Whether hand grooving or using a machine, make sure the groove is the appropriate depth for the flooring and the appropriate width to accept the welding rod being used.

The welding speed and heat gun temperature are adjusted based on site conditions and the individual installer. The tip of the welding gun must not be too large for the rod being used. A practice session makes sure everything is right.

Heat welding seams in resilient sheet flooring or tile is one of the more specialized talents an installer can possess and is a service that a dealer or flooring contractor can offer for a virtually “seamless” floor.  A great deal of skill is involved, so not a lot of installers do heat welding.  The ones who can weld are in demand because health care continues to be a strong market for resilient flooring and that is the number one area where heat welded seams are called for.  I find that a lot of dealers and flooring contractors don’t understand the procedure so they are reluctant to get involved in projects that include welding.  They just don’t bid these projects, which is smart if you don’t have the ability to do the work.  However, in other cases they talk the customer out of heat welding and switch them to a chemically sealed seam so they CAN bid on the job, which may impact the overall integrity of the installation.  In this column we will cover some “how to” for installers and for flooring contractors and some points to avoid problems.

When I was active in the retail side of the business I had no experience with heat welding because most of our business was residential.  So, I would have been one of those dealers that stayed away from jobs that had welding. I spoke with Gerry Swift, vice president for the Commercial Division of Mike’s Flooring Companies and the Chairman of FCICA, The Flooring Contractors Association. We’ve known each other for several years now because of our work with this great flooring trade association that focuses on education and networking for all things commercial.  Mr. Swift has a lot of experience in the commercial market in the Washington, D.C. area but admitted, “As a commercial flooring contractor without an installation background, heat welding resilient seams is something I used to handle with a scale ruler and calculator.” This is an example of a middle ground where the dealer knows he has installers that can handle the work, but Mr. Swift admits, “I didn’t understand the true value of heat welded versus chemically welded seams.”

A shot of hot air known as “glazing” melts the surface of the weld, darkening the color and making the weld less porous.

The value of heat welded seams is most evident in health care installations and other high traffic areas, where floors are subjected to heavy rolling loads or for floors that are frequently washed or wet. Design elements such as pinstriping, color accents or way-finding elements such as arrows or words can be accomplished using contrasting heat weld thread (also known as heat weld rod) or even “glow in the dark” rods for emergencies.  The alternative to heat welding is chemical seam sealing (also called chemical welding or cold welding) which, when done correctly can make a very strong seam.  However, most specifications and even some building codes insist on heat welding in certain types of areas so a chemical weld is not an accepted alternate in many cases.

When I started working on the commercial side in 1992 as a resilient manufacturer’s technical representative, I started to hear a lot more about welding and had to diagnose problems on installed jobs as an inspector.  I recently spoke to a full time inspector, Claudia Lezell of Inspections Too.  I first met Ms. Lezell in 1996 when we began working as vounteers to develop the Resilient Floor Inspector Certification program for The Clean Trust (formerly IICRC). As a full time inspector, she does troubleshooting of seam failures way more often than I do.

Intermittent gapping such as this can be caused by uneven grooving or by speeding up and slowing down during the welding process.  A steady speed is critical.

  “From an inspector’s point of view,” said Ms. Lezell, “diagnosing a heat weld seam failure involves re-constructing the seaming process to see how the seams were trimmed and grooved, how fast the installer moved, the temperature of the welding gun and even whether the right welding rod was used in the first place.”  That pretty much sums up the process and what can go wrong with heat welded seams.

The heat weld procedure is fairly simple, but that doesn’t mean it’s easy.  The floor is installed and the seams are cut as they normally would be.  Don’t make the mistake of not trimming the factory edge.  The idea that the heat welds somehow “cover all sins” at the seam is not correct so butting factory edges together is not acceptable. Neither is leaving a gap at the seam to make the edge easier to follow. The two pieces of material need to be touching each other for the maximum strength at the seam. Leaving more than just a knife blade thick gap or using factory edges instead of trimming the seam will still give a good looking seam so you will get off the job, but over the long term these are shortcuts that can cause a seam failure.  Cut and trim the seam exactly as the manufacturer recommends.

Gapping along the entire length of the seam can be caused by welding too fast or by using too wide of a groover.

“Don’t forget to mention contamination,” Ms. Lezell reminded me, “which can cause complaints on any kind of seam, whether it’s heat welded, chemically sealed or not sealed at all.” That’s a great point and another reason to trim the factory edges – to make sure you are sealing clean material. Even more important, keeping adhesive out of the seam is so critical to success because this can affect the bond of whatever seam sealing method you use or create a dark line on a seam that doesn’t get sealed. Many complaints on seams can be traced to adhesive in the seam.

Once the seam has set, the heat welding process can begin, usually the day after flooring is installed to allow adhesive to dry.  However, I covered new adhesive systems a year ago here in “Resilient Adhesive Update,” FCI December 2010. Some adhesives such as spray adhesive, pressure sensitive or dry “tape” systems may allow for welding the same day as installation.  To be sure, check with the flooring and/or adhesive manufacturer. Whether it’s the same day or the next, once the recommended time has elapsed, grooving (also called routing) is the first step in the welding process.  Some tile products are grooved at the factory, but in most cases grooving is done on the job.  It’s a fine art, sometimes done by hand (as shown in Photo 1) and sometimes done by automatic machines.

