By Ray Thompson, Jr.
The heat welding process arrived in North America in the late 1980s. The main reason for the change was to ensure seam integrity and to produce an aseptic-free seam. In addition, there was a major move from felt-backed to vinyl-backed materials. In my travels looking at commercial resilient concerns, I am constantly encountering failures with the heat weld process. As such, I’ve developed a list of these failures. In no particular order, they are:
Moisture Conditions in Slab
A moisture condition in the slab will migrate towards the seam. If the condition exists, it too can cause moisture vapor that will stop the thermo fusion process from thoroughly taking place. If the thermo fusion process is not completed, the seam weld will fail.
Adhesive Not Dry
Manufacturers recommend a minimum amount of time between the installation and the start of heat welding, generally overnight. The exception to this is to use a dry-to-touch adhesive at the seam. The reason: the high heat from the welder will cause any moisture in the adhesive to turn into moisture vapor that will stop the thermo fusion process from thoroughly taking place. The time between the installation and welding is worth the wait.
Straight Edge and Butt
Many installers use the straight edge and butted seam. They use this method not realizing the seam edges are gapped in some areas and tight in others. When the groove is cut in the seam – where the edges of a seam are not evenly spaced or the groove is not centered on the seam – it will leave one side of the groove without a radius at the base of the groove. The radius at the bottom of the groove is extremely important to the integrity of the seam weld. Without the groove at the weld base, undue stress to the seam edge will usually result in a failure of the weld.
Moving Too Fast
Installers weld at different rates of speed. They need to know their speed and work at a speed consistent with their heat setting. Installers that change speeds will find the integrity of the weld will change along the seam. These changes can range from scorching to poor fusion.
Sudden Movement of the Welder
An installer will generally reach out and pull the heat welder towards their body. As the welder gets closer, the installer will move. When they move, it is necessary to maintain a constant fluid movement. Any sudden movement will cause a jump at the weld tip. This will generally leave about a 2″ loose spot and a weld failure. If this happens, the installer needs to remove that section and re-weld it. It is a simple process often overlooked.
Groove Cut Too Deep
Manufacturers recommend grooves to be half to two-thirds of either the thickness of the wear surface on materials with a backing, or the thickness of the material in vinyl-backed products. With vinyl products, the installer must adhere to those specifications. I have seen grooves cut completely through the material into and through the adhesive line into the substrate. Many installers confuse linoleum seams with vinyl seams; linoleum seams are grooved, down to, but not into the jute backing. If that is done with sheet vinyl, the welded seam will likely fail.
Groove Cut Too Wide
There are several diameters of weld rod available in the market place. If a groove is cut in the material too wide for the rod, the weld will be compromised. As the installer, you need to double check the rod with the groover width prior to the start of the grooving.
Contamination of Groove
Some installers will tend to groove the entire area prior to the start of heat welding. This exposes the seam to contamination from dirt getting into the groove prior to the start of the heat welding. Sweeping the grooves with a broom contaminated with some type of sweeping compound and construction traffic will result in failure. Other situations occur when the seams are covered with tape. Adhesive residue on the tape will affect the material and/or the groove.
Poor Power Source
On many commercial installations, the power sources are a considerable distance from where the heat welding is taking place. When this is the case, a heavy-duty power cord that can handle the high volume of power necessary to run a heat weld gun will be necessary. An insufficient amount of power will affect the performance of the heat welder. If there is insufficient amount of power or a weak power source, the heat weld gun will surge. If the heat weld gun is surging, seek an alternative source of power.
Poor Heat Setting
Allow the heat welder to thoroughly heat up. Don’t become impatient and start to heat weld before the unit is totally warmed up. Starting to weld too soon will result in rising temperatures and the surface of the material scorched. Make sure to set the temperature high enough to thoroughly melt the weld rod. Failure to do so will result in a poor fusion. The temperature setting is a small window between a good fusion and a poor fusion. Another factor is the temperature of the substrate. A cold substrate requires more heat. Obtaining the correct setting requires experience on the part of the installer.
Crowding One Side of the Groove When Welding
Some installers tend to hold the heat welder on an angle, crowding one side of the seam. This will cause the seam to be weak along one side of the seam. The heat welder should be held straight up with a firm, but not hard, pressure on the weld tip. Too much downward pressure on the tip will tend to stretch the rod. When the weld rod cools, it wants to shrink and creates undo stress to the weld.
Improper Weld Tip
Weld tips should be designed for the rod and type of material being welded. The flow of the heat must be focused at the bottom of the groove as well as heating the rod. One of the worst problems with the hot air distribution is too much hot air wash, scorching or distorting the coating on the wear surface of the sheet material.
Skiving too early
The skiving process needs to be done in two passes. Some installers try to eliminate the first pass to save time but the end result is not worth cutting corners. On the other hand, the skiving of the first pass in sheet vinyl seams need to be delayed until the material is cooled, normally 10-15 minutes. The final pass should be done when the seam is thoroughly cooled, normally 20-30 minutes. In situations where the final skive has been rushed, a seam in a vinyl product may be severely concaved. Heat welded seams will have a minor concaving, but severe concaving will result in a maintenance issue.
Heat welding is an art performed by an experienced professional. Installers that have perfected the art of heat welding, pay strict attention to all of the job conditions, and know how to compensate for the changes they will encounter. Few installers with minimal experience can go out to a jobsite and have a successful heat weld performance. Heat welding requires technique. Experienced installers occasionally experience difficulty, especially when heat welding flash coving, inside and outside corners. A properly heat welded vinyl seam will be almost as strong as the material without a seam.