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Heat welding is a process of thermo-fusing or heat sealing separate pieces of resilient flooring together at a seam or joint. Primarily used in commercial applications, a successful heat welded seam will provide the customer with a floor free of voids and joints where pathogens and bacteria can collect. For this reason, resilient floors with heat welded seams are sometimes referred to as seamless floors and are frequently used in areas requiring an aseptic or clean environment.

Always follow manufacturer’s recommendations when working with their products. In addition, installers should seek professional heat welding training from a trade organization, manufacturer, or a local distributor of commercial resilient flooring.

The materials used for heat welding these types of flooring are a PVC weld rod, also called a thread. There are two types of weld rod/ thread (Photo 1).

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The most common weld rod is a round solid color; the diameter can vary from 2mm to 4 mm depending on the manufacturer. The colors of round weld rod can either blend with the flooring color or contrast with the flooring color to accent a design in the flooring. Color blended weld rods will hide small imperfections in groove width and straightness while grooves must be straight and a consistent width when contrasting color weld rod is used.

Another type of weld rod is the patterned or camouflage weld rod made of the same or similar color and pattern as the flooring, this type of rod blends well with the flooring. It does not create an invisible seam however it does help to hide the seam. Depending on the manufacturer these weld rods can be a round or half round shape.

To create a successful heat welded seam, start with a well cut, well bonded seam. Most manufacturers do not recommend butting factory edges together for a heat welded seam; 1/2 inch to 1 inch should be removed from each selvage for seaming. Typically a small gap (approximately 1/64”) should left in the seam to help guide the grooving tool along the seam. If the gap is too large the seam integrity will be compromised and a heat weld failure is likely.

Depending on the manufacturer, there is typically a waiting period of 10- 24 hours to allow any residual liquid in the adhesive to dissipate prior to heat welding. Failure to allow residual liquid in the adhesive to dissipate can cause bond failure at the welded seam, which may not become apparent for several weeks to months after the installation. 

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The first step in heat welding is to groove the seam. For homogeneous sheet vinyl the groove should be 1/2 to 2/3 the thickness or gauge of the flooring and centered over the seam. A proper groove will provide the maximum surface contact between the two pieces of material to create a strong weld. If the groove is too shallow, too deep, or not centered on the seam, less surface is being welded together, creating a weak weld. The groove width should be less than the diameter of the weld rod; for example, a 3.5 mm groove will accommodate a 4mm weld rod.

There are three types of groovers used for heat welding. The hand groover is useful for short seams and the ends of seams and walls for flash coving. These tools are impractical for long seams especially when contrasting color weld rod is used (Photo 2).

The rolling groover operates without electricity; these tools have the advantage of not creating dust and noise that can disrupt an existing jobsite (Photo 3).

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Electric groovers are guided along the seam by the installer and cut a consistent groove in the seam; be careful to select a model with a dust bag and floating base to prevent digging the blade into the substrate.

Grooving and heat welding should be completed the same day to prevent contamination of grooves.

The next step is to weld the rod into the groove in the seam using a hot air gun equipped with a welding tip or nozzle (Photo 4).

 The hot air gun provides the heat and airflow required to fuse the seam together. Heat elements on these guns can achieve temperatures as high as 600 degrees Celsius; a blower transfers the heat to the groove in the seam and the weld rod.

Hot air guns are available in hand held models and automatic welders. The hand held models are useful for short seams, small jobs and flash coving, and are still needed to complete seams when an automatic welder is used.

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Automatic Welders are beneficial for long seams; they reduce ergonomic fatigue on the installer, and inconsistent welds, areas along the seam that get too hot or cold (Photo 5).

Special welding tips are attached to the hot air gun to focus the heat and air from the gun onto the groove and weld rod to simultaneously melt them together. The nozzle also allows the installer to apply a slight pressure to the weld, helping to strengthen the weld.

Welding tips can vary from a pencil tip and feed roller to all types of speed tips or roller tips. The tips are designed to accommodate different weld rod diameters and shapes (Photo 6).

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There are also tips designed for heat-sensitive flooring; these tips reduce the airflow from the gun to heat only the rod and the groove. This prevents scorching or burning of wear surfaces on the material (Photo 7).

Prior to welding the installed flooring, adjust the heat setting to the flooring manufacturer’s recommendations; if none are available adjust the heat to one half the heat capacity of the hot air gun, and allow the gun to heat up for several minutes.

