Joints on Cellular Glass must be sealed with a ________ when applied over cold pipes.

• A. Sealant
• B. Duct tape
• C. Gas sealant
• D. Vapor barrier

Answer: (D)

Moisture control at joints is crucial when applying cellular glass over cold pipes. The joints must be sealed with a vapor barrier, a material that blocks water vapor from diffusing through the insulation. With cold pipes, any moisture trying to move through the insulation can condense inside the gaps, reducing insulating efficiency and potentially causing damage over time. A vapor barrier provides a continuous, durable seal across joints, keeping the insulation dry and performing as designed. Sealants or tapes alone may not provide a lasting vapor-tight barrier, and gas sealant isn’t a standard solution for this application.