What classification identifies sealants that can withstand a joint width variation of +/- 25%?

The classification that identifies sealants capable of withstanding a joint width variation of +/- 25% is indeed Class 25. This classification is part of the American Society for Testing and Materials (ASTM) standards for sealants, particularly ASTM C920, which provides requirements for various types of sealants used in construction.

Class 25 signifies that a sealant can accommodate significant movement in a joint, making it suitable for applications where there are fluctuations in temperature, building movement, or other environmental conditions that could cause joint size to vary significantly. Sealants rated in this class are designed to maintain their adhesive and cohesive properties under these conditions, thus ensuring long-lasting performance in joints that experience a higher degree of movement.

Other classifications, while they serve specific purposes and have their own movement capabilities, do not match the +/- 25% variation that Class 25 can accommodate. For instance, Class 12 1/2 allows for less movement than Class 25, and other standards, such as Type S and Grade NS, focus on different performance characteristics entirely, such as specific usage scenarios rather than joint movement capabilities.