Coatings Complement Roof Systems

Cold Process Advantages

  Cold-applied products continue to be a very viable and necessary part of the contractor’s tool bag. They offer a number of advantages and complement the other product options available.

  Among those advantages are convenience. In general, there are minimal equipment requirements for the use of cold products. They are easy to store and deliver to the job site. Workmen can be readily trained in their application, and smaller crews can be used in certain job situations.

  Another advantage is that in many instances, there is little or no set-up time necessary with cold-applied products. They are ready to use out of the container. There is no need to premelt materials and crew time is not wasted while equipment is maintained or repaired. Equipment takedown also is minimized.

  A third advantage is safety. The hazards associated with hot-mopping and torching are eliminated for the crew, as well as for the building and its occupants. Coating and systems are available that are free of asbestos, odor and flammable solvents.

  Also, with cold-applied products, there is less mechanical sensitivity. The problem of overheating or underheating system components is removed. The crew has more time to work with its roofing materials because cool-down of bitumen is not a critical factor.

  Because they are water-based, emulsions can be applied over damp surfaces. This means morning dew or dampness from rain need not delay jobs. In addition, many coatings are self-priming, thereby eliminating this extra material and labor step.

  The final advantage is versatility. Cold products and systems are available for all types of roofing applications and weather conditions. They can be used in tight, restricted areas where other systems are impractical. They also can be used for maintenance, as well as for new, retrofit or replacement roofs.

Asbestos Substitutes

  The traditional primers, cutback coatings and cements, in both their tar and asphalt forms, have served the contractor long and well. What would a contractor do without a few drums of plastic cement for the countless number of roofing situations in which it is useful?

  The big change in these products is that many manufacturers have removed the asbestos fillers from them. The uniqueness of asbestos was not fully appreciated until the manufacturers began to seek suitable substitutes. Asbestos is primarily responsible for the weather-resistance and sag control, as well as for the film reinforcement of roof coating products. It accomplishes these tasks very efficiently and at a very reasonable cost. No single material was or has ever been found to provide this performance, even ignoring the cost factor.

  Studies had concluded that it was safe to use asbestos in a coating because it would be encapsulated. Unfortunately, public concern, insurance disadvantages, plant worker safety and governmental pressures all have combines to make it very difficult for a manufacturer to continue using asbestos as a raw material.

  In fact, the conversion to non-asbestos fillers has not been without difficulties from both economic and performance standpoints. The cost of the no-asbestos-filled products typically is higher, coating manufacturing procedures are more critical and there have been some field problems with the new materials as well.

  Nevertheless, some products that perform well are available asbestos-free. Furthermore, it is expected that prices will come down and performance will go up as coating manufacturers and raw material suppliers gain experience with the new technology.

  In the view of the author, public opinion eventually will eliminate the use of asbestos in all roofing applications. This judicious contractor is best advised to convert to asbestos-free products now, even though there may be some economic penalty.

  Because of the reduced reliance on asbestos as a raw material, a greater portion of the performance load must be carried b the other coating ingredients. Specifically, this means that great care must be taken by the manufacturer when choosing asphalt.

  The source of crude, extent of distillation of the crude residues and the degree of blowing all combine to determine the weathering and performance of an asphalt.

  Other properties of the asphalt determine its acceptance of filler, the amount of solvent required for proper application viscosity, storage stability and a number of other performance parameters taken for granted by the applicator.

  This means that selection of asphalt is more critical than it ever has ben before. Only roofing products with demonstrably acceptable performance should be used from dependable suppliers.

Rubberized Coatings

Roofs are dynamic assemblies. Factors such as building stress, roof traffic, temperature changes, wind forces and a variety of other factors combine to create constant movement within a roof.

  Whereas the predominant measure of roof performance has been tensile strength, we now are heading terms such as work-to-break, strain energy and load-elongation curves. Simply put, it has been recognized that materials with greater extension capabilities, rather than pure strength, offer superior long-term performance in many roofing applications.

 To this end, manufacturers offer roof coatings and mastics which are modified with any of a number of available elastomerics. The types commonly employed are butyl, SBS and neoprene, although others may be used.

  These materials offer substantially higher elongation values, in the range of 700 percent to 1,000 percent at room temperature, with greatly improved cold temperature flexibility. The rubberized mastics are especially useful at flashing joints, where they tie in elastomeric membranes, or at any other points on the roof where high movement is expected.

  Many times these highly flexible coatings and mastics are used in conjunction with polyester reinforcements, creating a composite with good flexibility and fatigue resistance.

Resaturants

It is not the purpose of this article to take a position pro or con on the effectiveness of resaturants. The debate in the usefulness of these materials has been long and hard, and there have been few, if any, converts to either side.

