Historically, cold-applied roof coatings and cements have proven to be effective and economical in solving the challenges associated with the installation of new roofing, as well as in the preventive maintenance and repair of existing roof surfaces. The following discussion is designed to present general information about roof coatings, their manufacture, and proper application. Overview Cold-applied roof coatings and cements have been successfully used for well over 50 years, gaining both recognition and market share. Ancient Beginnings The use of cold-process coatings dates back to at least 3000 BC, when Egyptians began using varnishes and enamels made of beeswax, gelatin, and clay. Later they used protective coatings of pitch and balsam to waterproof their wooden boats. Around 1000 BC, the Egyptians created varnishes from gum arabic. Independently, Asian cultures developed the use of lacquers and varnishes, and by the 2nd century BC, were using them as coverings on a variety of buildings, artwork, and furnishings in China, Japan, and Korea. The Early Greeks and Romans also relied on paints and varnishes, adding colors to these coatings and applying them on homes, ships, and artwork. In addition, most of the earliest recorded dwellings in Europe, Asia, and the Americas used various cold-applied mixtures of clay, soil, and water, as well as stucco pastes of water, sand, and limestone or gypsum to waterproof their roofs and walls. In Babylon, the surface of mud walls was made waterproof with “mineral pitch” brought from the river. Many of these early coating materials are still used in the coatings of today. Historical Advances The development of more sophisticated protective coatings appears to have begun in the latter half of the 17th century, when a German chemist found a way to use the stickiness of coal tar as a protective coating on woods and ropes. During the 19th and early 20th centuries, scientists developed a variety of new organic, inorganic, and synthetic materials for use in coatings, binders, and solvents. Perhaps the most dramatic advance in coating properties has come in the past 40 years with the development of polymers. 10 • Interface September 2004 A researcher applies a coating on a test panel in ongoing research by RCMA. Cold-applied Roofing Systems During the middle of the 19th century, a new type of roofing was created by soaking rag felt in tar (pine tar or coal tar), layering these felts with moppings of hot tar, and covering the assembly with gravel. The tar was eventually (mostly) replaced by asphalt, as was the rag felt with fiberglass mat to create the modern built-up roof (BUR). For the better part of a century, if a low-slope roof was called for, the hot-applied built-up roof was the only choice. In the middle part of the 20th century, as roof coatings became more popular, someone discovered that cold-applied roof coatings could be used to adhere the plies of roofing felt, and the use of hot asphalt and roofing kettles could be avoided. The first cold-applied membrane roofing system was invented. Roofing technology has evolved rapidly since then, and there are dozens of different materials that can be used to create a roof today. Cold-applied roofing systems have advanced in step and are more popular today than ever. Types of Cold-applied Roofing Systems The term “cold-applied roofing system” is traditionally taken to mean a built-up roofing system assembled using solvent-borne bituminous (liquid) adhesives and multiple plies of reinforcement. There are, however, several other types of roof membrane systems on the market (single-ply, spray foam, etc.) that do not require heating, so it is necessary to be more specific. The specific types of coldapplied roofing are listed below. 1. Cold Process Built-up Roofing System This type of roof can now be constructed a variety of ways. The predominant technique is to use heavyweight asphalt coating fiberglass “base” sheets and bond them with solvent-borne asphalt adhesives in multiple plies. The first sheet is usually mechanically attached to the substrate (insulation) and subsequent plies (usually three or four total) are embedded in an application of adhesive at a rate typically between 1.5 and 2.5 gallons per square (100 sq. ft.). The membrane is then covered with an aggregate surface or roof coating. Cold process built-up roofing systems now exist that use coated or uncoated polyester reinforcements, or composite (polyester/fiberglass) reinforcements, in conjunction with either solvent-borne or waterborne adhesives. The combination of reinforcement and adhesive is typically proprietary to the system provider and compatibility should be verified with the manufacturer. Cold process built-up roofing systems are available as complete systems or as repair system for new construction or re-roofing, and Application of a polymeric base coat. (Copyright Tremco Inc.) September 2004 Interface • 11 Laying out gravel. (Copyright Tremco Inc.) they are available in a variety of constructions to meet all budgets. Roofs rated by Underwriters Laboratories (UL) and Factory Mutual (FM) are now available. 2. Adhesive Application of Modified Bitumen Modified bitumen roofing is similar to built-up roofing in that it employs reinforcing materials coated with bitumen. The primary difference is the use of “modification” or addition of polymers to the bitumen to achieve improved characteristics. Like built-up roofing, modified bitumen roofs were typically installed using moppings of hot asphalt. An alternate approach for some types of modified bitumen was to use a propane torch to melt the back of the sheet, creating a molten adhesive in which the roll could then be embedded. Perhaps the fastest growing segment of coldprocess roofing is the application of modified bitumen roofing in bituminous cold-process adhesives. For obvious safety reasons, use of cold-applied roofing has provided an attractive alternative to the use of hot asphalt or open flame. These roofs typically have a mechanically attached base sheet, and one or two plies of modified bitumen membrane installed in bituminous adhesives. 