The weld did not adhere to one side of this sheet vinyl seam. This could be caused by a poorly grooved seam, too low a temperature on the heat gun, or moving too fast when welding. Photo courtesy of Mark Violand

Seams in floor coverings – whether we’re talking about carpet, resilient or tile – cause more concern for customers and more potential complaints for dealers and installers than any other aspect of a floor covering installation.  In my career as a retailer and an architectural sales rep, I can’t count how many questions I have had to field about seams.  Where will they be?  Will they show? Will they last?  Whether it’s a homeowner, an interior designer, architect or property manager, it is a common concern. Seams are probably where I have seen the most disappointment among consumers in all types of floor covering products. 

Grout problems nag tile installers and VCT seams often wind up showing as floors get older.  A retail salesperson describes a carpet as “seam hiding,” an architectural rep makes the same clam about heat welding rods, or someone claims that carpet or resilient tile products are cut so well that the floor will look “seamless.” Statements such as these put a lot of pressure on the installer, when in fact the product itself, even with the best installer working with it, may not be able to deliver on these promises.  Every carpet shows seams to a certain degree, and even “camouflage” heat weld rods are noticeable. In both cases, the light shining into a room may have an impact so that the seam is not noticeable from one angle and may be more noticeable from another side.   As far as tile seams, they may look great on a new floor, but as time goes on and the floor is cleaned, chances are they will start to show after a while, especially in light colors. 

As an inspector and an instructor of the IICRC (Institute of Inspection, Cleaning and restoration Certification) Resilient Floor Inspector course, a lot of time is spent diagnosing seam failures in resilient sheet flooring – whether the seams are heat welded or sealed with a liquid seam sealer.  So here are a few key points for seam success.

Communication and Planning

Operating at too slow a speed or at too high of a temperature causes damage on the surface of the flooring material, as shown in this photograph. Photo courtesy of Mark Violand

A lot of the success of any given floor covering installation has to do with communication on the sales and specification side – making sure the owner knows what is coming on all aspects of the installation from substrate testing and preparation to furniture moving, protecting the floor after installation and so on.  They need to be told   there will be seams and that you may be able to see them.

Getting seams right and overcoming potential objections from the owner is a team effort between the salespeople, the estimator and the installer, and if there is a designer or architect involved they can be a part if the process as well. People who sell floor covering products could use a little help knowing the limitations of the products they sell so they can be honest with the end user. If the installer has good or bad experiences installing particular products, it helps to get that information back to the sales team so they can sell accordingly.  Perhaps a product that takes longer to install will cost more in order to compensate the installer for the extra time.  Or, if a specific product goes in really nicely, the sales team can “push” that line because a successful installation is a terrific advertisement for future business.  Estimators are a key to communicating site conditions back to the dealer and/or the sales team, so the installer knows what to expect.   It’s all about communication and that is how successful floor covering businesses stay on top.

Seam placement is the first step.  Ideally, seams should be placed in inconspicuous areas, avoiding cross seams, which tend to be more noticeable than length seams. This is where the teamwork comes in because more material may be needed in order to accomplish this.  However, there is often a time savings on the installation and a less noticeable seam if cross seams are minimized or eliminated.  The estimator should not automatically assume that the customer will want to save money by having more cross seams and using less material.  Take a little time to explain the difference and the advantages to the owner and in most cases they will pay a little more to have a better looking installation.  Leftover material may be useful as “attic stock” for future repair work or for other uses, so don’t assume it will be “waste.”

Handling

When it’s done correctly: Properly cut and sealed seams make this custom sheet vinyl installation a thing of beauty. Photo courtesy of Lonseal

Regardless of whether a seam is heat welded, chemically welded or not sealed at all, which is an option on many products, proper handling of the flooring the material before and during the installation is important.  Damaging the edge of a roll can create big problems when making a seam, so from the time they come off the truck until they get installed; the rolls need to be handled gently to prevent damage.  In addition, temperature has an effect on almost any flooring material, so installing very cold or very warm material can lead to problems later on, even if you leave the job with a “perfect” seam.  Because the product can expand or contract due to temperature, every flooring manufacturer recommends acclimation of the material for at least 48 hours.  That means that deliver the product two days before it is to be installed and at that time make sure that the job site is at the proper temperature condition.  Temperature is critical – don’t proceed with installations that have material or site conditions that are not right as far as temperature is concerned.  You can be sure the manufacturer will not be standing behind product failures in such cases, so it falls to the dealer and/or the installer when something goes wrong – and seam failures top the list of temperature-related resilient flooring complaints.

Another important step is trimming the edge of the material.  It may be tempting to use the factory edges if they appear to be straight and clean, especially when heat welding material without a pattern.  However, there may be sections where the material is not 100 percent straight, or there may be contamination that will prevent a good bond so it is imperative to always trim the seam edges.   

Heat Welding

Recess scribing is a common technique for fitting seams. Photo courtesy of Azrock

In commercial resilient sheet goods and tile products, many seams are heat welded to provide a more sanitary installation or meet a building code of some kind.  Health care applications such as hospitals, assisted living facilities, medical offices and so on continue to be the number one area for heat welded seams.  Installers who can heat weld – and do it well - are in demand because health care continues to be a strong market for resilient flooring.

The heat weld seaming process involves routing (also called grooving) at the seam of sheet flooring so that each edge is equally beveled, creating a groove where heat weld rod (also known as heat weld thread) is melted using a hot air gun designed specifically for heat welding. Heat welded seams are recommended for 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. Decorative appearances such as stripes or added color may also be achieved using contrasting heat weld rod.   Generally, routing and heat welding of seams is performed the day after flooring is installed to allow adhesive to dry, although in some cases it can be done the same day.  Check with the flooring manufacturer to be sure.  Welding rods come in a variety of different sizes, so check the specifications of the product you are installing to be sure you don’t rout the seam too wide or too deep and also be sure you have the right tip on the heat weld gun.  For example, if you use a 5-mm tip with a 4-mm weld rod, there will be a problem because of all the extra hot air going through the tip.

