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TPO to TPO: How to Hand Weld

As always, check with your TPO manufacturer before starting any heat welding as each manufacture may have different chemical compositions which make up the TPO membrane.

This is a step by step tutorial on how to hand weld TPO to TPO. The purpose is to explain this process so a contractor could accomplish this to install our patented CGW with a TPO slipsheet.

TPO to TPO Hand Weld

What You Will Need:

  • Professional Heat Welding Gun
  • 20 mm or 40 mm nozzle for heat gun
  • Seam Roller
  • Gloves
  • Safety Glasses

Whether you’re doing a sealed seam, flashing or attached a slipsheet, you are going to want to achieve a weld between 1″-1.5″. 
Hand welding involves two stages: A pre-weld and a finish weld.

The Pre-Weld

The first weld you’re going to start with will be the pre-weld. For the pre-weld, you are going to start by placing your nozzle between the two TPO membranes at a 90 degree angle. The nozzle has a slim end which opens up to a wider fitting. You will likely want to place the nozzle under the top layer just past that angle change on the pre-weld (see photo to the right).

heat gun heat weld

Start at one end and work towards yourself. You want to give a little room between the nozzle end and the seam roller, as you do not want to “pinch” the heat. As you begin to weld by heating the membrane, always use the seam roller at a 90 degree angle to the heat gun. Slowly but consistently work your way down the seam rolling over both layers with steady pressure on the seam roller with long steady strokes till you reach the end of the seam or area you are welding. The purpose of the pre-weld is to create an air dam down the seam, to trap the air and heat to enable a good second/finish weld.


PRO TIP: While you weld, make sure to keep you gun as flat as possible so you are blowing the heat into both membranes AND towards the roller. If you angle the gun too much, you will be heating the bottom membrane more than the top and you won’t be blowing the heat towards the seam roller.

The Finish Weld

Start at the same point as the pre-weld, however this time place the nozzle between the membranes at a 45 degree angle up against the pre-weld. This weld will go a little quicker than the pre-weld. Using long consistent stokes, repeat the same process. Getting the hang of the timing will come. You want to ensure that you go at a speed that isn’t too quick where you are not creating that bond, but you also want to avoid over heating the TPO causing “bleed out” from the outer edge.


PRO TIP: When using the seam roller, ensure that you are rolling with the flat part of the roller and not the edges. Using the edge of the seam roller has been referred to as “stitching” and can create an inconsistent weld which can trap air bubbles. This was common practice in the past, however it may not be the best way to achieve a long lasting weld.


If you are a visual person, The guys at GAF Roofing have a fantastic video that shows this whole process. You can view it HERE.

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