This is a failed test-splice on a PTFE (Teflon) single-ply expansion joint belt. If you use a heat-seal iron like the one in this photo you might want to replace it with a smaller, hotter iron. A 120V extension cord can only provide so much current, so concentrate it in one spot instead of spreading it out! - INTEREP Inc.

This is a failed test-splice on a PTFE (Teflon) single-ply expansion joint belt. If you use a heat-seal iron like the one in this photo you might want to replace it with a smaller, hotter iron. A 120V extension cord can only provide so much current, so concentrate it in one spot instead of spreading it out!

This is a failed test-splice on a PTFE (Teflon) single-ply expansion joint belt. If you use a heat-seal iron like the one in this photo you might want to replace it with a smaller, hotter iron. A 120V extension cord can only provide so much current, so concentrate it in one spot instead of spreading it out!