TPO Field Seams 

good lesson. I have few minutes to start to see your videos. I like work on top of roofing. flat roofing.

The heatgun noozle needs to go further into the lap to create an air dam which would be called a secondary weld. The primary weld is the outside inch and a half weld. I also turn the heat gun noozle in the opposite direction when welding down a seam because its easier to push the bleed out or bead from the top seam.

Cold wrlds

Now try all of this outside in the real world.