Astm C920 Class 25 Vs Class 50 Upd Jun 2026

for large glass panels, high-rise building facades, or any structure in a climate with extreme temperature swings where building materials are constantly growing and shrinking.

The sealant can withstand a 25% increase (extension) and a 25% decrease (compression) in joint width. astm c920 class 25 vs class 50

Class 25 sealants are the standard for general construction. They are typically formulated from polyurethane or mid-grade silicone. for large glass panels, high-rise building facades, or

Class 50 sealants are high-performance products, almost exclusively dominated by high-grade silicones and advanced hybrid polymers. They are typically formulated from polyurethane or mid-grade

“Marcus, listen to me. You’re on the west face of that tower, right? Direct solar gain. In July, that aluminum frame will hit 160°F. At 2 AM, it might be 40°F. That joint is screaming —moving 40, 50 percent easy. Class 25 on a west-facing curtain wall? You’ll see cracks by year two. Then water gets in. Then the insulation rots. Then the lawyers come. Don’t be cheap.”

“Exactly,” Sam said. “Class 25 is for moderate climates, interior joints, or spandrel glass. Class 50 is for abuse —high rises, bridges, parking decks, anything that twists in the wind. The engineer spec’d Class 50 for a reason.”