We heat the seams briefly by slipping a torch nozzle under the membrane edge, and then immediately press the pieces together using a seam roller. You should see a little bit of white smoke wafting out of the seam as you work. 

We use a Leister hand-held, 1,500W torch, with power adjustable from 80W to 1,500W, and a temperature scope from 100°F to about 1,300°F. (On smaller jobs like this one, the hand-held torch is sufficient, but on large, commercial-scale work, we break out the “robot,” which semi-automates seam welding and can crank along at up to 10 feet per minute.) While cold weather doesn’t delay installation (you can even weld PVC in the rain), you do have to adjust the welding temperature upward to compensate. Likewise, in hot weather, you need to lower the welding temperature accordingly. 

What you’re looking for is a characteristic “bleed” at the seam edge, where molten material is squeezed out ahead of the seam roller. That tells you that you have a fully welded bond. We use a pointed probe to check for any loose spots that would void the manufacturer’s warranty.