14.1 Introduction

This chapter will review the necessary steps that must be taken to provide the proper sealing system for specific applications. Whereas the previous chapter gave descriptions of the various materials that are commonly used as sealants, this chapter will provide guidance for both the selection of the sealant and the proper methodology for joint design and application.

The design of a sealing system involves more than merely choosing a material with the right physical and chemical properties. The following considerations are also essential to obtain optimal performance:

1. Joint design, including back-up or bedding materials

2. Type and nature of the substrates

3. Application, curing, and performance characteristics of the sealant

In this chapter, we will first try to understand the requirements imposed by the design of the joint and by the substrates, and then we will try to define the application and performance considerations that are necessary for selecting the proper sealant.

As with adhesives, a well developed methodology is necessary in the design of sealing systems because there is no ideal sealant. If there were an ideal sealant, it would be one that would stick to any unprimed substrate, yet would easily squeeze out of the caulking gun and flow into the joint. It would become tack-free quickly to minimize dust pickup, and it would cure quickly to become impervious to the environment. The ideal sealant would form smooth beads that are easily cleaned. It would shrink little on curing, and once cured, it would remain plastic and rubbery...