Jointing Compounds and Sealants

Corrosion prevention compounds (CPCs) are fluids that can both prevent new corrosion sites from forming (Fig. 14.6) and, more importantly, suppress any corrosion that has initiated. CPCs are 

The water displacing CPCs act by spreading across surfaces, into cracks and crevices where they displace any moisture present, leaving behind a residue to act as a further barrier after the carrier solvent has evaporated. The hard film CPCs dry to a waxy or hard resin-like finish after application and provide a barrier film to corrosive environments. 

CPCs have been used by the aircraft industry for many years as a means of protecting against corrosion. These treatments are often 

These products are also extensively used on road vehicles to reduce the severity of corrosion, particularly in cold-weather areas as roadways are coated with salt mixtures to break down snow and ice. There are plenty of locations in road vehicles where water can accumulate and rust form to cause premature failm e of the equipment or perforation of the sheet metal. The imderside of cars is especially vulnerable to rust and corrosion due to the exposme to high levels of moisture. 

Thin fluid film CPCs are typically used on road vehicles as a yearly maintenance application for added corrosion protection. The CPC treatment using air powered spray units is relatively inexpensive and can be provided by various rust-proofing centers (Fig. 14.8). 

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Test Method for Tack Free Time of Caulking Compounds and Sealants Specification for Nonbituminous Inserts for Contraction Joints in Portland Cement Concrete Airfield Pavements, Sawable Type Specification for Joint Sealant, Hot Poured, Elastomeric Type, for Portland Cement Concrete Pavements... 

Muscovite Mica 6915,6912,6908,6905 - grades of different particles sizes for plastics and coatings SG-70, SG-90 - hydrous potassium aluminum silicate produced by patented process which gives high brightness delaminated muscovite mica for joint compounds, adhesives, sealants, coatings... 

Test for determination of water absorption by sealant backup (joint filler) material Practice for laboratories engaged in the testing of building sealants Test for slump of caulking compounds and sealants Test for staining of caulking compounds and sealants... 

Caulks and sealants are compounds designed to fill and seal relatively large joints, cracks and depressions. They not only improve appearance, but also protect against intrusion of water and weather [100]. Hastomeric behaviour is required to conform to joint movement, and high solids content fcnmulations are preferred to minimize shrinkage and stress upon drying. Acrylic latexes of moderately low... 

Hot Melt, Field-Extruded Sealants. Several butyl raw material manufacturers and sealant producers have recently developed butyl tapes. These are premasticated, high viscosity thermoplastic compositions that are fed as talced ribbons into a polymeric sealant applicator (PSA). Within the PSA, the compound is heated and extruded into the joint opening to form a smooth joint that cools rapidly with excellent adhesion claimed, even to oily or otherwise poorly prepared surfaces. These hot-applied, post-formed butyl tapes have been successfully used to seal insulated glass units, automotive windshields (Fig. 4), curtain walls, concrete pipes, precast concrete structural joints, and as bedding compounds in combi-... 

Urethane sealants have good elongation and recovery, excellent abrasion resistance and tear strength their resistance to indentation make them the preferred compounds for floor joint compounds, highway and airfield joint materials, and preformed gasket seals in clay and concrete pipe. Low temperature performance (to below —40°C) is superior to that of the... 

There are various uses requiring compounds with different flow characteristics. These range from a self-leveling material and one that must resist flow completely in vertical joints. A balance between fine and coarse fillers achieves the desired flow characteristics. Fine particle fillers build a network that result in thixotropic behavior. This must be balanced by the desired consistency and cost of the finished sealant. Care must be taken that the fillers are adequately dispersed to achieve the desired thixotropy. Specifically designed additives are available to impart thixotropy to a polysulfide sealant. These are listed in Table XI. 

Besides durability, premium sealants are judged by special properties as shown in Table 4. The ability to take on greater elongation and compression is measured by movement capability in terms of joint width. The stability to UV exposure is important for those glazing and insulation compounds used in modern high-rise structures. Thermal stability is in demand for solar collectors, or for other structural materials. On the basis of these evaluations, we can foresee future trends of sealants as shown in Table 4. Silicones appear to out-perform others. In the meantime, technical advances will provide low-modulus polysulfides, and better movement ability for both polysulfides and polyurethanes. Their cure time will be decreased and the UV stability will be improved to match or compete with silicones. All three will be developed for better adhesion under the un-primed conditions. 

Intermediate movement accommodating sealants include solvent-based and emulsion-type acrylic systems, higher quality butyl/PIB blends, neoprene and styrene-butadiene (SBR) based compounds. These have sufficient movement tolerance to be used in joints subject to both settlement and thermally induced movement across the sealant. These intermediate type systems cure by means of solvent evaporation with some auto-oxidation, or a mixture of the two processes. 

Most of these systems use the one-shot technique and are based on MDI with either a polyether or a polyester. Crude or polymeric MDI or other liquid variants of MDI predominate. Formulations usually contain high catalyst concentrations of either tin or mercury salts to give a very rapid cure at room temperature within a few minutes. It is usual to use additives to provide specific properties of density and lower the cost. Applications are commercial vehicle floor mats, cable jointing and potting compounds, sealants, moulds and the like. 

Hot-applied polymeric sealants are formulated with a carefully balanced blend of polymer with certain compounds, like asphalt, plasticisers and inert reinforcing fillers to produce a hot-pour point sealant with excellent bonding properties, high resiliency, ductility and resistance to degradation from weathering, to provide a positive seal during expansion and contraction of the joint. 

Test for adhesion and cohesion of elastomeric joint sealants under cyclic movement Test for extrudability after package aging of latex sealing compounds Test for aging effects of artificial weathering on latex sealing compounds Test for volume shrinkage of latex sealant compounds... 

Talc applications include caulking compounds, sealants, auto putties, mastics, and joint compoimds based on polybutene, polyisoprene, butyl rubber, polyurethane, and polyvinyl acrylate. 

Butt joints (a) simpie thin-substrate butt Joint, (b) simple thick-substrate butt Joint (c) compound butt Joint (d) seaiant bead seai, and (e) sealant tape seal... 

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