New formulas reduce maintenance painting costs
The true cost of plant maintenance painting involves a number of factors, including materials, labor, and time.
Materials — The actual cost of the coatings used to paint a facility is the most obvious, but is often the smallest, expense associated with maintenance painting.
Labor — The cost to apply the coatings typically consumes a much bigger portion of the maintenance budget.
Time — In some cases, the largest costs of maintenance painting are idle labor, the loss of production, and other inefficiencies resulting from plant downtime. For example, in pulp and paper mills, downtime on a kraft paper machine can result in a loss of $50,000 an hour.
Fig. 1. Today’s industrial floor coating choices include acrylic, waterborne epoxy, and moisture cure urethane formulations. These offer distinct advantages compared to traditional solvent-based epoxy floor coatings.
Advances in paint technology have resulted in coatings that require less labor to apply, minimize disruption to the plant, and shorten downtime (Fig. 1). A larger investment for these materials may be money well spent. Technologies to consider are:
High-performance waterborne formulations that are easy to apply and clean up
Surface-tolerant coatings that reduce surface-preparation needs
Moisture-cure coatings that can be applied in cold temperatures or damp conditions
Dryfall ceiling paints that produce a dry, sweepable overspray.
Waterborne coatings offer significant application benefits. Their low odor enables application without an unpleasant paint smell that could affect nearby workers. Downtime can be limited to the structures being actively painted, so work in surrounding areas may continue unimpeded.
Waterborne coatings have high flash points, which reduces fire hazards. Application tools can be cleaned with soap and water, eliminating the high disposal cost associated with organic solvents, some of which are considered hazardous wastes.
New polymers allow today’s waterborne epoxy and urethane coatings to be abrasion, chemical, and moisture resistant at prices comparable to conventional coatings. Complementing these resins are additives that help the coatings overcome flash rusting so they can be applied directly to bare steel or directly to existing coatings.
Waterborne industrial maintenance coatings can be applied by brush, roller, or sprayer. Some waterborne technologies to consider are:
Waterborne acrylics for light-to-moderate industrial uses
Acrylic coatings are said to be the leading finishes used in the coatings industry as a whole, and they are rapidly overtaking alkyds, even in industrial uses (Fig. 2). They are noted for their excellent exterior color and gloss retention.
Fig. 2. Waterborne acrylic coatings have excellent exterior color and gloss retention as well as the ability to withstand exposure to mild chemicals and exterior weathering.
Acrylic resins are transparent and are resistant to changes in color over time. Because their main polymer chain is a carbon-to-carbon single bond, they are relatively inert and not as susceptible to chemical change as many other linkages. This makes them highly durable. In industrial coatings, acrylics are coreacted with other resins such as epoxies, vinyls, and isocyanates to become more flexible, durable on exteriors, and weather and water resistant, keeping the appearance of the coating fresh.
In terms of their application advantages, waterborne acrylics are fast drying, easy to apply, and low odor, with excellent adhesion and opacity. The thick, flexible film offers less cracking and peeling with the integrity to stand up to mild chemicals and corrosion.
Waterborne epoxies for light-to-moderate industrial uses
In the past, using a waterborne epoxy coating meant restrictions on temperature and humidity during application of the two-component coating. They had fair resistance to solvents and a tendency to chalk and fade. But new technologies overcome these drawbacks.
While the traditional waterborne coating cannot be applied below 50 F, waterborne epoxy can now be formulated to allow for colder temperature application — as low as 40 F — allowing for a longer application window as well as a faster cure.
Waterborne catalyzed epoxies now perform well compared to their solvent-based counterparts. They form a tight, dense film that is resistant to corrosion, mild chemicals, impact, and abrasion. In addition, they offer the application advantages of the other waterborne coatings, such as low odor, no fire hazard, ease of application, easy cleanup, and the ability to be applied over existing coatings. Some epoxies can also be applied directly to PVC and fiberglass reinforced plastic (FRP).
Waterborne urethanes for moderate-to-severe industrial uses
New urethane technology has resulted in a coating that uses a conventional resin with a water reducible polyol rather than an emulsion technology. This creates a film that is very flexible and dense. Waterborne urethanes provide excellent color and gloss retention on exterior surfaces.
Coatings for marginally prepared surfaces
Improper or inadequate surface preparation accounts for 80% of paint failures. Coatings for marginally prepared surfaces are designed for application over existing coatings or less-than-fully prepared surfaces, minimizing downtime. The specification and application of such coatings can accommodate limits on surface preparation without compromising coating performance.
Why are surface-tolerant coatings needed? The high cost of surface preparation and the time required for paint removal can contribute greatly to the cost of maintenance painting. Also, in manufacturing environments where the presence of blast particles in the air can damage sensitive equipment, thorough surface preparation may not be an option.
