Time and environmental conditions can take a toll on building exteriors, fading and degrading once-vibrant finishes. One option for restoration is to replace the façade with new, factory-fresh materials — a costly endeavor requiring major, disruptive construction. Another option is specifying a standard latex paint to restore the surface — a cost-effective, but short-term fix that can lead to ongoing maintenance and a compromised aesthetic. A third and better option is to specify section 09 96 00 high-performance field-applied coating systems for a long-term, cost-efficient and sustainable façade service life.
The right high-performance exterior coating can provide the same type of protection associated with factory-applied coatings. It also can provide aesthetic advantages when custom color-matched to align with branded or organizational color identities. For example, Solano Community College, located near San Francisco, recoated its Vallejo Center campus building with a custom-color NeverFade® with Kynar Aquatec® resin, a polyvinylidene fluoride (PVDF)-based, high-performance, restoration coating in a vibrant “Solano Blue” that identifies the college.
The specification process should consider several critical factors that can impact the effectiveness of the job well as the performance and longevity of the coating system.
Sunlight, moisture, temperature extremes, wind, particulate, chemical pollutants, and abrasion can drastically break down coating materials over time. Ultra-violet (UV) radiation is the most damaging of all environmental factors. Coupled with chemical agents, water and atmospheric pollution, these elements can react with a coating’s chemistry and pigment particles, attacking the chemical bonds of the coating’s binder resin.
The problem is more than just an aesthetic one. As coatings degrade and erode over time, they can take on a chalky consistency in which the coating is removed at even the lightest touch or rainfall. Eventually, the coating will continue to erode, removing the exterior material’s important protective layer and exposing the substrate. The result? Chalking, corrosion identified by rusting and pitting, mold/mildew growth and other problems that could lead to structural failure if not remedied.
Identifying challenging ambient conditions and choosing the appropriate polymer chemistry of the coating system is critical to prevent this degradation. Kynar Aquatec® resin, the backbone of NeverFade® Façade Restoration Coatings, is a PVDF technology comprised of carbon-fluorine atoms, which is one of the strongest chemical bonds that exists and is impervious to harsh UV conditions.
High-performance exterior coatings are specially formulated for compatibility with the surface or surfaces needing refinished. A formulation developed for stucco or masonry will likely not be compatible on steel or aluminum surfaces, for example.
The condition of the existing coating system will indicate whether complete removal or recoating is the best solution for surface preparation. The amount of corrosion or degradation present, degree of defects on the surface, the adhesion integrity, and type of existing coating on the substrate need to be considered before making an overcoat or complete removal decision.
Customer-centric high-performance coating manufacturers will assist with a pre-job inspection of the property and craft a project-specific CSI SectionFormat® specification for surface preparation and coating system application. They will also provide technical data sheets, safety data sheets (SDS) and field application guides, all of which should be consulted. These documents will provide important information about how to prepare the substrate and properly apply the coating system. Keep in mind, some projects and substrates may require more preparation than others.
In general, coatings should be tested on the substrate using ASTM D3359 Standard Test Method for Measuring Adhesion by Tape Test to verify that the coating has adhered properly to the surface.
COATING SYSTEMS: MORE THAN JUST PAINTING, IT’S ABOUT RESTORING
The vast majority of coating system failures can be traced to poor surface preparation. In the case of newly applied substrate materials like concrete, masonry and plaster, the substrate material should cure for at least 30 days before coating while monitoring the pH of the material — an important project timeline consideration. For steel, the degree and type of corrosion need to be evaluated and mitigated using proper SSPC or ISO standard practices for surface preparation prior to coating. Coatings isolate the substrate from the environment and form a barrier protection against corrosion. Applying the coating uniformly and properly is critical because a corrosion reaction can happen in an area smaller than a pinpoint.
A primer will provide an important bonding layer to help the topcoat adhere to the surface. Compatibility, or intercoat adhesion, between the primer and the topcoat is crucial; for this reason, it is not recommended to specify products from multiple manufacturers. Poor intercoat adhesion can lead to delamination, inadequate abrasion resistance, and other defects.
Selection of the right primer will depend on the substrate and the environment, discussed previously. Involving the high-performance coating manufacturer during the pre-job conference and inspection will help to eliminate incompatibility issues and specify the right system for the job.
Proper application techniques for the primer and topcoat must be followed in accordance with the coating manufacturer’s instructions. The coating system’s field application guide, product data sheets and specification will outline details such as coverage rates, dry time (to-touch and to re-coat), pot life, reduction instructions, as well as optimal ambient temperature and humidity conditions for application. Although it’s not always possible, application in direct sunlight should be avoided, as sunlight can affect the flow, leveling and application characteristics. High wind velocities can impact spray application, which can result in loss of materials, low film build, excessive dry spray or overspray. Be sure to work all these weather-related variables into the project timeline.
If the structure is normally exposed to dust and contaminants, the surface should be protected during the application and curing process. Dust and contaminants that settle on freshly applied coatings can impair the integrity of the coating, leading to a shorter coating life, possibility of surface defects and reduced performance.
The installation of a mock-up on a small portion of the structure prior to coating will allow for adhesion testing and ensure that the aesthetic and color meet the client’s expectations.
PVDF-BASED COATING SYSTEMS
When preparing a specification, there are several popular exterior coating systems to choose from, ranging from latex, epoxies, and polyurethanes, to high-performance polysiloxanes and FEVE-based options as well as hybrids of each. However, many in the architectural community have turned to high-performance PVDF, a tough engineering thermoplastic with a proven record of performance for over 50 years in extreme conditions. Its strong carbon-fluorine bonds allow the coating formulation to withstand thermal, chemical and ultraviolet conditions without degrading.
PVDF is innately hydrophobic and retains this property for an extended period. The hydrophobicity helps with water repellency and dirt resistance, by providing a low surface tension for a self-cleaning effect. While coatings with other types of polymeric resins may have some initial hydrophobic qualities, this characteristic tends to diminish after exposure to the elements for a year or two. PVDF also inherently resists mold and mildew growth, as there is no UV degradation or plasticizer migration creating a food source for bacterial growth. Because most PVDF-based coatings contain an acrylic component, fungicides are often incorporated to further resist mold growth, a prevalent problem in coastal areas or high humidity environments.
The polymer chains of the PVDF are not compromised by UV, unlike traditional latex or urethane coatings. However, when other polymers are incorporated, it’s important to look for coatings technologies with additional high-performance UV-blocking additives and complex inorganic pigments to protect the substrate from the harmful effects of UV rays. This ensures long-lasting fade resistance and a barrier of protection of the substrate below.
A LONGER LIFE
Incorporating section 09 96 00 into the specification, selecting a truly compatible coating system and a licensed applicator certified by that system’s manufacturer is a great start. An experienced and approved applicator’s expertise in selecting the right coating system to match the structure’s substrate, prepare the surface properly, perfect the application and maintain environmental compliance with local regulations will help ensure long-term success of the project. Look for a coating system that offers a long-life guarantee and a manufacturer that is involved in each step of the coating process.Read More...