TECH TALK:September 2025
TPO is a very popular membrane option that can be found in every region of the country. The differences between Thermoplastic Membranes (TPO & PVC) and Thermoset Membranes (EPDM) could be a Tech Topic article of their own, but one of the main differences is the method of splicing sheets together to create a continuous, watertight roof.
Thermoplastic membranes are spliced together by heat welding, a process that utilizes a heat gun and silicone roller. The heat gun is placed precisely between the top and bottom sheets of the membrane overlap, and the silicone roller is used to “mate” the sheets. Once the sheets are heated to the correct temperature and proper pressure is applied, the top and bottom sheets bond together to form one monolithic sheet of membrane. This procedure applies to splicing field sheets together as well as all other TPO detail applications (T-joint covers, wall flashings, pipe flashings, etc.).
Although it sounds simple, many variables can cause a heat weld to fail. These include—though are not limited to—incorrect welder temperature, improper airflow, lack of pressure when rolling, unreliable power sources, and dirty seams due to improper cleaning. That being said, heat welds perform very well when done properly. Robots, or automatic welders such as the Leister Varimat V2, help reduce the risk of human error through proper calibration prior to welding. Unfortunately, these robots are limited to field seams—which is not where most leaks occur.
One way to reduce the risk of poor heat welding procedures when installing details on a TPO roof is by utilizing Sure-White EPDM products. Carlisle accepts Sure-White EPDM products on TPO projects with warranties up to 20 years. These products can be installed on TPO projects both during production and when making repairs. Field-wrapped pipe penetrations, metal edge overlayment, T-joint covers, and many other details can be completed to meet minimum warranty requirements with Sure-White EPDM products in lieu of TPO products.
Some of the advantages of using Sure-White EPDM on TPO projects include:
Easier installation of pressure-sensitive products compared to heat welding
Elimination of some human error factors mentioned earlier
No need for a reliable power source or extension cord
Useful for production crews with limited experience installing thermoplastic roofing systems
Sure-White EPDM is an excellent solution for TPO roofs—especially for contractors that install both EPDM and TPO systems and are already familiar with EPDM products. However, a few important considerations should be noted when installing Sure-White EPDM on TPO roofs:
Sure-White EPDM is not acceptable on warranted PVC projects when used with Carlisle’s 2-Step Activator & Primer.
TPO Primer or Low-VOC EPDM & TPO Primer must be used in lieu of HP-250 Primer.
White Lap Sealant is still required around all edges of Uncured Elastoform Flashing.
A heat gun should be used when installing Sure-White Elastoform.
Sure-White EPDM applications can only be used on TPO projects with warranties up to 20 years, with the following exceptions:
Detail U-18CT Scupper with EPDM Flashing (30-year detail)
Detail U-8C CFA Certified Pre-Fabricated Square Tube Wrap (30-year detail)
Below this paragraph is a collection of the most popular details utilizing Sure-White EPDM on TPO. Additional details can be found in Carlisle’s Specification and Detail Book in the TPO section under Attachment II: TPO Flashing Procedures Utilizing Sure-White EPDM Flashing Products.
Sure-White EPDM products should not be overlooked on warranted TPO projects. They are problem-solvers, easy to install, and excellent repair materials that every Service Department should keep in their warehouse and trucks.
If you have any questions about this article, please contact Dane Helnore at CSL West.
For any questions, please contact Dane Helnore at CSL West. Your local Field Service Representative is also an excellent resource for identifying, approving, and explaining details that may serve as effective solutions on your next project.