Surface-tolerant primers and topcoats are typically high-solids epoxies or epoxy mastics. Depending on coating type and application, they may be applied over rusted or pitted steel that has been cleaned using hand tools when blasting is not possible. Even surface-tolerant primers require surfaces that are clean, dull, dry, and in sound condition. Oil, grease, dirt, dust, loose rust, and foreign material must be removed prior to painting.
Surface-tolerant primers work by penetrating existing, tightly adhering rust to create a “tight” surface prior to subsequent coats. These coatings may be applied over white rusted and weathered zinc-rich coatings. They also can be used as high performance primer/sealers for masonry surfaces.
Typically, a surface tolerant primer is specified for areas where abrasive blasting cannot be performed due to the proximity of sensitive equipment. The surface is cleaned using hand or power tools to the SSPC-SP2 and 3 standards (see the sidebar titled “SSPC explained”). The surface-tolerant primer is then applied to a thickness of 2-3 mils dry film thickness (DFT). The primer penetrates into any remaining rust. The resultant surface is one that is ready to receive a high-performance topcoat.
Low-temperature and moisture-cure coatings
Fig. 3. Moisture-cure urethanes are useful for damp environments, because they are surface tolerant, quick drying, and applicator-friendly.
Moisture-cured urethanes, cold-cured modified epoxies and mastics, and inorganic zinc primers perform well when the temperature drops. Unlike conventional coatings, these systems are able to cure efficiently and form strong bonds to substrates in frigid and damp conditions (Fig. 3). While it is still desirable to schedule maintenance painting during favorable weather or in heated enclosures, sometimes painting during cold weather is unavoidable.
One of the more versatile coating systems for steel substrates is moisture-cure urethane. Surface tolerant, quick drying, applicator-friendly, and ready for application under adverse weather conditions, moisture-cured urethanes offer unique advantages in the continuous battle against corrosion.
While abrasive blasting to white metal (see the sidebar titled “What is white metal?”) is without question the best method of surface preparation, it is also the most expensive. Usually, cleaning using power tools is adequate for these types of urethanes.
Newton’s Law, often paraphrased as “what goes up, must come down,” can explain what happens when coatings are applied to the ceilings of manufacturing or warehouse areas. Too often, what comes down creates cleanup issues. But that’s not the case with dryfall coatings. They were developed to be spray-applied, with overspray drying to a powdery substance before reaching the ground.
This overspray is transformed from paint droplet to dust usually within eight to ten feet at 77 F and 50% relative humidity. The overspray-turned-dust can be easily swept away, allowing fast and easy cleanup of the job site.
There are two types of dryfall coatings available:
Standard-grade dryfalls, which provide two-coat coverage.
Premium-grade dryfalls, which require only half the amount of material to achieve the same degree of hiding as their older counterparts.
With just one pass of a spray gun, sufficient opacity can be achieved, even on new substrates, due to the high pigment content of these coatings. In addition, the newer, more advanced dryfall formulations offer excellent hiding even when wet, eliminating the temptation to apply additional, unnecessary coats of paint.
— Edited by Jack Smith, Senior Editor, 630-288-8783, email@example.com
More info The author is available to answer questions about this article. He can be reached at 216-515-5277, or at firstname.lastname@example.org . For more information on this topic, visit our website at plantengineering.com
SSPC-SP2 is the Steel Structures Painting Council’s specification for the cleaning of steel surfaces using hand tools. SSPC-SP3 is the specification for the cleaning of steel surfaces using power-assisted hand tools. Both standards are achieved when all loose mill scale, rust, paint, and other loose detrimental foreign matter are removed. Mill scale, rust, and paint that cannot be removed by lifting with a dull putty knife are considered adherent. Their removal is not required to achieve these standards.
Dos and don’ts for reducing maintenance painting downtime
Do identify the substrate type to be coated (carbon steel, concrete, galvanized metal, plastic, wood, or previously painted materials).
Do determine the corrosiveness of the environment.
Do identify surface preparation needs and impediments.
Do analyze the application situation. Consider the cost of downtime, adjacent structures, workers in nearby areas, temperature, humidity, and other relevant factors.
Do ask for paint manufacturers’ recommendations for coatings that minimize labor and reduce downtime.
Don’t overlook using equipment such as portable work platforms, spider staging, and air ducts for providing ventilation that can speed coatings application and drying.
Don’t specify coatings based on cost-per-gallon without considering coating application and performance advantages.
What is white metal?
A white metal blast-cleaned surface , when viewed without magnification, is free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products and other foreign matter, according to SSPC-SP5.