn’t.
Fortunately for the consumer and the contractor, the Painting Contractors Association (PCA) provides an industry standard that defines what constitutes “a properly painted surface”. The PCA standards helps facilitate consumer and contractor communication. It provides a framework for understanding and agreement. It instructs the contractor what information and detail need to be included in a project proposal so that the consumer knows what to expect.
Painting Contractors Association Industry Standards
PCA developed its Industry Standards to make the painting industry transparent to both painting contractors and consumers. The purpose of this bulletin is to aggregate the pertinent information from the very lengthy standards document into a succinct tech bulletin that defines what is a coat of paint and how much paint is necessary for a full coat of paint in order to have a properly painted surface.
The different kinds of coatings are defined.
PCA P9 – Definition of Trade Terms
3.1.17 ARCHITECTURAL COATING: Coating intended for on-site application to interior or exterior surfaces of residential, commercial, institutional, or light industrial structures as opposed to factory-applied or industrial coatings.
3.1.25 BARRIER COAT: A coating or primer designed to shield or block the chemical or solvent interaction between a substrate and a finish coating.
3.1.40 COAT: A layer of paint, varnish, lacquer, or other material that is applied according to the paint manufacturers’ wet film thickness range and then allowed to dry. To back roll or apply a wet-on-wet film still constitutes a single coat.
3.1.85 FIELD COAT: Coat or coats of paint that are applied at the jobsite. Also known as field application.
3.1.86 FILLER: A heavily bodied material used to fill voids, holes, pores, depressions, etc., in a substrate.
3.1.91 FINISH COAT: The last coat applied in a painting operation. A finish coat is formulated specifically for environmental resistance and appearance.
Standards regarding primers, basecoats, and finish coats.
PCA P19 – Definitions and Applications of Decorative Finishes
5.1 Prior to the application of primer and base coats, surfaces shall be inspected and approved in accordance with PCA Standard P4 – Inspection and Acceptance of Surfaces Prior to Painting and Decorating
5.2 The specifications shall indicate the number and type of primer and base coats to be applied by the Painting Contractor in the contract documents.
5.3 The Painting Contractor shall apply the specified paint coats to produce a properly painted surface as defined in PCA Standard P1.
The definition of a properly painted surface.
PCA P1 – Touch Up Painting and Damage Repair, and Definition of a Properly Painted Surface
2.4 The Painting Contractor will produce a properly painted surface. A properly painted surface is one that is applied in accordance with the contract documents, the manufacturer’s printed Technical Data Sheet(s) and is uniform in appearance, color, texture, hiding and sheen. It is virtually free of foreign material, lumps, skins, runs, sags, holidays, misses, or insufficient coverage. It is also a surface free of drips, splatters, spatters, spills, cracks or overspray caused by the Painting Contractor’s workforce or its assigns. In order to determine whether a surface has been properly painted it shall be examined without magnification at a distance of thirty-nine (39) inches or one (1) meter, or more, under finished lighting conditions and from a normal viewing position.
Wet film thickness and dry film thickness (DFT)
Many production flat wall finishes are formulated to provide reasonable hide and uniformity when applied at a consistent 10 wet mils* (combining total applied coats), allowing for a minimum dry film thickness (DFT) of 3 mils. To achieve reasonable hide, film thickness will vary by product, depending upon both the volume of the product’s solids, and the performance properties of the specific combination of solids used in the formulation. Your supplier can recommend the target milage.
* A ”mil” is one thousand of an inch (.001”). For comparison, the thickness of a sheet of copier paper is approximately 3 mils. Typical interior or exterior wall paint is applied at about 10 mils thick, and then dries 3 to 4 mils thick.
Product Data Sheet (PDS)
A PDS is information provided by the paint manufacturer about their product with very detailed information, which includes instruction on the proper application of their paint. Following is a portion of the PDS for a Sherwin Williams exterior paint that is recommended by MTS Painting. This selection pertains to primers and finish coats. Other information excluded from this selection concerns application, preparation, cautions, etcetera. You can read the entire PDS here: Latitude™ Exterior Acrylic Flat (sherwin-williams.com). A painting contractor is expected to know this information. If he follows the manufacturer’s instructions, he will provide his customer with a properly painted surface.
SPECIFICATIONS
Latitude can be self-priming when used directly over existing coatings, or exterior bare drywall, plaster and masonry (with a cured pH of less than 9). The first coat acts like a coat of primer and the second coat provides the final appearance and performance. Please note that some specific surfaces require specialized treatment.
Use on these properly prepared surfaces:
Aluminum & Aluminum Siding1, Galvanized Steel: 2 coats Latitude Exterior Acrylic
Concrete Block, CMU, Split face Block: 1 coat Loxon Acrylic Block Surfacer 2 coats Latitude Exterior Acrylic
Brick, Stucco, Cement, Concrete: 1 coat Loxon Concrete & Masonry Primer (if needed) or Loxon Conditioner (if needed) 2 coats Latitude Exterior Acrylic
Cement Composition Siding/Panels: 1 coat Loxon Concrete & Masonry Primer (if needed) or Loxon Conditioner (if needed) 2 coats Latitude Exterior Acrylic
Plywood: 1 coat Exterior Latex Primer 2 coats Latitude Exterior Acrylic
Vinyl Siding: 2 coats Latitude Exterior Acrylic
Wood (Cedar, Redwood): 1 coat Exterior Oil-Based Wood Primer 2 coats Latitude Exterior Acrylic Knots and some woods, such as redwood and cedar, contain a high amount of tannin, a colored wood extract. For best results on these woods, use a coat of Exterior Oil-Based Wood Primer.
Wood Composition Board – Hardiboard: Because of the potential for wax bleeding out of the substrate, apply 1 coat of Exterior Oil-Based Wood Primer and then topcoat. 1 On large expanses of metal siding, the air, surface, and material temperatures must be 50°F (10°) or higher. Standard latex primers cannot be used below 50°F (10°C) or above 100°F (37.7°C). See specific primer label for that product’s application limitations.
Other primers may be appropriate.
When repainting involves a drastic color change, a coat of primer will improve the hiding performance of the topcoat color.
For more information about this topic or any other painting topic, please contact us.
