Hot-Air Welding Under Changing Environmental Conditions

The robotic welder’s speed, heat output and pressure should be properly programmed before the welding process begins. Photo: Leister.

The robotic welder’s speed, heat output and pressure should be properly programmed before the welding process begins. Photo: Leister.

Today’s most powerful hot-air welders for overlap welding of thermoplastic membranes are advertised to achieve speeds of up to 18 meters (59 feet) per minute. That’s fast enough to quickly ruin a roofing contractor’s day.

These robotic welders are digitally monitored to achieve consistent overlap welding performance, but they cannot adapt to changing environmental conditions automatically. It’s the contractor’s job to monitor and assess seam quality before the base seam is welded and when ambient temperatures or other factors potentially influence welding performance.

Successful hot-air welding requires the use of specialized, properly maintained and adjusted equipment operated by experienced personnel familiar with hot-air welding techniques. Achieving consistent welds is a function of ensuring that the roofing membrane surface is clean and prepared for heat welding, conducting test welds to determine proper equipment settings, and evaluating weld quality after welding has been completed.

Setting up hot-air robotic welders properly is the key to having a properly installed thermoplastic roof, and performing test welds is one of the most important steps. Making appropriate adjustments before the welding process begins ensures that the correct combination of welder speed, heat output and pressure is programmed into the robotic welder.

For most roofing professionals, these procedures have been firmly established in the minds of their crews and equipment operators through education and field training. But let’s not forget that Murphy’s Law often rules on both large and small low-slope roofing projects.

The frightening reality about using robotic welders is if they are set-up incorrectly or environmental conditions change, the applicator may weld thousands of feet of non-spec seam before anyone even bothers to check. If you probe for voids at the end of the day, it is probably too late.

If serious problems are discovered, the applicator must strip in a new weld via adhesive, cover tape, or heat welding, depending on what the membrane manufacturer will allow. If seams must be re-welded, the operator has to create not one, but two robotic welds on each side of the cover strip. The sheet will also need to be cleaned and re-conditioned no matter what method is used.

Can these errors be corrected? Absolutely. Except now the crew is in a real hurry because the roofer is working on his own time, and application errors tend to snowball under these conditions.

Reality Check

What goes on in the field is sometimes quite different than what one sees when hot-air welding thermoplastics under an expert’s supervision.To support this view, we asked four field service reps, each with a minimum of 35 years of roofing experience, to comment. The most senior “tech” has worked for six different thermoplastic membrane manufacturers in his career. Their names shall remain anonymous, but this writer will be happy to put readers in touch with them upon request.

Successful hand welding is a skill that is developed and refined over time. The correct selection of welder temperature and nozzle width can have a significant effect on the quality of the hand weld. Photo: GAF.

Successful hand welding is a skill that is developed and refined over time. The correct selection of welder temperature and nozzle width can have a significant effect on the quality of the hand weld. Photo: GAF.

So, let’s welcome Christian, Dave, Mark and Walter, and get straight to the point: Is the average roofing crew diligent enough when it comes to properly testing welds using industry best practices?

“I would say ‘probably not,” exclaims Walter. Dave just shakes his head as his colleague Mark adds, “I would have to say no.”

Considering the generally laudable performance of thermoplastic membranes over the last decade or so, we must interpret our experts’ opinions as suggesting the need for further improvement in hot-air welding techniques. Hence, the purpose of this article.

“There are a few outstanding issues causing bad welds,” says Walter. “These include welding over dirty or contaminated membranes; improper equipment setup; using crews with inadequate training; and knowing the difference between the weldability of various manufacturers’ membranes.”

Welding equipment consists of three main components: the power supply, the hot air welder (either automatic or hand-held), and the extension cord. A stable power supply of adequate wattage and consistent voltage is critical to obtaining consistent hot air welds and to prevent damage to the welder.

The use of a contractor-supplied portable generator is recommended, although house-supplied power may be acceptable. Relying on power sources that are used for other equipment that cycle on and off is not recommended. Power surges and/or disruptions and insufficient power may also impact welding quality. Proper maintenance of welding equipment is also of obvious importance.

“Contractors seem to never have enough power on the roof,” observes Mark. “The more consistent your power is, the more consistent your welds will be. Too many times, I’ve seen too many tools (hand guns, auto welder, screw guns and a RhinoBond machine) plugged into one generator.”

Generator-induced challenges on the jobsite are going to arise, agrees Christian. “But at least today there is more experience in understanding, dealing with, and ultimately preventing these issues,” he says.

Most TPO and PVC membrane suppliers also recommend using the latest automatic welding equipment, which provides improved control of speed, temperature and pressure. Our four experts generally agree that field welding performance has improved over the years and programmable robotic welders have helped. They also point to proper training and experience as crucial factors.

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Roofing Adhesive Features One-Step Application Process

Helix Low-Rise Adhesive is ready to use from the container, no mixing required.

Helix Low-Rise Adhesive is ready to use from the container, no mixing required.

