Glass Fiber Reinforced vs. Glass Flake Reinforced Coatings for Water and Wastewater Infrastructure

Glass Flake Reinforced Coatings 

The History of Glass Flake Reinforced Coatings 

The use of glass flake in coatings is not new, it has been around since 1959. The coatings of 1959 are not as evolved as today, these coatings were simply applied by trowel or brush and were used to reinforce roof light panels made from polyester resin. Over time it was found that the roof panels would distort when exposed to ultraviolet (UV) light. This led to extensive coatings research and during the 1960’s research began investigating its use in organic coatings. By the mid 1970’s development of a spray-applied glass flake coating evolved; however, due to a lack of available application equipment, the coating was thought to be exotic, unstable, difficult to apply and expensive. It took until the 1980’s for it to become a readily available and acceptable coating to be applied.

Benefits of Glass Flake Reinforced Coatings 

The coatings are formulated using synthetic glass that is consistent in composition and clear in color using “C” glass. “C” glass is a good glass for additives that need to be resistant to chemical corrosion. It is often used in environments that are acid corrosive. The use of “C” glass provides the following benefits:

• High levels of chemical resistance
• Chemically inert (not chemically reactive)
• Good mechanical properties
• Non-hazardous, just simple mechanical dust hazards

Manufacturing Techniques for Glass Flake Reinforced Coatings 

The flakes created using “C” glass vary in thickness and plate size and are manufactured using two different techniques, bubble or spun method. The bubble method is the cost-effective method when comparing the two. The reason being is it has a high throughput production rate, it is produced using pre-melted glass marbles, resulting in a curved flake.

The spun method is more expensive to produce, approximately by 30%, but produces a flat, non-curved thinner flake (as low as 100nm with deviation of +/- 25nm). The thinner the glass flake the greater number of flake layers formed, further reducing permeability, the state or quality of a material or membrane that causes it to allow liquids or gasses to pass through it. The greater the number of flake layers formed, the longer the path is for moisture vapor or contaminants to penetrate through.

Resins for Glass Flake Reinforced Coatings 

Once the glass flake is manufactured, a resin needs to be selected to serve as the binder and create a coating. The resin is selected based off the commodity, environment, mechanical properties and chemical resistance needed. Resins that can be used are:

• Polyesters
• Epoxies
• Chlorinated rubbers
• Alkyds
• Coal tars
• Vinyls
• Waterbased acrylics

Corrosion Resistant Characteristics of Glass Flake Reinforced Coatings 

As stated above, glass flake is used as an additive in protective coatings to prevent corrosion. Glass flake has the following corrosion resistant characteristics:

• Low thickness to surface area
• Platelet form
• Particles of high aspect ratio
• Improved chemical resistance due to its inert composition
• Reduction in cathodic disbondment (the breakdown of adhesion between a coating and the coated substrate to which it is applied)
• Increased impact and abrasion resistance
• Increased thixotropic characteristics
• Increase hardness

Low Thickness to Surface Area

Once a glass flake thickness is chosen, it is important to optimize particle size and addition level. Addition level depends on the type of resin, surfactants, bubble release agent and other pigments or fillers being used. The typical flake content added to resins ranges from 10-50% by weight of the coating. The larger the glass flake size, the greater reduction in permeability.

Coupling or bonding agents, a compound which provides a chemical bond between two dissimilar materials, are used to provide better adhesion of the glass flake to the resin and the substrate. A common coupling or bonding agent used is silane. The pre-treated flake will permit a much higher level of glass flake added to resin, improve the bonding performance, and increase tensile and flexural strength, the resistance of a material to breaking under tension and the material’s ability to resist deformation under load and vapor permeability.

Lamellar Platelet Form

Glass flake is in the form of a lamellar platelet, meaning it is flat and disc and non-spherical. This allows the pigment to lay flat and overlap one another, extending and creating a tortuous path length for passage of moisture or gas diffusion.

