RoofViews

Building Science

How Is the Weld Strength of TPO Tested?

By Thomas J Taylor

January 28, 2016

Testing a piece of TPO with machine test equiptment.

One of the selling points of heat-weldable single-ply membranes is that fully welded seams help create a singular membrane out of multiple sheets. There are no adhesive seams to pop loose, and a properly welded seam may provide even greater protection than the rest of the membrane because it's twice as thick. This all sounds good, but how does the manufacturer test weld strength?

Here is a look at how we test weld strength at GAF:

The first step is to weld some TPO with the same equipment and settings that are used on a roof. In fact, we make many welds at varying speeds and temperatures to cover most conditions.

welder


A strip is then cut and pulled to check quality. Here's a cross-section of what a weld cut actually looks like:


At GAF, we use machine test equipment made by Instron that enables us to measure the actual strength. The sample gets mounted between two steel jaws and pulled as shown here:


The machine records the force needed to make the pull. If you look at the center picture, you can see that the cap layer has just broken. After that, the cap peels away from the core, as can be seen in the right-hand picture. If the weld itself opens up, then it's a bad weld. The picture on the right shows what we call a film tearing bond. We've torn the cap or core film right off the membrane, exposing the reinforcement fabric. Our tester reports the force as a graph that looks like this:


This shows that it took a peak force of around 48 pound-force to break the cap or core. Then, to peel the cap from the core, it took around 20 pound-force. These are strong numbers.

We recommend roofers do a manual test weld at the start of each day, after lunch, and whenever conditions have changed. This ensures that the product welds and is the same strength day after day, mile after membrane mile!

About the Author

Thomas J Taylor, PhD is the Building & Roofing Science Advisor for GAF. Tom has over 20 year’s experience in the building products industry, all working for manufacturing organizations. He received his PhD in chemistry from the University of Salford, England, and holds approximately 35 patents. Tom’s main focus at GAF is roofing system design and building energy use reduction. Under Tom’s guidance GAF has developed TPO with unmatched weathering resistance.

Related Articles

very severe hail
Building Science

Defending Against Very Severe Hail

Think that your roof doesn't need protection against hail? Think again. Severe hail events are increasing in geographic footprint and are no longer just in hail alley. The geographic region that experiences 1 inch or larger hailstones has expanded to be nearly two-thirds of the United States. Nearly 10 percent more U.S. properties, more than 6.8 million, were affected by hail in 2021 than in 2020. Coinciding with the increase in properties affected by a damaging hail event in 2021, there was also an increase in insurance claims, which rose to $16.5 billion from $14.2 billion in 2020.

By Authors Kristin Westover

January 30, 2023

wind
Building Science

Prevailing Winds and Prevailing Codes: A Summary of Roof Related ASCE 7-22 Changes

Several changes have been included in the 2022 version of ASCE 7 as they relate to the roof. You may be thinking, 'as soon as I mastered ASCE 7-16, an updated version is set to be released!'. As with any Standard, it can be expected that updates will be made to include current research or trends. While the inclusion of tornado loads and the resulting changes in the load combinations may be the most significant, there are other updates that affect roofing as well. From minor updates to basic wind speed maps, to stepped roofs, and pavers, we have compiled a summary to help you navigate the updates. Not to fret, the changes are likely to not be incorporated until the 2024 version of IBC. However, that does not preclude incorporating these changes on current and upcoming projects.

By Authors Kristin Westover

September 07, 2022

Don't miss another GAF RoofViews post!

Subscribe now