construction stainless steels are used to overcome this. They must be low 

 in carbon and stabilized with columhium or titanium to facilitate welding 

 and retain corrosion resistance after welding. Although annealing is 

 required for improved flexibility, the stiffness of steel waterstops may 

 still lead to cracking in the adjacent concrete. 



Copper waterstops are used in dams and general construction. They are 

 highly resistant to corrosion, but must be handled with care to avoid 

 damage. For this reason, and because of cost, flexible waterstops are 

 often used instead. Copper is also used for flashings. 



Use of lead as waterstops, flashings, or protection in industrial 

 floor joints is now very limited. Bronze strips find wide application in 

 dividing, rather than sealing, terrazzo and other floor toppings into 

 smaller panels. 



(2) Flexible Waterstops . The types of materials suitable and in 

 use as flexible waterstops are shown in Table 21. Butyl, neoprene, and 

 natural rubbers have good extensibility and resistance to water or chemicals 

 and may be formulated to give good recovery and fatigue resistance. PVC 

 compounds are, however, probably now the most widely used. While it is 



not quite as elastic as the rubbers, recovers more slowly from deformation, 

 and is susceptible to degradation by oils, grades with sufficient flexi- 

 bility (especially important at low temperatures) can be formulated. PVC 

 has the great advantage of being thermoplastic and hence it can easily be 

 spliced on the job or special configurations made for joint intersections. 

 Flexible waterstops are widely used as the primary sealing system in water- 

 containing projects such as dams, tanks, monolithic pipelines, floodwalls, 

 and swimming pools, to keep the water in, and in buildings below grade or 

 in earth-retaining walls to keep the water out. 



(3) Gaskets and Miscellaneous Seals . Gaskets and tapes are 

 widely used sealants between glazed surfaces, around windows and other 

 openings in buildings, and at joints between metal or precast concrete 

 panels in curtain walls. Gaskets are also extensively used at joints 

 between precast pipes and where mechanical joints are needed in service 

 lines. The sealing action is obtained either because the sealant is com- 

 pressed between the joint faces (gaskets) or because the surface of the 

 sealant, as in the case of polyisobutylene, is pressure-sensitive and thus 

 adheres. 



(4) Compression Seals . These are preformed compartmentalized or 

 cellular elastomeric devices which, when in compression between the joint 

 faces, function as sealants. 



(a) Compartmental i zed . Neoprene extruded to the required 

 configuration is currently used for most compression seals. The neoprene 

 formulation used must have special properties for this application. To 

 effectively seal, sufficient contact pressure must be maintained at the 

 joint face. This requires that the seal be in some degree of compression 

 and, for this, good resistance to compression set (i.e., the material must 

 recover sufficiently when released) is required. In addition, the neoprene 

 must be crystallization-resistant at low temperatures (the resultant 

 stiffening may make the seal temporarily ineffective though recovery will 



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