Particles of High Aspect Ratio 

High aspect ratio fillers, such as glass flake, have a high ratio of the length of the filler to its cross-sectional diameter. The higher the aspect ratio, the greater the barrier protection provided. However, care must be taken when selecting glass flake, as out of alignment, large aspect ratio flakes will cause a direct path through the coating where the coating is less in thickness than the nominal diameter of the glass flake. When this happens, you run the risk of the following:

• Crack propagation
• Decrease in flexibility and elongation
• Rough surface finishes

An additional benefit of using particles of high aspect ratio is the ability to improve fire retardancy. As described above, the thin glass flake platelets overlap within the coating film, creating a lengthened tortuous path providing an oxygen barrier in the fire-retardant system. Overall, reducing smoke emissions, improving polymerization shrinkage rates, heat distortion and creep.

Increased Thixotropic Characteristics 

Thixotropic coatings are a coating that changes its viscosity in different states. In the initial state, the coating is thick, but it becomes thinner and easy to apply when it is mixed actively, allowing for increased film builds per coat. By increasing the single coat thickness, the owner engages in cost savings through the elimination of the number of coats that are needed to be applied, eliminating variables such as adhesion issues between coats due to contamination, amine blushing of the primer or intermediate coat and recoat window concerns.

Glass Fiber Reinforced Coatings 

The History of Glass Fiber Reinforced Coatings 

The history of fiber reinforced coatings began with experimenting with glass fiber. Glass wool, or better known as fiberglass, was invented between 1932 and 1933. The main use was for thermal building insulation and as a reinforcing agent for many polymer products.

Types of Glass Used to Produce Glass Fiber Reinforced Coatings 

There are different types of glass to produce glass fiber. The type of glass is selected on what the glass fiber is needed for. The chart explains the types of glass and the reason for selection.

Types of Glass Fibers Used to Produce Glass Fiber Reinforced Coatings

There are two types of glass fibers, isotropic and anisotropic. Isotropic refers to the properties of a material which is independent of the direction, whereas anisotropic is direction-dependent. This means anisotropic glass fibers have a different value for physical properties when measured in different directions, creating the following limitations:

• Strong in tension and compression along its axis
• Weak shear strength
• If a collection of glass fibers is arranged permanently in a preferred direction within a coating, then the coating may be preferentially strong in that direction
• Acts as a thermal insulator because of high ratio of surface area to weight, but increased surface area makes the coating more susceptible to chemical attack

Thermosetting Polymers for Glass Fiber Reinforced Coatings 

A coating is formed by combining the glass fibers with a thermoset polymer. Typical thermosetting polymers are:

• Epoxy
• Polyester resin
• Vinyl ester
• A thermoplastic

Challenges and Disadvantages of Glass Fiber Reinforced Coatings 

An issue of concern during the curing process is the amount of contraction that occurs of the resin. For example, polyesters contract between 5-6% whereas epoxies contracts approximately 2%. Glass fibers do not contract; therefore, creating changes in the shape. Distortions can appear hours, days or weeks after the resin has cured. While this distortion can be minimized by symmetric use of the fibers in design, a certain amount of internal stress is created; and if it becomes too great, cracks will form.

When using glass fiber, the level of corrosion prevention is limited, a lot of this contributed to the shape of the fiber. Glass fiber are strands and do not overlap in the way lamellar platelets do, making the path to the substrate quicker and easier than with glass flake, offering only limited resistance to water and gas diffusion through the coating film.

Glass fiber can be added into a coating as an inert additive or as a laminate system, combining two or more substrates (concrete or steel to glass fiber mat) together by bonding them together (resin serves as bonding agent). Overall application cost may be higher when applying as a laminate due to it requiring additional application steps. After the glass fiber is placed into the resin, it is permitted to cure. Often, sanding of the glass fiber strands is required to create a flush surface and then is followed by neat resin placed over top to avoid wicking of the fiber (fiber absorbing elements in its environment). These extra steps add to the overall costs of additional labor, time and materials to the project.

Case Study: Enhancing Wastewater Infrastructure Projects with Glass Flake Reinforced Coatings 

Note: Below information can be found at Applicator Boosts Asset Lining Productivity | Sherwin-Williams

Situation: Leveraging Glass Flake Reinforced Coatings for Wastewater Infrastructure 

Based in Douglasville, Georgia, the Douglasville-Douglas County WSA was enhancing its Southside Lift Station by adding bar screen equipment before the station to remove rags and debris. The project included adding an 8-foot diameter by 18-foot deep manhole and two other manholes that were 4-feet and 18-feet deep. AIRCO lined the concrete structures using Dura-Plate 6000. The 100% solids, high-build glass flake reinforced epoxy lining allowed AIRCO to rapidly coat the assets using single-leg spraying, while also enabling the WSA to have those assets ready for service less than half a day following the lining applications. These efficiencies helped to accelerate the project schedule and reduce labor costs.

