In sustaining facility roofs, cold-applied coatings are fundamental maintenance tools.  Before implementing a successful coating program, however, it is important to have a sound understanding of coating appropriateness, available coating materials and installation procedures.

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 radiation away from the roof membrane.
• 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 coated during installation, recoating normally is performed when the existing coating becomes deteriorated 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.
• Coatings can be used to upgrade a building's appearance where a particular roof is visible from the ground or adjacent buildings.
• 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 shouldn't be viewed as a substitute for replacement.  Although, coatings may restore the watertightness of a highly deteriorated roof in the short term, its costs may 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, coating should not be considered an economical roof management tool.

Second, ponded water usually reduces the service life of a coating.  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 where excessive dust, debris, steam, liquid discharge or other contaminants are present.  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 will likely develop in the first few years of coating's life.

Once project goals and criteria are defined, suitable coating products must be identified and specified.  Many products exist, but most can be classified as bituminous or elastomeric.

Bituminous coating products
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 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 may 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 ultraviolet radiation, reducing rooftop temperatures, premature aging and building cooling loads.  The quality of these products is measured by the aluminum content, expressed as 1 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 are 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 may contain reinforcing fibers.  These products serve many of the same functions as non-modified coatings, but increased elasticity, cold-weather flexibility and workability are advantages.  Increased cost is the primary disadvantage of many modified asphalt coatings.

Elastomeric coating products
Elastomeric coatings, as with bituminous coatings, encompass a wide variety of products.  They are formulated from latex/acrylic, Hypalon, neoprene, silicone, and urethane.  Many hybrid products exist, and new formulations are frequently introduced.  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 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.

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 may promote installation problems if the applicator isn't familiar with the application.

Product selection and applications
Selecting and specifying products requires that maintenance professionals 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 professional still should be involved.  The contractor should be required to submit product information sheets, the manufacturer's application requirements and limitations, and MSDS sheets.

The maintenance professional 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 professional can help ensure that surface preparation, application procedures and coverage rates match the specified requirements.

To maximize the owner's roofing investment, maintenance professionals should consider roof coatings for use in roof management programs.  For roof coatings to be valuable, the reasons for coating and feasibility must be evaluated.

If the decision is 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 help ensure a superior installation.