  Much of the controversy has resulted from exaggerated claims on the part of some of the promoters of this type of coating product. Among the advantages of resaturants that can be objectively demonstrated is that they lower the softening point of the bitumen top pour of a built-up roof by infusing oils into the aged asphalt or tar.

  They also restore water-resistance and flexibility to exposed, dry felt, add additional waterproofing to the surface of the roof and provide a means of attaching new gravel.

  Many in the industry take the position that one of the greatest advantages of the use of resaturants is that they require the owner to inspect his built-up roofing system and address any problems before they become uncorrectable.

  Resaturants, like other bitumen-based coatings, have ben reformulated to remove the asbestos filler. Asbestos removal has been less critical with this class of product because resaturants typically use only small amounts of filler. By nature, their non-sag requirements are much less severe than cements or other types of coatings.

  Another development involving resaturants is the availability of water-based products or emulsions. These products are said to be ecologically clean and odor-free while still performing the same functions as their solvent-based equivalents.

  Although introduced as a proprietary system, these products are being offered by more and more manufacturers. They have proven very useful in situations in which there is a high sensitivity to odor during application, such as at schools and hospitals.

Advances in Emulsions

Emulsions simply are very small droplets of asphalt in a continuous phase of water. There are two general types of asphalt emulsions in common use-chemical and clay.

  The difference between the two is the method of stabilization used to keep the asphalt particles from coming together, called agglomerating, and settling to the bottom of the container during storage.

  The first type uses chemicals or soaps, and their stabilization chemistry depends on the same general principle as when dirt or grease is emulsified or washed off your hands.

  The second type uses a unique plate-like clay material known as bentonite, which orients itself where the asphalt and water interface and places the same electrical charge on all the asphalt particles. The asphalt droplets now repel each other, just as two magnets do when their poles are oriented plus-to-plus and minus-to-minus.

  Clay-stabilized emulsions are the preferred type for roofing applications for a variety of reasons. The first is that the clay forms a honeycombed network as the film forms and the water evaporates from the coating. This network keeps the film static and allows the use of clay emulsions on any slope, including a vertical one.

  A second advantage of clay-stabilized emulsions is that they have excellent weathering characteristics. The clay protects or screens the asphalt particles from ultraviolet rays, and weathering takes place by chalking or slow erosion rather than drying out, as with cutbacks.

  Although these emulsions do not require a protective covering, weathering and longevity can be improved by using highly reflective aluminum or light-colored paints and coatings.

  Another advantage is that the clay particle network provides good fire-resistance properties. In spread-of-flame testing, the flow of material into the fire source can result in a failure to pass the test.

  But the static nature of the clay emulsions retards this flow, and many times it allows an assembly to be fire-rated which otherwise would not pass. Modified bitumen suppliers have used this technique to their advantage in obtaining fire approvals.

  Both clay and chemical emulsions can be applied over damp surfaces, as long as they are not wet or ponded. This gives the contractor greater flexibility and latitude in planning his work.

  The disadvantages of emulsions are that they must be kept from freezing and they might wash off if rain occurs after application.

New Emulsions

With increasing consciousness of health and safety, as well as growing governmental regulation, emulsions and water-based products are becoming more popular. Coating manufacturers are therefore devoting additional efforts to the development of unique and higher-performing asphalt emulsions.

  The work primarily has been along two lines. The first is to improve the coatings’ wash-off resistance by causing the emulsion to break or cure at a faster rate after application.

  The second is to use polymer or rubber additives in the base asphalt emulsion to increase its flexibility and elongation properties. In some cases, the addition of polymer additives accomplished both goals of accelerating the cure and improving final film properties.

  The objective of rapid cure has been accomplished mostly through the use of two-part systems that are applied in a co-spray technique. These products are formulated using chemical asphalt emulsions to which a latex rubber (usually neoprene) has been added.

  This rubber latex and asphalt emulsion blend is delivered to the job as component A. Component B is a water solution of a metal salt which reacts with the stabilizing chemicals of component A, causing an immediate cure.

  Components A and B are applied simultaneously onto the roof surface using a double nozzle spray head. The rubberized asphalt film is formed instantaneously, and the water carrier literally pours off the roof and down the drains.

  Two of the problems that have slowed acceptance of this technology are the tendency for blister formation if the substrate to which this system is applied, such as exposed organic felts, absorbs moisture. The second problem is the sensitivity of the application equipment and a difficulty in obtaining uniform, reproducible delivery of the correct amounts of components A and B. nevertheless, this type of system is being used with success in Europe and in some parts of the United States.

  Other methods of accelerating cure are by the use of polymer additives, which can decrease the time to achieve wash-off resistance in half, and by spraying a protective film onto the emulsion after it has been applied. The second of these options is cumbersome and costly, and it has not made much progress in the marketplace.