Execution: Efficient Application of Glass Flake Reinforced Coatings in Wastewater Systems 

After the manholes were installed and mortared, AIRCO pressure-washed the concrete at 5,000 psi to ensure a good profile before spray-applying the Dura-Plate 6000 glass flake reinforced epoxy lining system using single-leg equipment. Applicators sprayed the glass flake-filled coating at a 120-mil wet film thickness (WFT) in a single pass directly to the prepared concrete. The product hung very well at this high film build, which was specified to help mitigate the corrosive effects of the severe wastewater service the assets will encounter.

The single-leg spraying capabilities provided an easier, more cost-effective installation for AIRCO compared to when spraying other fiber or microfiber filled products with plural-component equipment. Most high-solids epoxy lining formulations require the use of plural-component spraying equipment, which is bulky and hard to maneuver around job sites. Higher skilled—and more expensive—applicators are also required to operate the equipment, which can raise project costs. However, despite being a 100% solids, high-build coating, Dura-Plate 6000 can be applied using single-leg spraying equipment, which improved efficiencies and profitability for AIRCO, while also lowering costs for the owner.

“Single-leg spraying is much more feasible than just running a pump down there to spray the coating,” said Joe Wainscott, Vice President of AIRCO. “Now that we have this capability, we can get in and out a lot faster and complete more assets per day.”

Based on the Dura-Plate 6000 lining’s 10-hour return to service time, asset owners can also realize productivity gains. Single-leg products typically require a day or more to cure before allowing returns to service. Dura-Plate 6000’s shorter curing time helps asset owners significantly reduce downtime and its associated costs by returning assets to service sooner.

“Anytime you don’t have to deal with plural-component equipment, but you can get a fast return to service, that’s a big deal,” said Wainscott.

Asset longevity is also a big deal, and Dura-Plate 6000 delivers on this need. The product’s glass-flake reinforced epoxy formulation provides low permeability to mitigate the effects of corrosive media attacking concrete and steel substrates below the lining material. This makes the lining system suitable for severe wastewater immersion and headspace environments, sewer collection systems, wastewater treatment plants and other challenging environments.

Outcome: Boosting Productivity and Profitability in Wastewater Infrastructure Projects with Glass Flake Reinforced Coatings 

AIRCO’s switch to applying Dura-Plate 6000 glass flake reinforced epoxy linings via single-leg spraying has improved efficiencies and profitability for the applicator – far beyond what it first realized on the Douglasville-Douglas County WSA project. While AIRCO sprayed the WSA’s assets by hand, the applicator has realized even further productivity strides by switching to applying the product using a single-leg spincaster.

“We doubled our productivity when we first transitioned to this product and were able to move from plural-component spraying to single-leg spraying. We have perhaps doubled our productivity again, if not more, after we moved to slinging the coating,” said Wainscott.

For asset owners like the Douglasville-Douglas County WSA, the enhanced application productivity of Dura-Plate 6000 combined with accelerated return to service times is also enhancing efficiencies in their operations.

Transform Your Water and Wastewater Infrastructure Projects with Glass Flake Reinforced Coatings from Sherwin-Williams 

When comparing glass flake to glass fiber, glass flake offers significant upgraded performance, increasing life cycle and reducing overall cost when protecting our water infrastructure from premature corrosion. The use of glass flake creates a barrier to be formed due to its diffusion morphology of being lamellar platelets, decreasing the overall risk of contamination from moisture and gas. The lamellar platelet’s structure creates an extensive permeation path length making it a tortuous path to the substrate. In addition, due to the structure and method of incorporating into the resin, the number of coats required are minimized, reducing overall labor costs while improving life cycle of the coating.

If you’re looking for high-quality glass flake reinforced coatings, contact Sherwin-Williams today. Our team is ready to help you find the right products for your water and wastewater infrastructure projects, ensuring you get the best solutions for long-lasting protection and performance.