Equipment Notes: Hot Air Welding

Choosing the Right Welder for the Job

by Jeffrey R. Meinhart, director of sales & marketing, Roofmaster Products Company









(Editor’s Note: Jeffrey R. Meinhart has been with Roofmaster® in his current position for the past 20 years. Previously, he held senior sales and marketing management positions in the pharmaceutical and consumer products distribution industries. Meinhart can be reached at


There are many types of roofing systems. The systems that now have the largest market share are the single-ply membrane systems. These are usually non-asphalt-based materials. The most common ones today are made of TPO, PVC, or EPDM. Many roofing contractors are looking to install single-ply systems more and more because less equipment is needed and the apparent ease of installation is attractive to many. Single-ply systems don’t require a kettle, on-deck hot asphalt equipment, mops, and pose fewer safety problems than hot asphalt installations. They are a factory-made roofing system rather than an onsite system such as BUR. There are advantages to both single-ply systems and BUR systems. Single-ply systems provide only one level of protection unlike a BUR system that has multiple layers of protection. Because of this, extra care must be taken to avoid punctures or other types of damage. Wherein a single-ply system may cost more for material and less for labor, conversely a BUR system may cost less in material and more in labor.

EPDM membranes are thermosets. Thermosets cannot be hot air welded. Either a two-faced tape or contact cement must be used to weld the lap seams to make them completely waterproof. They come in both unreinforced and reinforced. The reinforced membranes are more resistant to tearing than the unreinforced. They are offered by most manufacturers in several widths including up to 50′ wide for large areas.

PVC and TPO membranes are thermoplastic membranes. Unlike EPDM, these membranes usually have their seams welded by hot air welders. This is accomplished by passing the hot air welder’s nozzle slowly between the upper and lower edges of the membranes causing them to slightly melt or soften. As they are pulled together, they tend to physically and chemically bond together into a completely waterproof edge. Usually a small hand roller is passed over the seam simultaneously as the seams are heated and pressed together to ensure a complete bond. After the seams have cooled, it is suggested that all seams be tested with a seam-tester to ensure there are no voids within the welded area. A seam-tester is a pointed icepick-looking tool with the end bent to 90° to easily slip under the membrane edge to find any voids in the weld.

When it comes to securing the finished membranes to the roof deck or substrate, the methods that can be used are mechanical, fully adhered, or glued and ballasted. Usually a ballasted system is the least expensive to install, although costs will vary by region and labor rates, followed by mechanically adhered, then fully adhered. Many variables will dictate which type of installation method should be used including climate conditions, substrate, roof configuration, roof application, and of course, specifications. If an architect or roofing consultant is involved, this usually will be called out in detail. If this is left to the roofing contractor, it is strongly suggested that the membrane manufacturer be contacted for complete installation specifications for that application.

When hot air welding equipment is warranted, either a handheld or automatic welder can be used. The handheld models are generally used for small jobs and around roof protrusions and edges. The automatic welders are generally used on large jobs where long seam welds are the norm. With the automatic welders the membranes are laid out, the nozzle placed between two sheets, and the operator merely guides the automatic welder along the seam. The automatic welder heats the seam and presses it together, all in one fluid motion. It’s almost impossible to make a bad weld with an automatic welder when the machine is set up properly.

If a roofing contractor makes the decision to get into single-ply membrane installations, they can expect to invest several hundred dollars for a good-quality handheld welder, and several thousand for a good-quality automatic welder. Additionally, since this equipment is electrically operated, depending on available onsite resources, a gas-powered generator may also be required. When using an automatic welder with handheld units, a generator no less than 12kw with dual capability, 220V, and 110V, is recommended, whether purchased or rented. This size generator will provide power to operate one automatic welder, 220V, and two handheld welders, 110V. Also, remember to include a very heavy-duty power cord. Get nothing less than a 10-3 wire, 300V extension cord to go as long as 100′.