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Restore Metal Roofing in the Field Using PVDF Latex Coatings

PHOTO CREDIT: ACRYMAX TECHNOLOGIES, INC.

Introduction

Metal is used extensively in architecture. For nearly 50 years, the coating technology chosen to protect exposed metal in architectural applications has been based on a fluoropolymer, namely polyvinylidene fluoride (PVDF). Coatings based on the PVDF resin technology exhibit outstanding weathering, color retention, and durability.

There are instances in which a building owner or facility manager may choose to recoat the exposed metal of their structure:

  • Cost – Recoating is cheaper than retrofitting, such as tear off and replacement of a metal roof
  • Color – A new owner may prefer a color change
  • New corporate identity – Color changes could be required to match a logo color or new corporate image

However, it is not possible to coat the metal with the original factory applied PVDF-based coating because a cure temperature of 450-500 degrees F. is required.

The alternative is a water based PVDF coating system that cures at ambient conditions and is designed to be applied in the field. The advantages of this system include:

  • Enhanced curb appeal – Due to the superior weathering performance of this technology, your exterior will look well-maintained through any precipitation.
  • Reduced maintenance costs – Needing fewer recoats and possessing strong mold, mildew, and dirt pickup resistance.
  • Environmental – Some formulations can have <100 grams/liter VOC, which is low compared to solvent systems.

In short, the expected performance of factory applied PVDF coatings is now available for field application, especially for metal restoration projects.

Building on PVDF Performance 

The main components of a coating are resin, pigment, solvent, and additives. In the case of water-based coating, water is the solvent. A highly weatherable coating must be formulated using a highly weatherable resin, such as PVDF, and highly weatherable pigments. 

Factory applied PVDF fluoropolymer resin-based coatings protect exposed metal and meet the highest performance standards for coatings on metal. These requirements are outlined in the AAMA 2605 standard. Factory applied PVDF-based coatings are used globally and are specified by architects because of their weathering and durability performance. This superior performance is achieved because the PVDF resin is transparent to UV light and therefore does not degrade like other resin technologies. 

Coatings formulated with the PVDF latex resin, another name for the water-based PVDF resin, can be applied in the field because these coatings will cure at ambient conditions. In addition to metal, coatings based on this technology can be applied to a wide variety of substrates, such as PVC, fiberglass, and fiber cement substrates, to enhance performance or extend the useful life of the structure. The performance of the PVDF latex-based coatings is similar to that of the factory applied PVDF system, namely its exceptional retention of gloss and color, and resistance to chalking, dirt pick-up, stains, mold, mildew and abrasion. 

Metal Restoration System

The PVDF latex is used in the top layer, or topcoat, of the system, and should be used as part of a three-step process to restore the metal substrate:

  • Surface preparation – Just like with any coating process, the surface must be properly prepared to be sound, clean, dry, and free of contamination.
  • Primer application – An acrylic primer is usually required, with a target dry film thickness of 2-10 mils.
  • Topcoat application – The latex PVDF-based coating is applied with a target dry film thickness of 2-6 mils.

The applicator should follow the topcoat manufacturer’s recommendation for primer selection and coating application. Conventional application methods, such as brush, roller, or commercial spray systems, can be used for both the primer and water-based PVDF latex topcoat. 

In addition, it is possible to formulate the latex PVDF-based topcoat using cool pigment technology. These are pigments, such as mixed metal oxides, that are extremely weather-resistant and reflect in the near infra red (IR) part of the spectrum. Sometimes, recoating the structure with a PVDF latex based coating with cool pigments can qualify the building owner for energy rebates. The Roof Coatings Manufacturers Association (RCMA) offers a database of current information on rebates and tax credits for installing reflective roofs as a benefit of membership with the association. 

Field application of PVDF latex based coatings is practical and economical for metal restoration applications when compared to replacement of metal components. Building owners and facility managers will realize the numerous, long established benefits of a factory applied PVDF coating in a field applied water-based PVDF system.

Charles Weidner is a Senior Business Development Engineer at Arkema Inc., contact him at: charles.weidner@arkema.com.

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