So, Why Did My Heat Weld Fail?
By Ray Thompson, Jr. and Tim Provence, Installation & Technical Services, Armstrong Flooring
The heat welding process arrived in North America in the late 1980s and when done correctly, sheet vinyl seams create an aseptic seam with great integrity. When done incorrectly, seams will begin to separate and/or discolor — especially in traffic areas.
Unfortunately, these issues continue even as heat welding tools improve. Too many heat weld seams fail today. The most common failures we see are: scorching of the flooring at the seams and seam splitting. In some cases, the weld rod can be easily pulled from the groove or there are sections along the seam where the weld rod is missing.
Several commercial sheet vinyl flooring products today come with enhanced factory-applied coatings. These coatings give the customer either polish or no-polish options to maintain their floor. Many customers are choosing the no-polish option, and the results of a floor with scorched or unprotected seams, can be disastrous.
Scorching occurs when the hot air that melts the rod and groove together flows onto the flooring surface at the seam edges. The excess heat distorts or deforms the factory-applied coating.
To mitigate scorching, the installer should use a welding nozzle designed to focus on the rod and groove. Some of these welding nozzles have been around for many years, with newer designs available.
Further, some flooring manufacturers recommend a protective coating be immediately applied to the finished heat weld. This coating helps protect the finished seam from getting dirty prior to polishing the floor, especially if a no-polish maintenance option is selected by the customer. Depending on the traffic and maintenance frequency, this coating may need to be re-applied.
Heat weld seams that are splitting or pulling out are often referred to as cold spots, which means the vinyl welding rod and flooring did not get hot enough to achieve a strong, monolithic bond.
Remember, heat-welded seams are primarily used in aseptic or clean areas to prevent joints where bacteria and pathogens can collect. When seams begin to split or pull out, the integrity of the floor system is compromised. If a seam begins to split or pull out, repair it quickly as maintenance and traffic will make repair more difficult the longer it is left.
Cold spots are caused by using a welding nozzle that puts too much heat on the flooring surface at the seams. While these nozzles may be used on rubber flooring or linoleum, they will scorch a coated sheet vinyl before the rod and groove get hot enough to bond. When/if the installer notices the scorching, they either immediately turn the heat setting on the welder down or speed up. Both reactions may achieve a partial bond — usually the groove is not fully bonded, resulting in a weak seam that breaks down under traffic and maintenance.
Incorrect techniques while using a hand-held welder include:
- Moving too fast along the seam, or inconsistent speed (slowing down then speeding up) is often observed as the installer shifts to continue along the seam. A sudden movement leaves sections either not welded or partially welded.
- Not keeping the hand-held welder and nozzle in line with the seam and at the recommended spacing above the groove. This includes tilting the gun, which puts most of the heat on one side of the groove (crowding one side) leaving the opposite side partially heated.
- Holding the welder and nozzle too far above the floor to thoroughly heat the groove.
- The groove in the seam is too shallow or too deep. Proper groove depth of 1/2 to 3/4 the thickness of the product (not counting any backing) is critical to the strength of the finished seam as it assures the maximum surface contact is made between the two sheets welded together.
Contributing to the groove issue is the seam. If the flooring seam is weak, then it will affect the strength of the finished weld. The most common issue here is a large gap in the seams being welded.
Quite a few manufacturers recommend a small gap in the seam, about 1/64“, or the thickness of a business card. This gap is to accommodate the front wheel of a rolling groover. When the gap is wider than the fin on this wheel, the groover will drift side to side, creating an inconsistent groove.
In addition, the two sheets being welded together are farther apart, so the installer is filling a gap with weld rod instead of welding the edges of the two pieces together. Notice the groove in Photo #5 below has a more pronounced groove on one side of this failed heat weld.
Very often on installations, we see the edges of the sheets butted together instead of overlapped and recess scribed to create the seam. While butting the edges speeds up the installation, it’s very difficult to get two sheets to align consistently in a long room especially over a substrate that isn’t flat. The result is a seam with extremely tight sections and gaps well over what`s needed for the groover. Keep in mind if you are recess scribing, the seam and angling the knife when cutting the seam will leave a large gap at the bottom of the seam.
Additional causes of weak heat-welded seams include:
- Adhesive not fully dried under the seam; when heat welding a seam over partially dried adhesive, the heat will cause the residual liquid in the adhesive to vaporize up into the groove preventing thermo-fusion.
- Grooving the seams too long before welding increases the chance the groove can be contaminated prior to welding. The best practice is groove only what you can get welded soon.
- Excessive moisture in the substrate, not using and maintaining the correct trowel notch, exceeding the adhesive working time and cold site conditions affect the adhesive bond weakening seams.
Other factors affecting heat weld seams are not enough or too much heat. This can be due to the installer not adjusting the temperature correctly, cold jobsites or an inadequate/inconsistent power source. For example, installers sharing power sources with other trades. An inconsistent/inadequate power source will affect the performance of the heat welder.
Heat settings: How do you know the setting is right? Of course, start with the manufacturer’s recommendation, but the absolute best way is do test welds on a scrap piece prior to welding the floor seams. Allow the gun to heat up and adjust the heat until a good bond between the weld rod and floor groove is achieved without burning, charring or scorching.
Welding nozzles need to be kept clean during use as residue can build up, preventing the weld rod from flowing through causing it to stretch and burn. Residue build-up on the outside of the nozzle can get into the finished weld leaving black spots.
In summary, installers who heat weld seams in sheet vinyl flooring should make sure they fully understand and follow the manufacturer`s recommendation for the product they are installing and heat welding. Ask yourself:
- Is the flooring well bonded? Seams cut as recommended?
- How long after installation can welding commence?
- Are the grooves centered on the seam and at the recommended depth and width?
- Is the right welding nozzle being used, and have test welds been done to establish the proper temperature and speed?
- Are the seams being skived as recommended?
- Do the seams need a protective coating after welding? What coating should be used and whose responsibility is it to apply?
Heat welding requires practice or time on the tools to become proficient. It`s not necessarily just skill, the skill comes with practice. Know your tools and adjust to the products you are heat welding accordingly.