ROOF COATINGS

by Tom Irvine

ROOF COATINGS: An Examination of Coating Appropriateness, Project Criteria, Available Products, and the Installation Process

In sustaining facility roofs, cold-applied coatings are fundamental maintenance tools available to facility management professionals. Before a successful coating program may be implemented, it is important to have a general understanding of coating appropriateness, individual project criteria, available coating materials, and installation procedures.

APPROPRIATENESS OF ROOF COATING APPLICATION

There are six situations that are considered prudent applications for roof coatings.

• Perhaps the most basic reason for coating a roof is to extend and/or maximize roof service life by reflecting harmful ultraviolet radiation away from the roof membrane. Another positive benefit is a general slowing of the aging process by reducing day to day membrane temperatures.
• Coatings may be effectively used in conjunction with roof repairs to restore a moderately aged roof to a maintainable watertight condition.
• If a roof was originally coated during installation, recoating is normally performed when the existing coating becomes deteriorated and no longer protects the underlying membrane. This procedure is normally required within 5 years after roof installation.
• Reflective or light colored coatings can be applied to reduce a building's cooling loads by minimizing solar gain.
• Coatings can be used to upgrade a building's aesthetic value, where a particular roof is visible from the ground or adjacent buildings.
• Increasing a roof's flame spread resistance can be achieved by the use of U. L. Classified coating products. This type of application is typically specified in conjunction with roof system construction. However, flame spread resistance may be upgraded after the roof has been in service.

Conversely, there are a least three situations where coating application is not normally considered a good investment.

• Application of a coating will never make a bad roof good, and should not be construed as a substitute for replacement of a deteriorated and leaky roof. Although coatings may restore the watertightness of a highly deteriorated roof over the short term, the cost for performance of the coating work may represent 10-15 percent of the cost of a new 20-year roof system. As a general rule, if the design life of the coating is greater than the estimated remaining serviceable life of the (coated) roof membrane, coating should not be considered an economical roof management tool.
• With some exceptions, ponding water will reduce the longevity of a coating application. If notable standing water remains 48 hours after a rain shower, problems will likely be experienced in the form of material degradation, loss of adhesion, flaking, or crazing.
• Coatings are also susceptible to accelerated deterioration in certain industrial environments where excessive dust, debris, steam, liquid discharge, or other contaminants are present. One of the keys to coating application is proper preparation of the substrate to be coated (similar to painting). If contaminants can not be completely removed, poor adhesion, flaking, or other deficiencies will likely develop in the first few years of coating's life.

IDENTIFICATION OF PROJECT CRITERIA

When the decision is made to proceed with a roof coating project, project criteria and objectives must be identified for each individual roof planned for coating or recoating. Is the key objective to restore service life and decrease roof maintenance costs, or is aesthetics the only considerations? Is the building's usage being changed such that increased fire resistance is required by the local building code. Has the Owner purchased a building that requires roof restoration work? What type of roof system is present or proposed? The coating must be compatible with the type of membrane to be coated. What type of rooftop environment is present? Is chemical discharge, high foot traffic, or ponding water an issue? What is the project budget? The answers to these and any other applicable questions will define the project criteria.

Once the criteria are identified, suitable coating products must be identified and specified for the application. A myriad of products exist, but most may be classified as either bituminous or elastomeric coatings.

BITUMINOUS COATING PRODUCTS

Many bituminous coatings exist, but the majority are either emulsions, aluminums, emulsion-aluminums, asphalt cutbacks, resaturants, or modified asphalt coatings. Bituminous coatings are generally manufactured to be compatible with asphalt or coal-tar built-up roofs, or modified bitumen membranes. However, some manufacturers market bituminous coatings for metal roof restoration.

