Astm C920 Class 25 Vs Class 50 May 2026

He grabbed a scrap of aluminum and a tube of each sealant from the sample kit. Outside, he rigged a crude test: two panels with a 1-inch gap. He applied Class 25 on one, Class 50 on the other. Then he used a heat gun to simulate the west-face solar load, followed by a can of freeze spray.

Pat laughed. “Because I don’t trust the installation crew to keep the joint width perfect. Class 50 forgives a ½-inch joint that’s actually ⅝ inch. Class 25 demands precision. Also—check the building’s wind-sway calculation. At the 30th floor, the deflection is 2 inches. That joint is moving ±45% on the corners. Class 25 would be at 180% of its limit. It’s not a matter of if it fails—it’s when .” astm c920 class 25 vs class 50

The Sealant That Saved the Tower