Joe Knows Granule Surface Preparation: Torch-Applied


Welcome back low-slopers!

In this session, I will show you how to properly prepare underlying granulated surfaces when torch applying Flintlastic® GTA, GTA-FR, and GTS-FR.

These steps should be utilized for end laps as flashing details to ensure a long-term bond. This step is supplementary to construction details CT-22, CT- 06, CT-09, and CT-10

How it Works

While installing base flashing, end laps, or other details, it is common to layer portions of the cap sheets on top of the granulated surface when torch-applying APP or SBS-modified bitumen roof systems.

Once they are welded together, they will form a seal. The torching process then locks the bitumen to the cap sheet and bonds it to the base sheet creating a watertight seal.  

Follow These Steps for Success!  

1. First, use a torch to heat the granulated surface that will be overlapped. Be sure to use caution as you do not want to burn through the cap sheet.

2. Now that the cap sheet is warmed, use the back end of a trowel to press the granules into the sheet. This will create a smooth and tacky surface.

3. Lastly, you will need to torch-weld the overlapping sheet. You will know a weld is adequate when a flow of melted bitumen compound flows evenly in a one-quarter to one-half inch uniform bead. The bitumen will then seep from the applied membrane’s edge.

Excellent job. You and your team have learned the next steps for crucial installation details. If you have any questions, you can submit them via this form or comment below. 

For additional information on CertainTeed products and installation, please visit

In the meantime, keep an eye out for my next blog and video post detailing the installation method Self-Adhering Surface Preparation.

Starting at the beginning? We’ve got you covered.

Commercial Roofing Construction Detail CT-22: Installing Membrane End Laps

Commercial Roofing Construction Detail CT-06: Base Flashing on a Parapet Wall

Commercial Roofing Construction Detail CT-09: Base Flashing the Inside Corner of a Parapet Wall

Commercial Roofing Construction Detail CT-10: Base Flashing the Outside Corner of a Parapet Wall

Happy Building, 


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