  To better accommodate the movement that takes place in every roofing system, greater emphasis has been places on the development of emulsions with elastomeric qualities. Manufacturers have employed a number of polymer modifiers, including neoprene, acrylics, and SBS.

  All these materials show improved tensile and elongation properties, as well as improved low-temperature roof performance. But spraying these materials sometimes is more difficult because the gun tips clog.

Fire-retardant Coatings

Fire-resistive coatings have found only limited applications in roofing. Because of their relatively high cost, they are employed only when there is no other reasonable alternative.

  For example, the use of sufficient gravel generally will ensure an acceptable fire rating at a relatively low cost. When either roof slope or weight considerations exclude gravel s an option, manufacturers and specifiers must consider use of granules or some coating option.

  As mentioned before, clay-based asphalt emulsions show fire-resistive properties because of the matrix set up by the bentonite. Many of the fire ratings for modified bitumens include an emulsion surfacing with a coating of a reflective paint.

  Some of the modified bitumen and elastoplastic sheet manufacturers have chosen to incorporate fire-retardant materials directly into the membrane to avoid the extra step of applying a surface coat.

  Suppliers of EPDM sheet membranes also have relied on the use of chlorosulfinated polyethylene (CSPE or Hypalon) coatings in which sand is embedded to reach competitive fire ratings. In this case, the sand is the key to the attainment of the rating. The Hypalon coating, although contributing to the fire resistivity, serves as a means of adhering the sand to the EPDM sheet’s surface.

  Manufacturers of the more exotic fire-resistant coatings, such as intumescents (which swell to form a firm char) have not enjoyed much success in the roofing market. Coatings of this type would have to be sold for $25 per gallon or more with coverage rates of at least 2 gallons per square.

Cold-applied Membranes

Through the years, coatings manufacturers have become increasingly involved in the development of membrane systems. The earliest cold process membranes were based on coated organic felts applied in three- or four-ply configurations with an asphaltic-based interplay adhesive. The same adhesive also served as the top coat for adhering granules or gravel.

  Eventually, the suppliers of these systems turned to the use of coated glass felts along with the rest of the industry. These systems have strong market penetration in some parts of the country, especially in the Western states.

  More recently, with the availability of suitable polyester materials for roofing, a number of coatings suppliers also have introduced systems based on these new synthetic reinforcing materials. The better of these systems use either one or two coated base sheets in combination with plies of uncoated polyesters.

  The advantages of these new systems offer parallel those of the polyesters. They have superior elongation and recovery, better work-to-break or strain energy, good flexibility and fatigue resistance and a high puncture and tear resistance.

  Another general classification of cold membrane systems uses an acrylic latex coating in combination with either glass or polyester reinforcing materials. Because the key raw material for these coatings is produced by a large chemical company, a significant number of local and regional marketers and manufacturers of these systems have appeared.

  The advantages of these materials are that they are water-based, odor-free and white in color, so they have no need for a reflective topcoat. Other advantages include the availability of the back-up research of a large technical organization and the elastomeric properties of the cured coating.

  Other problems are that because the products are relatively easy to supply, they may be marketed by companies inexperienced in roofing applications. Another disadvantage is that performance is marginal in ponded roof areas, and adhesion is not properly prepared.

  There also is some activity in the areas of solvent-based and two-part (high solid) elastomeric roof membranes. Although some inroads have been made, high cost and the lack of concerted marketing efforts have slowed the acceptance of these materials. The sources of many of these products are European countries that do not have established marketing bases in the United States.

Application Techniques

The application of cold-applied membrane systems, although not difficult, requires the use of techniques that differ from traditional procedures.

  For example, the coated glass systems require that the ply sheets be cut into 15-foot to 20-foot lengths and allowed to relax for at least 30 minutes prior to installation. If this is not done, so-called memory ridging takes place a day or two after installation and must be repaired.

  In working with cold systems, it must be remembered that the properties of the system develop over a period of time. The instant set of hot systems does not occur. Cold membrane installations are more weather-sensitive.

  If the system is water-based, rain and cold will cause problems with wash-off or lack of cure. If the system is solvent-based, wash-off still may be a problem.

  Also, residual stresses in the membrane components will have time to release before set or cure takes place. This stress release may result in an uneven surface appearance, although the membrane performance is unaffected.

Conclusion

The future trends of roofing in the United States are difficult to predict. But it is clear that coatings always will maintain an important part of the market.

  Coating manufacturers are working hard to maintain market presence and identify coating needs in the application and maintenance of modified bitumen and elastoplastic membranes.

  The ultimate goal of coatings suppliers is to identify and design a membrane system that will compete effectively with the membranes that dominate the market today. 

Originally published in Contractors Guide, August 1988