With a one-step application process, Helix Low-Rise Adhesive from Mule-Hide Products Co. provides adhesion of approved roof insulations, thermal barriers, cover boards and fleece-backed single-ply membranes to a variety of roofing substrates.
 
The polyurethane foam is applied in a single step. Both parts of the adhesive are ready to use from the container – no mixing required – and are applied simultaneously in a 1:1 ratio through a static mix tip. It is applied in continuous ribbons or beads spaced 4, 6 or 12 inches apart, depending on the project and code requirements. There is no overspray, and it cures in minutes.
 
Helix Low-Rise Adhesive contains no volatile organic compounds (VOCs), chlorofluorocarbons (CFCs) or hydro chlorofluorocarbons (HCFCs). 
 
It does not require mechanical fasteners, maintaining a puncture-free vapor retarder, preventing thermal bridging and protecting the structural integrity of the roof deck.
 
The bond created by Helix Low-Rise Adhesive provides wind uplift resistance, allowing it to be used on buildings in higher wind zones. In addition, it provides hail resistance when used as an adhesive for fleece-backed membranes.
 
Helix Low-Rise Adhesive comes in cartridge twin-pack tubes or two-tank sets. Both include one container of each of the adhesive’s two components – Part A and Part B. Cartridge twin-packs cover approximately 200-600 square feet of roof and tank sets cover approximately 1,000-3,000 square feet of roof, depending on bead spacing.
 
The cartridges fit most dispensing guns currently available on the market. Tank sets come with a Helix Gun Assembly (25-foot dual-hose with attached spray gun), petroleum packet, wrench, and 10 Tank Static Mix Tips. Contractors need not purchase specialty pumps or spray rigs. No external power source is required to run application equipment.

Ease Single-ply Membrane Welding

Miller Weldmaster has introduced Seamrover DD, a dual-direction roof welder to increase operational ease of single-ply membrane welding.

Miller Weldmaster has introduced Seamrover DD, a dual-direction roof welder to increase operational ease of single-ply membrane welding.

Miller Weldmaster has introduced Seamrover DD, a dual-direction roof welder to increase operational ease of single-ply membrane welding. An automatic floating nozzle ensures the Seamrover DD applies uniform welds, and a flexible core weld roller allows the Seamrover DD to accommodate any roof surface. The tool can be used in a forward or backward direction for long, straight consistent seams; reduced welding time; and increased seam visibility.

OMG Roofing Products Releases Video on Installing Thermoplastic Single-ply Membranes

OMG Roofing Products has unveiled a video showcasing how easy it is to install thermoplastic single-ply membranes on standing-seam metal recover projects using the RhinoBond induction welding system.

OMG Roofing Products has unveiled a video showcasing how easy it is to install thermoplastic single-ply membranes on standing-seam metal recover projects using the RhinoBond induction welding system.

OMG Roofing Products has unveiled a video showcasing how easy it is to install thermoplastic single-ply membranes on standing-seam metal recover projects using the RhinoBond induction welding system. The video offers a step-by-step demonstration of the application and highlights the ways the RhinoBond System eliminates the traditional hassles of this type of application, including the following:

  • No special width membrane needed.
  • No membrane to install between purlins.
  • No penetrations of the new membrane.
  • No excess membrane buried in the laps.
  • No membrane orientation issues.
  • No fastener jacking.

Watch the RhinoBond standing seam video.

GAF Completes Extensive Roof Replacement Project at Corporate Headquarters

GAF has completed an extensive roof replacement project at its new corporate headquarters at 1 Campus Drive in Parsippany, N.J. GAF has been relocating to the new property, which has been completely renovated with quality products in all areas—including, of course, the roof.

GAF worked closely with its Master Select Contractors to ensure the installation of an energy-efficient roofing system at 1 Campus Drive. The system included GAF’s RUBEROID HW 25 Smooth Membrane, EnergyGuard Polyiso Insulation (for high insulation value), and EnergyGuard HD Cover Board (which offers a high R-value and impact resistance). It also included GAF’s single-ply membrane, EverGuard Extreme Fleece-back TPO Membrane. GAF is proud of how EverGuard Extreme Fleece-back TPO Membrane outperforms competitive TPO membranes (based on heat-aging tests), and backs it with a commercial roofing guarantee.

As GAF prepared to move into its corporate headquarters, it was imperative to make sure they had a durable, energy-efficient and easy-to-install roofing system. The combination of GAF EverGuard Extreme Fleece-back TPO Membrane in 2-Part Roofing Adhesive over EnergyGuard HD Cover Board and EnergyGuard Polyiso Insulation set in Olybond, along with RUBEROID HW 25 Smooth Membrane was the perfect system to keep its building dry and comfortable for years to come.

When using EverGuard Extreme Fleece-Back TPO Membrane with Low-Rise Foam Adhesive (compared to EverGuard Extreme Smooth TPO Membrane), the fleece on the back of the membrane provides an added cushioning layer, especially for hail-prone areas. Also, when combining EverGuard Extreme TPO Accessories with EverGuard Extreme Fleece-Back TPO Membrane, it helps save labor (versus field fabrication)—and provides an overall cleaner-looking roof.