Some tile products are routed at the factory, but in most cases routing is done on the job.  Once the groove is routed the heat welding process continues.  The heat welding gun has a range of temperature settings and the setting will vary depending on factors such as the temperature of the room and the substrate and how fast the installer moves the gun.  It is important, even for experienced installers, to practice on some scrap material before welding the seams.  This way the temperature of the gun can be adjusted, because it will not necessarily be the same on every job.

Trimming the edges of the material is important too, although a lot of installers seem to think it is alright to use the factory edge without trimming it.  A clean, freshly cut edge will always make a better seam than a factory edge.  After trimming, the sheets are set in place.  It is often acceptable to leave a small gap at the seam so the welding equipment has a straight line to follow.  This is usually the thickness of a knife blade.  If a wider gap is left, the integrity of the seam may be affected, which is a common mistake. Don’t assume the welding rod will fill in the gap.  The idea is to have welding rod attached to flooring material all the way around, not attached to flooring material on the sides and concrete on the bottom.  That type of seam will never hold.  

Mistakes in heat welding can be avoided by using the proper tools and following the right procedure.  Some of these mistakes are shown in the photographs here. 

• If the tip on the welding gun is wider than the thread or the gun runs too hot or too slowly, the flooring material can be damaged or even burned.

• Since the welding rod expands when it’s hot and returns to its original size when cool, it is important to wait for the rod to cool before doing the final trim.  If the new weld is trimmed before it cools, the weld may be “concave”, creating a dirt trapping “gully” at the seam. 

• If the welding rod does not hold on one side or another the seam can fail.  This can be caused by not centering the groove on the seam cut, running too fast or running too cool.  Any of these factors or a combination can cause the weld not to hold on one or both sides of the seam.   

Mark Violand of D&R Carpet Service of Brooklyn Park Ohio is an experienced inspector and a member of several IICRC Technical committees.  He shared these heat weld photos with us, saying, “This is a welding error, not an installation error or manufacturing defect.  Since the weld did not take on one or more sides of the seam, water penetrated the seam, dissolved the adhesive holding the vinyl to the floor allowing it to curl and shrink.”  Even “automatic” welding equipment can produce seams that have problems such as this, so proper technique is important.  

Chemical Welding

The proper combination of the right tools, the right temperature and the right speed make for a beautiful heat weld seam. Photo courtesy of Azrock

In the case of chemically sealed seams, also called chemical weld, cold weld or seam sealer, a clear adhesive is used to physically glue the two pieces of material together, often leaving a clear bead on the surface.  Most chemically sealed seams are for residential products, although there are a growing number of commercial jobs being done this way.  I have found just as many problems, if not more, with chemically welded seams as there are with heat welded ones.  There are many different methods for chemical seaming, including different types of applicator tips, the use of masking tape on some flooring products to keep the liquid off of the surface, and new “low VOC” products that are coming into the industry today.  When using a product for the first time it is a good idea to learn about it before getting out on the job. Practice using the seam sealing method, call the flooring manufacturer’s technical department or have someone from the manufacturer come out to demonstrate how it works so you are completely comfortable when you go out on the job.  You only get one chance to make a good seam and mistakes are often difficult or impossible to fix!

As I said earlier, it is critical to trim the seam edges.  Depending on the product, seams may be double cut, recess scribed, or “straightedge and butt.”  For chemical weld seams, the sheets material should butt together snugly, but not so tightly that the material “peaks” or “puckers.”  After setting the material into the adhesive and rolling the floor, it’s advisable to wait a few hours for the adhesive to set before sealing the seam. This will prevent wet adhesive from contaminating the seam, which can cause discoloration – a major problem that is not repairable.  This waiting period may be eliminated with different adhesive systems such as “dry lay” adhesives or tape systems, so check with the manufacturer to see what they recommend. When applying the seam sealer liquid, it is important to be sure the applicator tip is inside the seam for the entire length of the seam.  The part of the sealer that counts is what is inside the seam opening, not the coating on top.  I have seen a lot of seams with gaps because the applicator tip skipped a small section of seam, or popped out of the seam and just ran along the surface.

After sealing the seam, be sure the seam is protected so the sealer has enough time to dry.  This can be done by cutting cardboard cores in half to use them as seam covers, using “caution” tape on either side of the seam or any number of other methods.  It’s important to make sure the seam is not disturbed for at least the first hour or so because any damage is difficult if not impossible to repair. 

Chemically welded seams can be exceptionally strong.  I remember in an installation training class I taught when I stood on a two-day-old seam and my students lifted up the flooring with me standing on the seam, which did not budge. I am not a small guy, so this was pretty impressive!   I’ve seen lots of seams last for years and years but I have also seen failures because of improper technique, so take your time!

Training

The material was damaged before installation and did not lay flat, even with a strong adhesive. Always handle rolls carefully and trim the edges so the seam is clean and snug.

No matter how much experience you have as an installer, don’t pass up any opportunities for training if the chance arises.  With all of the new sheet products hitting the market in the past several years, the methods you used to use may not be appropriate any more and new methods may save you time on the job.

Making sure the pattern is matched is another way to prevent complaints about seams. Photo courtesy of Jon Namba

In addition, with the growth in commercial sheet flooring requiring heat welding, several resilient manufacturers offer training in heat welding, so it’s a good idea to invest your time and money into one of the classes if you think you’ll be doing a lot of this kind of work. The knowledge you gain will allow you to increase your income, so the class can pay for itself quickly and you will have a lot more potential work in the future.