How to Preserve Thermoplastic Roofs

Jan. 2, 2013

Patch a weldable membrane in 8 steps.

While the commercial roofing industry closely defines the polymers in manufacture of single ply roofing systems by their acronyms – such as EPDM, PIB, PVC, CSPE, TPO, and the like – from a functional point of view, these membranes are either weldable or not.

Successive generations of these polymers offer continual improvement, making today’s thermoplastic repair job relatively smooth. Ready to repair? Read on.

Innovations in Membrane Materials
PVC systems of the 1960s generally solvent-welded the seams together, using tetrahydrofurane (THF) as the welding agent. However, during application, the THF could absorb moisture from the atmosphere and contaminate the welding solution. THF also has a very low flash point. Today, heat welding has replaced solvent welding, with self-propelled hot air welding machines for field seams and hand-held welders for patching and detail work.

Another change from the first-generation PVC systems was the addition of reinforcing fabric between the facer and bottom membrane layer. This controlled the potential for membrane shrinkage upon weather exposure and improved stress distribution under wind loads. Manufacturers have since eliminated stone ballast to hold and protect the roof membrane. It was found that some ballast materials contained clay that could extract the plasticizer from the PVC compound, resulting in shortened roof life.

Mechanical Fasteners Streamline Installation
Today, you’ll likely find that most PVC and TPO membranes are mechanically fastened to the substrate. Fasteners could be placed in the seams of the membrane, so that the overlying membrane forms both the watertight seam and covers the fasteners in a single step.

Another recent innovation is to incorporate mechanically fastened stress plates that are factory-faced with polymer (TPO for TPO membranes, PVC for PVC membranes). As compared to the penetrating fasteners of earlier generations, these stress plates are placed beneath the membrane, allowing installation without penetration.

How to Patch a Thermoplastic Membrane
Need to repair your membrane? You’ll need hand or machine welders, a reliable source of power, a pressure roller and probe, and a compatible repair material. Once you’ve gathered the necessary supplies, these eight steps recommended by the National Roofing Contractors Association (NRCA) will help you patch the hole.

  1. Thoroughly clean the surface to be welded, extending the perimeter of the patch to provide an ample work area.
  2. Scrub the repair area with a solution of detergent and water.
  3. Rinse thoroughly with clean water and allow the membrane to dry.
  4. If the existing membrane surface is excessively contaminated, enlarge the hole and insert new patch material so that a weld can be made to the bottom side of the existing membrane.
  5. Wipe the area of the defect and the underside of the patch material with a clean, absorbent cloth dampened with a solvent such as acetone or MEK.
  6. Insert tip of welder into overlap area, heating and pressing the two surfaces together.
  7. After the welded area has cooled, check seams for voids with a rounded tip probe.
  8. Where patches are made with reinforced materials, seal the seams at the outer perimeter to prevent water from wicking through the exposed edge of the reinforcement.

Richard (Dick) L. Fricklas was technical director emeritus of the Roofing Industry Educational Institute prior to his retirement. He is co-author of The Manual of Low Slope Roofing Systems and continues to participate in seminars for the University of Wisconsin and RCI Inc., the Institute of Roofing, Waterproofing, and Building Envelope Professionals. His honors include the William C. Cullen Award and Walter C. Voss Award from ASTM, the J. A. Piper Award from NRCA, the William C. Correll award from RCI, and the James Q. McCawley Award from the MRCA. Dick holds honorary memberships in both ASTM and RCI Inc.

The Top 10 Most Common Roof Problems
What can you do about the problems plaguing low-slope roofs?

Balance Roofing Test Data with Performance
How to evaluate membrane roofing materials.

Roof Observers: When and Why?
Understand the role and value of roof observers.

About the Author

Richard L. Fricklas

Richard (Dick) L. Fricklas received a Lifetime Achievement Award and fellowship from RCI in 2014 in recognition of his contributions to educating three generations of roofing professionals. A researcher, author, journalist, and educator, Fricklas retired as technical director emeritus of the Roofing Industry Educational Institute in 1996. He is co-author of The Manual of Low Slope Roofing Systems (now in its fourth edition) and taught roofing seminars at the University of Wisconsin, in addition to helping develop RCI curricula. His honors include the Outstanding Educator Award from RCI, William C. Cullen Award and Walter C. Voss Award from ASTM, the J. A. Piper Award from NRCA, and the James Q. McCawley Award from the MRCA. Dick holds honorary memberships in both ASTM and RCI Inc.

Voice your opinion!

To join the conversation, and become an exclusive member of Buildings, create an account today!

Sponsored Recommendations

Building Better Schools

Download this digital resource to better understand the challenges and opportunities in designing and operating educational facilities for safety, sustainability, and performance...

Tips to Keep Facility Management on Track

How do you plan to fill the knowledge gap as seasoned facility managers retire or leave for new opportunities? Learn about the latest strategies including FM tech innovations ...

The Beauty & Benefits of Biophilic Design in the Built Environment

Biophilic design is a hot trend in design, but what is it and how can building professionals incorporate these strategies for the benefits of occupants? This eHandbook offers ...

The Benefits of Migrating from Analog to DMR Two-Way Radios

Are you still using analog two-way radios? Download this white paper and discover the simple and cost-effective migration path to digital DMR radios that deliver improved audio...