Factory vs. Field Seams: What’s the Difference?

Bill Shehane on Mar 2, 2016 8:00:00 AM

XR-5 Geomembrane Being Installed in San Diego, CATypically there are two types of geomembranes: flexible membrane liners and rigid geomembranes. With flexible membrane liners, large panels can be prefabricated prior to being delivered to the job site. Rigid membranes on the other hand have to be shipped to the job sites, where the seams are then joined together. So what’s the big difference?

Geomembrane Seams or the ‘Weakest Link?’

A geomembrane is only as good as the quality of its installation, with the seams playing a big role. If your seams are not joined properly, it could mean disaster for your project, especially if your application revolves around containing liquids like wastewater or hydrocarbons.

Field Seams

This type of seam proves to be a little bit more of a challenge during the installation process as there are many variables at play at a job site. Some examples include:

  • Rain, wind, dirt
  • Welding equipment performance
  • Temperature swings
  • Installation team changes

These variables can all affect the integrity of your field seams and should be taken into consideration during the specification stage of your project.

Factory Seams

Factory seams on the other hand are joined under more favorable conditions, typically done on a clean table or smooth concrete floor. Some benefits of factory seams include:

  • Faster and more consistent welding
  • Higher peel adhesion and bonded seam shear values
  • Lower rate of destructive testing
  • Fewer patches
  • Lower CQA (construction quality assurance) costs
  • Custom fit resulting in less detail work onsite

For some projects, flexible membrane liners can be large enough that field seams would not be required.

Inspecting Your Seams

Regardless of the type of seam, testing must occur. Depending on the size of a project, prefabricated liners can be inspected same day whereas projects with a number of field seams might need a second day of inspections - leading to increased costs. The Fabricated Geomembrane Institute (FGI) has developed some guidelines around testing seams.

Pre & Post Qualification Seam Testing

Trial seams need to be tested regarding both peel and shear strength. These seams need to be at least six feet in length as well as use the same equipment, operator, and conditions anticipated during production welding.

Production Seam Testing

The testing frequency must be once every shift change, or every four hours of production, whichever is more frequent. The same requirements as pre and post qualification seam testing also apply to production seam testing, with the only difference being that it must occur during production.

Seams should be tested anytime there is a lapse in welding due to breaks, changes in equipment (welder heats up during welding, adjustments are made to the welder slow down or lower temps sample should be tested), etc.

Overall, factory seams prove to be more consistent due to the fact that they are joined in a controlled environment. Which type of seam do you typically prefer? Share your thoughts in the comments.

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