Trimming before the weld has cooled can result in a concave weld.  The gully that is created will often collect dirt and become unsanitary.

The advantage to hand routing is being able to follow the seam edge and any slight undulations in the floor surface.  The advantage to automatic routers or welders is speed. There is no right way to do it and either method has its challenges and takes practice to master.  Once the seam is grooved, a welding rod (also called welding thread) is melted into the groove. Welding rods come in a variety of different sizes, so the size of the groover and the welding tip on the heat gun are very important.  Refer to the specifications for the product you are installing to be sure you don’t groove the seam too wide or too deep.  For example, if you worked with a 5 mm diameter rod in the past and grabbed the same equipment to do a seam that uses a 4mm or 3.5 mm rod, you’ll have too large a groove.  The rod won’t fit, and there is no way to correct that. The same holds true regarding the tip on the hot air welding gun, as shown in Photo 2. Too wide a tip can actually burn or distort the flooring material because too much hot air goes through.  Using the same example, a 4mm welding rod being passed through a 5-mm tip leaves a lot of extra hot air coming in contact with the flooring and that can cause damage.  Having the right equipment is critical.

One of the most common questions is, “What temperature should I set my heat gun for welding?”

The answer to this question will vary depending on factors such as the temperature of the room and the substrate, how fast the installer moves down the seam and even the length of the extension cord that can reduce power to the heating element.  Generally, the faster you move the higher the temperature should be. However, with all these factors affecting the process on a job to job basis, no two installations are exactly the same. It’s important to practice on some scrap material before welding the seams so the temperature of the gun can be adjusted.  Make sure you have all of the right tools and practice for ten minutes or so. Even experienced installers always take a practice run to be sure everything is just right.

Another big question is regarding the differences in welding vinyl (also called PVC) products versus other materials such as rubber or natural linoleum.  John Kozak is manager of technical support for Johnsonite who I’ve known since the 1980s when he was here in New York in the technical department at Kentile. Today he is based at the Azrock plant in Houston, Texas.

   “The major differences,” Mr. Kozak said, “are that when welding PVC you truly get a seamless joining of the adjacent pieces – an actual physical melting of the vinyl floor to the PVC welding rod.” Done correctly, you actually melt the welding rod and the vinyl floor, truly welding everything into one continuous floor covering.  “Now when it comes to heat welding linoleum or rubber,” Mr. Kozak continued, “you are basically using a hot melt adhesive rod to accomplish what is mainly a physical glue bond.” So, rubber and linoleum get heat welded by a similar looking procedure to vinyl but rather than melting the materials together, it’s gluing them together with a hot adhesive. It seems like a subtle difference but it’s important not to get the materials mixed up, Mr. Kozak emphasized, “Regarding the welding rods that are used, PVC rods and those for rubber or linoleum are not interchangeable.”  Again, make sure you have all of the right materials and follow the manufacturer’s guidelines because there can be subtle differences from one product to the next.

Once the welding is done, the rod is trimmed flush with the surface of the flooring using a “spatula” knife designed just for this purpose. This is another area where rushing can cause a failure. This process is also called “skiving” and is done in two steps. The first pass uses a “trim plate” so that the blade trims most of the welding rod but leaves it slightly higher than the flooring.  The second pass, without the trim plate, brings the weld flush to the surface of the flooring material.  This last pass is made easier by wetting the area with some soapy water to provide lubrication for the blade.  This can minimize the chance of the blade digging into the surface of the material.  Again, vinyl products versus rubber or linoleum are done two different ways, as explained by John Kozak.  “Both are skived using the two pass method, but with PVC the first pass is done while the rod is warm and the second is after the rod has cooled. With linoleum or rubber, both passes are done cool.”  The reason for the two-pass process is to allow the rod to “relax” because heat causes the welding rod to expand.  If you trim a warm weld flush with the floor and it continues to relax, you’ll wind up with a “concave” seam, or a little gully that will catch dirt and cause a complaint.  

The final step is optional “glazing” of the weld with hot air to darken the color. Take the weld nozzle off and apply heat to the surface of the weld, as shown in Photo 3.  This will make the welded seam smoother, less porous and less noticeable.

If you don’t know how to weld, what’s the best way to learn? If you can team up with an experienced installer that’s a great way to learn, or attend training schools offered by manufacturers who teach welding in their classes.  There are also industry training events, as Gerry Swift explained.

“It wasn’t until I attended an FCICA convention in 2005 that I saw this highly skilled work demonstrated by Pete Austin, now with Gerflor USA,” Swift said.  I was at that same convention and the demonstration really did open a lot of eyes for those in the audience that had never seen head welding done.  “I had no idea that heat welding required very specific tools and a skilled, trained mechanic with steady hands,” Swift continued. ‘It just goes to show how important practical field demonstrations are to sales and installation managers working for commercial flooring contractors.” Couldn’t have said it better myself.