3. Liquid-applied Monolithic Membrane Systems A third type of cold-applied roof now exists that blurs the line between roof coating and roof membrane system. That is the liquid-applied monolithic roof system. Typically made of high-tech polymeric resins such as urethanes or bitumens that have been modified with polymers such as SEBS, these roofs are applied as a liquid and may not rely on reinforcing material, but cure to form a tough, rubber-like membrane. These types of roofs are monolithic (no seams) and are typically considered self-flashing. What are Cold-applied Roof Coatings and Cements? Cold-applied coatings and cements are those designed to be used at ambient temperatures, requiring little, if any, heating to facilitate application. Typically, they are comprised of a resin, a carrier solvent, reinforcing fillers, and optional reflective pigments. Upon application, the carrier solvent evaporates from the coating, leaving a cured, water-resistant film. Formulation Options Roof coatings and cements are available with a wide range of properties and consistencies to fit a multitude of purposes. Lowviscosity, non-fibered coatings are formulated as penetrating primers and damp-proofing coatings. Medium-viscosity, fibered, and nonfibered coatings and cements are formulated as interply adhesives and top coatings for use on commercial, industrial, and residential roofs. Some of these coatings incorporate pigments (aluminum, titanium dioxide, and others) to reflect the damaging rays of the sun, creating a longer performing and more energy-efficient roof. High-viscosity, heavybodied cements are designed for adhering waterproofing membranes and components and for patching and repairing leaks. Product Advantages The primary advantages of roof coatings and cements are their economical, proven performance life, and ease of use. Roof coatings and cements are generally one-component products that can be applied directly from the container. Today’s coating and cements Laying out base sheet in cold adhesive for a modified bitumen roof system. (Copyright Tremco Inc.) Hot mopping over insulation for a conventional built-up roof system. (Copyright Tremco Inc.) 12 • Interface September 2004 September 2004 Interface • 13 are versatile and applicator friendly. Non-flammable products are also available. Bituminous Roof Coatings and Cements Traditional bituminous roof coatings and cements are made from “cutback” bitumen. Distillate bitumen residue is further refined to various specific properties through vacuum distillation or oxidization. This refined bitumen is then blended with a petroleum solvent, such as mineral spirits, to make the cutback bitumen. This blend of bituminous resin and solvent is further combined in various type mixing or dispersing vessels with special clay fillers, surfactants, fibers, or fillers to create a gelled coating. Reflective aluminum pigments may also be incorporated into the mixture to formulate a coating that provides protection against the damaging effect of the sun’s rays. The proportions of each of these components ultimately determine the consistency and properties of the coating or cement. Polymeric Roof Coatings and Cements Coatings and cements can also be formulated with a variety of synthetic resins such as acrylic, Neoprene, styrene butadiene, urethane, polyvinyl acetate, and others. The enhanced performance properties achieved by using these resins include, but are not limited to: low temperature flexibility, chemical resistance, and elasticity. Like bituminous coatings, polymeric coatings can be either solvent- or water-borne. In addition, they can also incorporate fibers, fillers, clays, and pigments to achieve the desired consistencies and properties. Polymer Modified Roof Coatings and Cements These coatings and cements are a hybrid of the previously discussed groups. They are manufactured by combining polymeric technology with bitumen technology. The resultant coating or cement exhibits an economical blend of performance properties and characteristics. These coatings and cements are also available in solvent- and water-borne versions, with a selection of consistencies and properties. Roof coatings, in all their various forms – bituminous (asphalt or coal-tar) and non-bituminous (acrylic or elastomeric); brush, spray, or trowel grade; petroleum solvent or water thinned; furnished in cans, pails, drums, or tank wagons – are all quality products that are easy to use and economical. ■ Joseph Hobson is director of communications and member services for both the Roof Coatings Manufacturers Association (RCMA) and the Asphalt Roofing Manufacturers Association (ARMA). He has also previously served as director of communications for the Cool Roof Rating Council and the National Coalition of Petroleum Dry Cleaners, and general manager of the National Association of Legal Search Consultants. ABOUT THE AUTHOR JOSEPH HOBSON And so does the real value of a roof. The way we see it, the real cost of a roof is calculated over 20 to 25 years. (Of course, it helps if you start with a FiberTite® roof that can actually last that long.) Do the math. Or, call 800-927-8578 ext.1335 to let one of our professionals demonstrate our life cycle cost calculator. trustfibertite.com Sometimes, real beauty takes time to be seen.
