reaction to a solid state from the liquid form in which they are applied. 

 They include polysulfide, silicone, urethane, and epoxy-based materials. 

 The properties that make them suitable as sealants for a. wide range of uses 

 are their resistance to weathering and ozone, flexibility and resilience at 

 both high and low temperatures, and inertness to a wide range of chemicals, 

 including for some, solvents and fuels. In addition, the abrasion and 

 indentation resistance of urethane sealants is above average. Thermosetting, 

 chemically curing sealants have an expansion-compression range up to ±25 

 percent, depending on the one used, at temperatures from -40 to +82 

 Celsius (-40 to +180 Farenheit) . Silicone sealants remain flexible over 

 an even wider temperature range. They have a wide range of uses in buildings 

 and containers for both vertical and horizontal joints or in pavements. 

 Though initially more expensive thermosetting, chemically curing sealants 

 can stand greater movements than other field-molded sealants, and generally 

 have a much greater service life. 



(e) Thermosetting Solvent Release Sealants . Another class of 

 thermosetting sealants is the sealant which cures by the release of solvent. 

 Chlorosulfonated polyethylene and certain butyl and neoprene materials are 

 included in this class and their performance characteristics generally 

 resemble those of thermoplastic solvent-release materials. They are, 

 however, less sensitive to variations in temperature once they have "setup" 

 on exposure to the atmosphere. Their maximum extension-compression range 

 does not, however, exceed ±7 percent. They are mainly used as sealants for 

 calking and joints in buildings; both horizontal and vertical joints 



have small movements. The cost is somewhat less than that of other elasto- 

 meric sealants and the service life is likely to be satisfactory, though 

 for some recent products this has not yet been established by experience. 



(f) Rigid . Where special properties are required and movement 

 is negligible, certain rigid materials can be used as field-molded sealants 

 for joints and cracks. These include lead (cool or molten), sulfur, and 

 modified epoxy resins. 



f . Preformed Sealants . Preformed sealants (listed in Table 21) may be 

 divided into two classes: rigid and flexible. Most rigid preformed sealants 

 are metallic, such as metal waterstops and flashings. Flexible sealants are 

 usually made from natural or synthetic rubbers, polyvinyl chloride (often 

 called PVC) and like materials, and are used for waterstops, gaskets, and 

 miscellaneous sealing purposes. Preformed equivalents of certain materials, 

 e.g., rubber asphalts, usually categorized as field molded, are available as a 

 convenience to handling and installation. 



Compression seals should be included with the flexible group of pre- 

 formed sealants. However, because their functional principle is different, 

 and because the compartmentalized neoprene type can be used in almost all 

 joint sealant applications as an alternative to field-molded sealants, it 

 is treated separately. Preformed tension-compression seals are also 

 discussed separately. 



(1) Rigid Waterstops and Miscellaneous Seals . Rigid waterstops 

 are made of steel, copper and occasionally of lead. Steel waterstops are 

 primarily used in dams and other heavy construction projects. Because 

 ordinary steel may require additional protection against corrosion in dam 



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