Roof Coating Considerations

Long-term coatings performance starts with attention to application and maintenance issues during specification

By Tom Irvine  

In sustaining facility roofs, cold-applied coatings are fundamental maintenance tools. Before implementing a successful coatings program, however, it is important that maintenance and engineering managers have a sound understanding of coating appropriateness, available coating materials and installation procedures. A closer look at each of these components helps ensure the coating and the roof deliver intended long-term performance.

Coating Appropriateness

Six situations exist that are considered appropriate roof-coating applications.

  • The most basic reason is to extend or maximize roof service life by reflecting harmful ultraviolet (UV) radiation away from the roof membrane.
  • Coatings can be used effectively in conjunction with roof repairs to restore a moderately aged roof to a maintainable watertight condition.
  • If a roof had been coated during installation, recoating normally is performed when the existing coating deteriorates and no longer protects the underlying membrane.
  • Reflective or light-colored coatings can minimize solar gain and, as a result, reduce a building’s cooling loads.
  • Managers also can specify coatings to upgrade a building’s appearance where a particular roof is visible from the ground or from an adjacent building.
  • Certain UL-classified coatings can increase a roof’s flame spread resistance. This type of application typically is specified in conjunction with roof system construction. Flame spread resistance, however, can be upgraded after a roof is in service.

At least three situations exist, however, in which coating application is not usually considered a good investment.

First, applying a coating never makes a bad roof good and should not be viewed as a substitute for replacement. Although coatings can restore the watertightness of a highly deteriorated roof in the short term, its costs can represent 10-15 percent of the cost of a new 20-year old roof system. Generally, if the design life of the coating is greater than the estimated remaining serviceable life of the coated roof membrane, managers should not consider coatings to be an economical roof management tool.

Second, ponded water usually reduces a coating’s service life. If standing water remains 48 hours after a rain shower, problems such as material degradation, loss of adhesion and flaking can result.

Third, coatings are susceptible to problems in environments with excessive dust, debris, steam, liquid discharge or other contaminants. One key to coatings application is proper preparation of the substrate to be coated. If contaminants can’t be completely removed, poor adhesion, flaking or other deficiencies are likely to develop in the first few years of coating’s life.

Types of Coatings

Once managers have defined project goals and criteria, the next step is to identify and specify suitable coating products. Many products exist, and most can be classified as bituminous or elastomeric.

Bituminous coatings. Many bituminous coatings exist, but the majority are:

  • emulsions
  • aluminums
  • emulsion-aluminums
  • asphalt cutbacks
  • resaturants
  • modified asphalt coatings.

Bituminous coatings generally are compatible with asphalt or coal-tar built-up roofs or with modified bitumen membranes. Some manufacturers, however, market these coatings for metal-roof restoration.

Emulsion coatings consist of asphalt dispersed in a colloidal clay-water blend and are dark gray, brown or black. Emulsions generally function as protective or maintenance coatings for asphalt built-up or modified bitumen roofs, and they generally increase the roof’s fire resistance.

Aluminum coatings are a mixture of oxidized asphalt, solvents and aluminum paste, and they are available with or without reinforcing fibers. Aluminum coatings reflect UV radiation, reducing rooftop temperatures, premature aging and building cooling loads. The quality of these products is measured by the aluminum content, expressed as 1/2, 2, or 3 pounds of aluminum paste per gallon.

Aluminum paste properties vary greatly. Premium products contain 60 percent or more aluminum per pound of paste; many commodity products contain 45 percent or less within the same quantity of paste. The higher the aluminum content, the longer the coating will last.

Emulsion-aluminum coatings are hybrid products providing with the fire resistance and filling/sealing properties of an emulsion coating. For restoration, they reduce the costs associated with practice of applying an emulsion coating, followed by a reflective surfacing coat.

Asphalt cutbacks can be made with or without reinforcing fibers. They consist of asphalt and petroleum solvents. Cutbacks are primarily maintenance and restoration products, designed to penetrate, resaturate and restore weathered or aged asphalt built-up roof systems.

Resaturants, made with either an asphalt or coal-tar base, are available fibered or nonfibered and are a combination of bitumen--asphalt or coal-tar--and compatible solvents. These coatings also function as maintenance and restoration materials to penetrate, rejuvenate and weatherproof existing built-up roofs.

Modified asphalt coatings are made with asphalt, synthetic rubber polymers and solvents and might contain reinforcing fibers. These products serve many of the same functions as non-modified coatings, but their advantages include increased elasticity, cold-weather flexibility and workability. Increased cost is the primary disadvantage of many modified asphalt coatings.

Elastomeric coatings. As with bituminous coatings, elastomeric coatings encompass a variety of products. They are formulated from:

  • latex/acrylic
  • Hypalon
  • neoprene
  • silicone
  • urethane.

Many hybrid products exist, and new formulations are introduced frequently. Many elastomeric coatings are compatible with most common roof membranes, but they are more widely used with metal and sprayed-in-place polyurethane foam roofing systems.

Latex/acrylic coatings are water-based products and enjoy the largest share of the elastomeric market. These coatings comply with increasingly stringent solvent emission regulations and represent a lower cost alternative to other polymers.

Hypalon coatings generally are used to restore surfaces of single-ply membranes. They offer good waterproofing properties and excellent resistance to chemicals, ultraviolet radiation and fire.

Neoprene coatings are composed of synthetic rubber polymers, are black and offer excellent elongation and recovery properties. Neoprene coatings are used as a base coat beneath Hypalon coatings in some multi-coat applications.

Silicone and urethane coatings are available in one- or two-component products. These coatings generally are more expensive than other elastomeric coatings, but they offer additional benefits, including enhanced resistance to chemical fallout, ponding water, heat, ultraviolet radiation and roof traffic.

Single-component products can be easier to use than two-component materials. With the latter, rigid mixing requirements, limited pot life or prepared material and other product-specific factors can promote installation problems if the applicator is not familiar with the application.

Selection and Specification

Selecting and specifying products requires that maintenance managers become familiar with the products offered, their advantages and disadvantages, and most importantly, their ability to meet the criteria identified.

A qualified roofing professional can offer help be reviewing project criteria, inspecting the roof and recommending products. Products under consideration should have a history of successful applications on roofs with similar criteria. Also, manufacturers’ representatives should provide a tour of nearby successful applications. They also should provide recommendations for specific preparation and application procedures, qualified applicators, etc.

After applicators have bid the coating work and authorization to proceed is awarded, the maintenance manager still should be involved. The contractor should be required to submit product information sheets, the manufacturer’s application requirements and limitations, and material safety data sheets.

Managers also can hold a preconstruction meeting with the contractor and manufacturer’s technical representative to review project specific requirements.

During application, quality control by the maintenance manager can help ensure that surface preparation, application procedures and coverage rates match the specified requirements.

To maximize the organization’s roofing investment, maintenance managers should consider roof coatings for use in roof management programs. But for roof coatings to be truly valuable, managers will have to evaluate the reasons for coating and the coatings’ feasibility.

If the decision is to proceed with the application, managers will have to identify project criteria and appropriate products. After a professional applicator is selected, product submittals, a preconstruction meeting, quality control and involvement by a representative of the coating manufacturer can help ensure a superior installation.

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  posted on 7/1/2002   Article Use Policy

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