Field Seaming: Making the Connections
Even with the world’s largest factory-fabricated panels, there will still be seams and penetrations that need to be welded in the field. These field seams are the most critical part of the installation process since a single bad weld can compromise the entire system. Getting them right requires skilled technicians, the right equipment, and precise attention to detail.
For RPE, there are two primary methods for field welding: thermal fusion (using heat and pressure) and extrusion welding (using molten plastic).
Thermal Fusion Welding (Wedge Welding)
This is the workhorse for long, straight seams between large panels.
How it Works
A specialized machine called a wedge welder travels along the overlapped seam. It uses a heated element (the “wedge”) to melt the surfaces of both liner sheets, then immediately presses them together with pressure rollers to create a homogeneous bond as the material cools. Most modern wedge welders create a dual-track weld with an air channel in the middle, making non-destructive testing easy.
Pros
It’s fast, efficient, and when done correctly, creates a very consistent, high-quality weld. The dual track simplifies testing.
Cons
Requires a relatively flat, clean, and dry surface to operate. Doesn’t work well on tight curves, corners, or around patches.
Best For
Joining the main field panels together.
Extrusion Welding
This is the “detail” welder, used for patches, corners, pipe boots, and anywhere a wedge welder can’t go.
How it Works
An extrusion welder looks a bit like a large, heavy-duty drill. It heats the base liner material with hot air and simultaneously extrudes a bead of molten RPE polymer directly onto the seam. The technician uses pressure and a PTFE shoe to smooth the bead and fuse it to both sheets.
Pros
Extremely versatile. It can be used on complex shapes, vertical surfaces, and for repairs. Creates a powerful, solid bead of welded material.
Cons
Much slower than wedge welding. The quality is highly dependent on operator skill (temperature, speed, and pressure must all be perfect). Requires meticulous surface preparation (grinding) for a good bond.
Best For
Detail work, patches, pipe boots, batten strip connections, and welding in tight corners.
Best Practices for Field Seams
Regardless of the method, a few rules always apply for seaming in the field:
Cleanliness is King
The seam area must be clean and dry. Any dirt, dust, or moisture will compromise the weld. Wipe down every seam immediately before welding.
Trial Welds are Mandatory
Before starting any production welding for the day, the technician must perform trial welds on scrap pieces of the liner. Test these trial welds on-site using destructive methods to verify the welder is set up correctly (temperature, speed, pressure) for the current site conditions.
Operator Certification
You’re lining a billion-dollar reservoir: don’t assume just anyone can run the welder. Ensure your welding technicians are appropriately trained and certified for the specific equipment and materials they are using.
TLDR: Field welding is where the rubber meets the road. Insist on experienced crews, rigorous procedures, and constant quality control. It’s the only way to guarantee a truly leak-free system.
Weather Considerations: Working with Mother Nature
Geomembrane installation isn’t an indoor sport. You’re working outside, often on massive, exposed sites, and all kinds of weather play a huge role in both the quality of the work and the safety of your crew. Ignoring the forecast or trying to push through bad conditions is a recipe for trouble.
Temperature: Too Hot, Too Cold
When you’re working with RPE, temperature dictates two things: how the material handles, and whether you can get a good weld. You need to pay close attention to the limits for both.
Cold Weather
Welding RPE in the cold is tough. The cold material sucks heat away from the wedge, making it harder to maintain a constant temperature for good fusion. Most material manufacturers set a minimum temperature (often around 32°F or 0°C) for welding activity. Below that, getting a consistently reliable weld without special measures like heated enclosures is pushing your luck. Experienced techs can compensate somewhat by slowing down and adjusting settings, but cold-weather work is always slower and demands extra vigilance on trial welds.
Hot Weather
Extreme heat brings a different challenge. The black liner absorbs a lot of sun, and even though RPE has excellent dimensional stability thanks to its scrim, it will still expand. The scrim controls this expansion, preventing the large, floppy wrinkles you’d see in a non-reinforced sheet, but still, managing these smaller wrinkles during welding takes care. Crew safety and heat exhaustion also become major factors, making early morning starts the wise play in hot climates.
Wind: Your Biggest Enemy
No joke here: Wind is actually the most dangerous and disruptive weather factor for liner installation.
Deployment Hazard
We mentioned this earlier, but picture yourself for a minute, trying to deploy a multi-ton, acre-sized panel kite in high winds. “Asking for trouble” doesn’t do it justice. It can turn the panel into an uncontrollable sail, where concerns about crew injury trump everything else. Most experienced installers set a hard limit for wind speed (often 15-20 mph), above which deployment stops.
Welding Issues
Wind can blow dust and debris into seams immediately before welding, which compromises the bond. It can also cool the welder’s heating element, making it difficult to maintain the consistent temperature needed for a good weld.
Moisture: Dew, Rain, and Snow
You cannot get a reliable weld on wet or frozen surfaces. Period.
Morning Dew
On cool mornings, dew often forms on the liner surface. Crews have no choice but to wait for the sun to dry the panels completely before starting any seaming.
Rain and Snow
Any active precipitation is an immediate stop-work condition for welding. Even after the rain stops, the liner and subgrade must be allowed to dry thoroughly before work can resume. Trying to “wipe it dry” just before welding isn’t good enough; moisture trapped in the overlap will turn to steam and create voids in the weld.
TLDR: Check the forecast religiously, respect the weather limits, and don’t try to be a hero. A day lost waiting for good weather is always cheaper than a week spent fixing bad welds or a catastrophic failure down the road.
