Heat Welding Linoleum Floors
August 19, 2008
With the increasing awareness of “green” building practices, the use of flooring made from sustainable, renewable products, such as linoleum continues to grow. Linoleum is composed of mainly natural products such as linseed oil, cork flour, wood flour, pine resin and jute backing. These differences will affect installation and maintenance recommendations; failure to understand and follow these recommendations can lead to expensive and unpleasant results.
Heat welding of linoleum is the popular seam treatment for commercial settings, where the majority of linoleum is specified and installed. The tools and techniques for heat welding linoleum are similar for heat welding sheet vinyl flooring; however there are some distinct differences.
One of the greatest differences between welding sheet vinyl and linoleum is the welding rod or thread. Welding rod for sheet vinyl is made from PVC and will not bond to the natural ingredients in linoleum. Linoleum welding rod is made from a thermal plastic material similar to a hot melt glue stick. The difference in the two welding rods is easily identifiable by trying to break a small piece of each by hand. The PVC welding rod will stretch, while the linoleum rod will break easily.
Because of this difference, most linoleum manufacturers recommend heat welding at lower temperatures than sheet vinyl flooring to avoid melting the linoleum welding rod into a liquid, and to prevent discoloring the linoleum flooring at the seam.
The first step to a quality heat welded seam is a well cut, well bonded seam. Be sure to follow manufacturer’s recommendations for seam cutting, and the amount of time needed after adhering the linoleum for the adhesive to set before heat welding. The time will vary from 10 to 24 hours depending on the manufacturer.
With linoleum it is important not to cut the seams too tight; linoleum has a tendency to grow slightly in the width and to shrink slightly in the length. Leaving a slight gap in the seam (not more than 1/64”) will accommodate the growth in the linoleum and provide a track for rolling groovers.
Proper grooving of the seam is critical to a successful weld; the groove must be centered on the seam, of the proper width for the welding rod, and grooved to the correct depth of at least 2/3 of the thickness of the linoleum. For example most manufacturers recommend grooving 2mm and 2.5mm linoleum down to the top of the jute backing. This will provide a good surface for the welding rod to bond with. A groove that is too shallow will result in the welding rod pulling out when trimmed.
The tools used for grooving range from hand groovers to electric and manual rolling groovers. Hand groovers will work on short seams, however they can be difficult to use as linoleum chips can clog the blades, preheating the seams with a heat gun can help to prevent this but generally it is impractical to hand groove long seams.
Electric groovers will work well on linoleum providing they are well maintained with a sharp blade (to avoid chipping the edges of the groove) Complications can be encountered if the groover does not have a “floating base” or the ability to adjust to deviations in substrate flatness. Nothing is harder on a grooving blade than cutting into a concrete substrate. Also a functioning dust bag is critical to good indoor air quality on the job.
Non-electric rolling groovers like the new Marmo Groovers work very well, even accommodating curves and circles. (See Photo 1) Some rolling groovers will require preheating the seam to prevent the blade from clogging; sharp blades are a must to prevent chipping the groove edges.
Marmo groovers, recently introduced to the market have a unique patented design which does not require pre-heating and consistently groove to the jute backing regardless of deviations in floor flatness. They will not chip the groove edges and their special design will not clog. They create no dust makes no noise and can accurately groove to the jute backing in two passes. (See Photos 2, 2A, 3, and 3A)
Whether using an automatic welder or a hand held welder; welding linoleum requires the correct temperature and using slight pressure at the tip to force the melted weld rod into the groove. Welding at a consistent, steady pace down the seam is critical to a solid, strong seam.
Moving too slow will produce a charring of the linoleum, a brown to black color at the seam. Moving too quickly or inconsistently will produce a “cold weld” or “cold spots” that will result in the welding rod pulling out of the seam when skived or trimmed.
Skiving is the processes of trimming the weld rod flush to the surface of the linoleum. Traditional skiving tools are quarter moon or spatula knives and a trim plate. Skiving should be done in two passes, unless using a one pass tool as shown here. (See Photo 5)
The first pass removes the top half of the weld rod decreasing the resistance on the blade when making the final pass flush to the linoleum surface.
Linoleum manufacturers recommend making the first pass while the rod is still warm, if the first pass is made after the rod has cooled any area of the welded seam that is not well bonded will release and the weld rod will pull out of the groove. It is not uncommon to see an installer following the welder making the first skiving pass.
Once the first pass is made, allow the weld to cool completely before making the final pass. Making the final pass too soon can cause the seam weld to be concave, which can lead to unsightly dirt buildup from normal foot traffic. Skiving too soon can also cause the skive knife to dig into the surface of the warm linoleum; it can also leave small amounts of weld rod on either side of the seam, requiring extra work to remove.
To get a clean final skive; allow the weld rod to cool completely. Newer planning systems replace the traditional two pass method, skiving the weld rod in one pass. Adjusting the plane leaves a smooth and flush finish every time. (See Photos 4 and 5)
Once the welded seam is completed, some manufacturers recommend applying a coat of commercial floor polish over the weld to help keep it clean until the floor receives protective maintenance.
With recent improvements in heat welding tools it is easier than ever to weld linoleum with greater consistency, whether straight or radius seams.