The manufacturing process differentiates these uncured elastomeric membranes from vulcanized polymers. During the production of vul-canized polymers, combinations of chemicals, primarily polymers, fillers, and additives, are processed together and cured by heating so that chains of molecules are permanently crosslinked.
This curing method results in a thermoset membrane with low ten-sile strength and high elongation values. In the field, cured elastomers must be applied and repaired with adhesives. New chemical bonds cannot be formed.
Nonvulcanized, uncured elastomers, in contrast, are manufactured without any crosslinks between chains of polymer molecules. Although
exposure to the elements can naturally cure some of these polymers during their lifespan, all nonvulcanized elastomers can be heat-welded during the initial installation.
The generic classification of polymers known as nonvulcanized elastomers includes chlorosulfoned polyethylene (CSPE), chlorinated polyethylene (CPE), polyisobutylene (PIB), and nitrile alloy with butadiene-acrylonitrile copolymers (NBP).
CHLOROSULFONED POLYETHYLENE (CSPE)
CSPE, sold under the DuPont trademark Hypalon, is a polymer that has enjoyed increased popularity over the years because of its attrac-tive white appearance and energy-efficient, heat-reflecattrac-tive properties.
Other factors contributing to the popularity of CSPE and other rubber-based, single-ply roofing systems include
■ Long-term weatherability; excellent resistance to temperature extremes, sunlight, ozone, and moisture
■ Ease, speed, and cleanliness of installation
■ Reduced labor costs in many cases
■ Flexural stability; accommodation of deck movement and dis-placement
■ Routine reroof installation over existing moisture-free mem-branes
■ Compatibility with many insulation materials
■ Code and standardization progress by the RMA and others
■ Ease of maintenance
■ Proven long-term performance
Another benefit is adaptability. Application techniques allow rubber-based roofing systems to be applied to virtually any roof sur-face: flat, spherical, curved, or slanted.
CSPE is a saturated polymer that contains chlorine and sulfonyl chloride groups attached to a polyethylene backbone. It is an elas-tomeric material. Typical elongations range from 200 to 400 percent, depending on the type and amount of reinforcing fillers present in the SINGLE-PLY ROOFING
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compound. This means that CSPE can stretch far beyond its original length and return to its original configuration without loss of struc-tural integrity.
Actually, a unique feature of CSPE is that it is manufactured as a thermoplastic, but over time it cures as a thermoset. This means that most CSPE systems are typically hot-air- or solvent-welded. The advantages of welded seams include relatively quick procedures, good strength, and the lack of additional seaming material. There are two primary methods of application for CSPE rubber-based, single-ply sys-tems, each of which offers certain advantages in specific applications.
Mechanically fastened. The membrane is loosely laid over the sub-strate and then anchored to the deck using fasteners. Many types of mechanically fastened systems are available. The most common are those that attach directly to the deck. Nonpenetrating systems also are available. Advantages include the fact that the systems are lightweight, easy to install, and relatively inexpensive.
Fully adhered. Ideal for contoured roofs or sloped surfaces that can-not withstand the weight of a ballasted system, fully adhered mem-branes are completely bonded to the substrate with contact adhesives. The major advantages include the fact that these sys-tems are lightweight, durable, and easy to maintain. They also have an aesthetically clean and smooth appearance.
Only a handful of CSPE systems are installed using the ballasted technique popular with other rubber-based roofing systems because most building owners prefer not to cover the attractive white mem-brane. In fact, CSPE systems are often specified because of their attrac-tive white exterior.
CHLORINATED POLYETHYLENE (CPE)
This material is formulated around its prime polymers and blended with pigment and processing aids, which serve as release agents and antioxidants. In fact, one manufacturer produces 15 grades of cured and uncured raw CPE polymer.
CPE made its roofing debut in 1967. Prior to that, it emerged in var-ious military and civilian applications, most notably as a pond liner.
The majority of today’s CPE roof membranes are offered in an uncured composition and are reinforced with a polyester scrim by individual roofing manufacturers. Standard thicknesses are 40 to 48 mils. Both CPE and CSPE normally are formulated without plasticizers because of their inherent flexibility as an elastomer.
As closely related elastomers, CSPE and CPE share similar behav-ioral characteristics. An aged CSPE, however, cannot be heat-welded.
Adhesives must be applied if field repairs are necessary. The methods of application are the same for CPE and CSPE.
POLYISOBUTYLENE (PIB)
PIB is usually a 60-mil membrane made from synthetic rubber poly-mer, or polyisobutylene, pigments, fillers, and processing aids within several quality-control parameters that relate to thickness, density, elongation, hardness, and so on. The underside of the mem-brane is generally laminated with a 40-mil, needle-punched, non-woven, rot-proof polyester fabric. The membrane is finished with a 2-inch-wide, self-sealing edge material that is protected by a strip of release paper.
PIB is compatible with hot asphalt and shows excellent resistance to weathering, radiant heat, and ultraviolet (UV) light. Used primarily as a final waterproofing membrane over existing flat or low-sloped roof assemblies, PIB can also be used as a waterproofing membrane for new-construction roof assemblies.
PIB is a lightweight system that requires no ballast. It can be installed quickly and economically. PIB passes UL’s Class A fire rating and FM’s I-90 wind-resistance rating.
These systems offer both the building owner and the roofing con-tractor numerous advantages. The self-sealing edge offers assured seam strength, long-term waterproofing, lower installation costs, faster application per worker hour, and no need for special capital equip-ment. The fact that the system is unballasted can eliminate the need to structurally reinforce the building before it is reroofed. PIB also mini-mizes the deck load and eliminates the logistics of adding 1000 to 1200 pounds of gravel for every 10-foot-square area.
PIB has a short but successful history in the United States. As more people become familiar with the system, realize that it is a solution for SINGLE-PLY ROOFING
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many roofing problems, and view the evidence of product support and longevity, the PIB system continues to show steady growth in the sin-gle-ply market.
NITRILE ALLOYS (NBP)
These membranes, as thermoset elastometers, are compounded from butadiene-acrylonitrile copolymers, nonvolatile polymeric plasticiz-ers, and other patented ingredients.
These membranes typically are made by coating the compound on a heavy-duty polyester fabric. They range in thickness from 30 to 40 mils. Seams are hot-air welded. Used for almost 30 years for such diverse products as exterior door gaskets and footwear, NPB is recog-nized for its weather-protectant and waterproofing capabilities. The material exhibits good chemical resistance and low-temperature flexi-bility, but is sensitive to aromatic hydrocarbons.