When you see a sealant labeled as "ASTM C920 Class 25," it is referring to a specific coding system. Understanding this code tells you exactly how the sealant will perform.
| Property | Test Method | Requirement Example | | :--- | :--- | :--- | | | C679 | ≤ 72 hours | | Hardness | C661 (Shore A) | 15–60 | | Tensile adhesion | C719 (Cyclic movement) | No cohesive failure after 500 cycles at temperature extremes | | Extrusion rate | C1183 | Consistent flow through a nozzle | | Staining | C510 | No staining of porous substrates | | Artificial weathering | C1442 | Retain ≥75% of original elongation | | Low-temperature flexibility | C734 | No cracking at -40°F (-40°C) | astm c 920