Resilient Installation Corner: Heat-welding Linoleum Seams
May 28, 2008
Heat welding linoleum is really a misnomer. The reality is a heat bonding system because linoleum does not lend itself to a fusion like a vinyl product does. Installers who are proficient in heat welding vinyl products can have a difficult time with linoleum because of the differences in technique required to weld, trim, and finish the heat-welded seam. The following is a series of illustrations to help you understand the nuances in heat welding linoleum.
The edges of the material to be seamed must be trimmed either by straightedge and trimming or by using an edge trimmer as shown. By trimming the material edges it will yield a better and smoother finished seam. (Photo 1)
After the adhesive is applied the seams should be recess scribed slightly open. The reason for scribing the seams is to get in from the edges of the material, which will yield a better seam. The recess scriber should be set slightly open about the thickness of a business card. This will make the task of grooving much easier. (Photo 2)
After the seam is cut you are ready to cut the groove. With linoleum, the groove must be considerably deeper than a groove in vinyl. With linoleum, the groove should be down to, but not into, the jute backing. The best way to achieve this is to use a power groover, because a hand groover does not lend itself to cutting that deep. With a hand groover, a second pass may be required to obtain the required depth. (Photo 3)
This illustration shows the proper depth for linoleum. Note: at the bottom of the groove you can start to see the jute. Installers say that if you run a screwdriver down the groove you can feel the jute-backing. Failure to reach these depths will yield a weak seam allowing the seam to open along the sides of the weld. (Photo 4)
The next step is to select the type of tip that works best for you; I have found the speed tip works best for my needs. Next, you have to determine the temperature that the heat welder needs to be run at. There are several things to consider when making this decision. Manufacturers recommend temperatures ranging from 750º-850ºF (400º-450ºC). There are other things to consider as well these are as follows:
- Temperature of substrate – concrete is generally colder than wood
- Power source – If you are working from a spider box on a commercial site the power supply may be weak due to the amount of power being used at that source.
- Power cord – if your extension cord is small gauge wire or is very long it will require more power to develop the heat necessary to obtain the temperature necessary. Listen to your heat gun and if it surges you have a poor power source or too long of an extension cord.
- Welding speed – Some installers weld faster than others; this too must be taken into consideration.
Almost immediately, while the rod is still warm you can start the trimming process. In this illustration, just ahead of the trim plate note the overflow (wash) of the rod where it joins the groove. That is an indicator that you have a good weld. The use of the trim plate is imperative as it leaves a uniform amount to trim with the final skive. (Photo 6)
The second (final) skive should be done soon after the trim pass is completed. The key to the final pass is a sharp skive knife and one continuous smooth pass. Installers need to, with practice, find the cutting angle that works best for them. Each installer should own and know how sharpen their knife. Using someone else’s tool generally does not work well. (Photo 7)
The completed seam - the final skive is flush with the material, helped by trimming off both edges of the material, a two pass skiving system and the final smooth continuous pass. Some manufacturers recommend a floor polish be applied to the welded seam rod to keep it free from soil and discoloration. I think it is worth the effort. (Photo 8)
As I indicated in the beginning of this article there is a considerable difference between heat welding linoleum and vinyl. With linoleum installers will experience a “zippering” or the weld rod with linoleum that they do not with vinyl, this is because it is a bond and not a weld. The weld of linoleum will get stronger as the material cools and the oils re-solidify.