Which of the following is a disadvantage of certain sealant backers?

Certain sealant backers can undergo chemical reactions when they come into contact with specific types of sealants, which can compromise the integrity and performance of the sealant system. This reaction can lead to poor adhesion, degradation of the sealant, and ultimately, failure of the joint if not properly addressed. Sealant backers must be compatible with the materials used to ensure that they perform effectively in their intended application, making this consideration crucial in the selection process for glazing projects.

The other options, while they may pose concerns in different contexts, do not directly relate to the inherent performance characteristics and compatibility issues that can arise from chemical reactions. For instance, increased cost or limited availability may be factors in material selection but do not impact the operational effectiveness of the sealant itself. Similarly, excessive flexibility during application might affect the ease of installation but wouldn't necessarily lead to the same critical problems posed by chemical compatibility.