Emulsion coatings consist of asphalt dispersed in a colloidal clay-water blend, and are dark gray, brown or black in color. Emulsions generally function as protective or maintenance coatings for asphalt built-up or modified bitumen roofs, and may be fire resistant. Aluminum coatings are a mixture of oxidized asphalt, solvents, and aluminum paste, and are available with or without reinforcing fibers. Aluminum coatings function to reflect ultraviolet radiation, thus reducing rooftop temperatures, premature aging, and building cooling loads. The quality of aluminum coating products are measured by the aluminum content; typically expressed as 1-1/2, 2, or 3 pounds of aluminum paste per gallon. It is important to note that aluminum paste properties vary greatly from manufacturer to manufacturer. The premium products contain 60 percent or more aluminum within each pound of paste. Many commodity products contain 45 percent or less within the same quantity of paste. Generally the higher the aluminum content, the more brilliant and long-lasting the coating will be. Emulsion-aluminum coatings are hybrid products providing the reflectibility of an aluminum coating with the fire resistance and filling/sealing properties of an emulsion coating. For restoration projects, this product reduces the costs associated with the common practice of applying an emulsion coating, followed by a reflective surfacing coat. Cutbacks are manufactured with or without reinforcing fibers, and consist of asphalt and petroleum solvents. Cutbacks are primarily maintenance and restoration products, designed to penetrate, resaturate, and restore weathered or aged bituminous built-up roof systems. Resaturants are manufactured 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/restoration materials to penetrate, rejuvenate, and weatherproof existing built-up roofs. Modified asphalt coatings are manufactured with asphalt, synthetic rubber polymers, solvents, and with or without reinforcing fibers. These products serve many of the same functions as the non-modified coatings, but increased elasticity, cold weather flexibility, and workability are all advantages. Increased cost is the primary disadvantage of modified asphalt coatings.

ELASTOMERIC COATING PRODUCTS

As with bituminous coatings, elastomeric coatings encompass a wide variety of specialty products. Elastomeric coatings are formulated from latex/acrylic, Hypalon, neoprene, silicone, and/or urethane. Hybrid products exist, and new formulations are always being introduced into the market. Elastomeric coatings are compatible with most common roof membranes, but 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 coating market. These coatings comply with the increasingly stringent solvent emission regulations, and represent a lower cost alternative as compared to other polymers. White is most widely used, although many alternative colors are available. Hypalon coatings are generally utilized to restore the surfaces of single-ply membranes, and have the advantages of good waterproofing/sealing properties, and excellent resistance to chemicals, ultraviolet radiation, and fire. As with the acrylic coatings, white is the most popular, but many other colors are available. Neoprene coatings are composed of synthetic rubber polymers, are black in color, and offer excellent elongation and recovery properties. Neoprene coatings are utilized as a base coat beneath Hypalon coatings in some multi-coat applications. Silicone and urethane coatings are available in either single or two-component products. These coatings are generally more expensive than other elastomeric coatings, but offer additional benefits such as enhanced resistance to chemical fallout, ponding water, heat, ultraviolet radiation, and roof traffic. The single-component products are generally more user friendly, when compared with the two-component materials. With the latter, non-forgiving mixing ratios, limited pot life of prepared material, and other product specific factors may promote installation shortcomings if the applicator is not completely familiar with the product application requirements.

PRODUCT SELECTION AND APPLICATION

Selecting and specifying products will require that the maintenance professional become familiar with the basic products offered, their advantages and disadvantages, and most importantly, their ability to meet the criteria identified for the roof under consideration. A qualified roofing professional can offer assistance by inspecting the roof, and recommending suitable products that meet the project requirements. Products under consideration should have a history of successful applications on roofs with similar criteria to the proposed project. Manufacturer's representatives should provide a tour of nearby successful applications. Recommendations for specific preparation/application procedures, qualified applicators, etc., could also be provided by the manufacturer's representative.

After qualified applicators have bid the coating work and authorization to proceed is awarded, additional procedures may be required to ensure the project's success. Submittals should be required of the contractor, including product information sheets, the manufacturer's published application requirements/limitations, MSDS sheets, and any other pertinent information. Conducting a preconstruction meeting with the contractor and manufacturer's technical representative to review project specific requirements may prove beneficial. During application, quality control by the maintenance professional would be beneficial to ensure that surface preparation, application procedures, coverage rates, etc., are in accordance with the specified requirements. The manufacturer's technical representative should be called upon to assist with this facet of the project as well.

CONCLUSIONS

To maximize the Owner's roofing investment, maintenance professionals should consider roof coatings for inclusion in their roof management programs. The first steps in developing an effective coating program are to determine the reasons for coating and evaluate each projects feasibility. If the decision is made to proceed, project criteria and appropriate products must be identified. After a conscientious and professional applicator is selected, product submittals, a preconstruction meeting, quality control, and involvement by a representative of the coating manufacturer will expedite a superior installation.

Biography

Tom Irvine has been a Roof Consultant with Benchmark, Inc., Cedar Rapids, Iowa (formerly Taylor Associates, Inc.), since 1991. Benchmark offers professional roof consulting and project management services to commercial, institutional, and industrial clients on a national basis.