Sealant selection, joint design

The term primer is used to describe any liquid preparation used to modify the surface of an adherend. While there are some primerless systems, the sealants used in construction often require primers as the surface condition may be extremely variable (See Sealant joint design, Seaiants in doubie giazing and Selection of joint sealants). 

Performance of primers has been studied both in general construction and water-retaining structures.Further information may be found in articles on Selection of joint sealants. Sealant joint design, Paint primers and Primers for adhesive bonding. 

When calculating the design width of joints in a building, it is essential to take account of the tolerances on the relevant dimensions of the components and the accuracy in placing them that is likely to be achieved on site. For these reasons, there may, in practice, be considerable variation in the widths of a number of ostensibly identical joints. The joint width for the design must ensure that in no joint will the sealant be subjected to a level of compression or extension that, when expressed as a proportion of the achieved joint width, exceeds its movement capability. (See the Selection of joint sealants, where Table 1 gives maximum movement permitted for each major type of sealant.) However, considerable variation in formulation and properties may occur between different brands of the same chemical type, which may affect this value. The maximum tolerable joint movement quoted by the manufacturer should be used in joint design calculations. 

The following is a description of the selection of the appropriate sealant, then proper joint design and installation for construction sealant/ caulk applications. 

Proper design of sealant joints is critical to the reliability of the joints. The general types of sealant joints and the critical geometric parameters that must be considered in joint design will be discussed in detail. Because the proper selection of materials is absolutely critical to the reliability of sealant joints, the critical sealant properties will also be discussed. 

As already stated, the durability or permanence of a bonded assembly is dependent on the intended use and service conditions to which the bond will be exposed. However, the joint design, choice of substrates, adhesive selection, substrate preparation, and primer selection, where appropriate, plus the method of application and assembly all have significant impact on the service life of adhesively bonded materials. Most or all of these considerations are interdependent, for example, the joint design and substrates chosen will limit the range of suitable adhesives that can be employed. In a similar way, the durability of a sealed joint is only as good as the adhesion of the sealant (and primer) to the surfaces forming the joint. Primers and/or sealants will adhere to surfaces only if those surfaces are properly prepared. A very large proportion of all sealant joint failures result from poor or inadequate surface preparation. 

Epoxy adhesives and sealants are generally not significantly affected by simple outdoor weathering. However, there are certain circumstances that could affect the permanence of joints exposed to outdoor service, ft is important that these be considered early in the design of the adhesive joint and selection of materials. 

The selection of an alloy for a specific application is based on the cost and the corrosion resistance of the alloy in the environment of interest. It is also possible to subject the chosen alloy to a process by which the corrosion resistance of the selected material can be improved within the acceptable limits. Some of the corrosion prevention and protection strategies with respect to the aluminum-based alloys are (i) design (ii) alloy selection and joint sealants (iii) aluminum thermal spraying anodic coatings (iv) inhibitors (v) conversion and organic coatings and (vi) cathodic protection. 

A preliminary article indicates the scope and types of Sealants. In designing a sealant joint, it is essential to select a snitable sealant with adequate capability to withstand the expected movement at the joint... 

Several chapters are devoted to the Materials to be bonded (metals, plastics, wood, composites). These chapters explain the important properties of adhesives and sealants used for these materials, the method of designing the joints, selecting the adapted adhesives and sealants, and also provide many practical examples of bonding in all industries,... 

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