Use a scrap piece of the flooring and practice grooving and welding to assure that the proper heat setting has been selected. This is an important step even when heat welding the same product on different days or jobs as temperatures, power source, and extension cord size and length can affect how the hot air gun will perform.

 Another technique that is used to determine if the heat setting is correct, is to place the weld rod in the hot air flow from the gun for a few seconds; the weld rod should melt without burning.

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Be sure to select the correct welding tip/nozzle for the materials you are welding. The tip should accommodate the weld rod; for example, half round patterned weld rod will weld best using a triangular shaped tip which prevents the weld rod from twisting and assures the correct surface of the rod melts into the groove.

Be aware that many newer commercial sheet floors are factory coated with UV cured urethane. These coatings can be sensitive to excessive heat. If scorching or cracking of the finish at the edges of the seam appears on your practice weld, adjust the heat setting, the angle of the welding tip to the floor, or use a heat sensitive type of welding tip.

To determine if the weld rod and flooring are melting together a slight ridge of material will form on each side of the weld at the juncture of the weld rod and floor. This ridge is also known as a “wash.” No wash, no weld is a practical statement when heat welding.

A heat setting that is too high or moving the gun along the seam too slowly will burn the seam. This usually occurs as a widening of the wash and develops into a charred area along the seam. A heat setting that is too low or moving along the seam too quickly will result in a cold spot in the weld. As the weld rod is being skived or trimmed it will pull out of the groove, which will require repair. In addition to establishing the correct temperature and speed it is very important to keep the welding tips clean to prevent clogging the tip which can cause the weld rod to drag and stretch or break as it pass through the tip.

Most heat welds will be accomplished in two sections along the seam and will require a splice in the weld rod in the seam. Begin the seam at the wall, weld towards the opposite wall approximately three quarters of the seam. Prepare the splice by trimming the completed end of the first weld either at an angle to the floor to create a ramp, or by using the skive knife and trim plate make the first pass along the seam, remove any loose weld rod and cut or groove the end of the weld to create a ramp for the next weld. Avoid skiving the weld flush to the floor as the splice in the weld will not hide as well.

Once this is completed begin welding from the opposite wall towards the first weld. Weld up the ramp at the splice onto the first weld approximately one inch. This technique is also used to repair cold spots along a welded seam.

When welding seam intersections such as cross seams weld the short seam first, protect the floor surface by using a skive knife or two layers of masking tape kept approximately one eighth inch from the edge of the groove, this will prevent burning the floor. Weld the seam onto the tape or metal which assures the end of the seam is welded. Then re- groove the end of the weld at the intersection of the long seam, and weld the long seam.

The process of skiving or trimming the weld rod flush to the surface of the floor will be determined by which tools are being used. If using a spatula or quarter moon knives, the seam will be skived in two passes.

The first pass is usually done while the weld rod is still warm, using a skive knife and trim plate or similar knife, trim approximately one half the excess rod. Then allow the remaining weld rod to cool completely to room temperature before making the final skiving pass, flush with the flooring surface.

These steps are very important to prevent a concave seam weld. If the weld rod is trimmed in one pass or while it is still warm, the rod will pull upward slightly as it is trimmed which will result in trimming too much of the rod. Concave seams become unsightly as dirt from foot traffic accumulates in the seam.

A note on skiving knives: they are typically sharpened on one side to allow a flush cut along the floor surface. When using a trim plate it is a good practice to have two skive knives, one used exclusively with the trim plate and one to use for the flush cut. Using the same knife for both passes can leave scratch marks on the flooring as the trim plate can leave small nicks on the knife blade.

Wiping the seam with a clean rag dampened with soap and water can help to prevent digging the knife into the surface of the flooring; however the most effective prevention is a sharp knife and a practiced hand.

The seam planer is a one pass tool that makes both cuts in one pass. When using a seam planer allow the weld to cool completely before skiving. Seam Planers that are adjustable will prevent digging in or skips when skiving. As with the skive knives, maintain sharp, clean blades on seam planers (Photo 8).

When skiving and any repairs are completed, depending on the product and manufacturer there may be additional requirements of heat glazing the weld rod.

The heat glazing process is accomplished using a hand held hot air gun with a pencil tip set to a lower temperature. Hot air is focused along the finished weld giving the weld a glossy appearance this slightly consolidates the weld rod which helps to keep it clean. Additionally some manufacturers may require a treatment of chemical seam sealer on the finished weld. Finally it is a good practice to apply a coat of commercial floor sealer or polish over the seam to keep it clean until construction is completed and regular floor maintenance begins.