In this issue Denver Coleman identifies the challenges one faces when it comes to welding.
With more than 50 years’ experience in the local and international flooring industry, Denver Coleman, Chairman of Polyflor SA, answers questions posed by installers, architects and readers. In this issue he discusses the numerous challenges when it comes to welding, which have been revealed in several vinyl floor sheeting installations.
“I was recently privileged to be one of the judges of the installations in our In Search of Excellence competition,” says Denver. “One of the things that stood out above all other factors was the often poor quality of the welding that was evident in many vinyl floor sheeting installations. I would therefore like to reinforce the key rules for creating a good strong weld with vinyl floor sheeting.
DO: Trim off the factory edge of the vinyl floor sheets, as these may not always be square. There are several useful tools for trimming off 5mm easily, giving an accurate, square edge for butt joining the sheets.
DON’T: Skip this step
DO: As per the manufacturer’s data sheets dating back to the 1960s and 70s, ensure that you overlap, scribe and cut (with a hook blade) your sheets to give a tight butt join.
DON’T: Make the mistake of leaving a space the thickness of a matchstick between the sheets. This is incorrect and is a result of bad training which is likely to lead to a badly welded and weak join.
DO: Groove the tight butt join ONLY two-thirds through the sheet with an appropriate grooving tool. In large installations, an electric groover with a 3,5mm blade or grooving tip is best for speed consistency and accuracy. A “P-type” groover is used to hand groove, and is readily available from reliable manufacturers. Blades should be regularly replaced and not re-sharpened. When grooving a good tight butt join, a steel straight edge is advised to keep the groove straight and prevent veering off into the sheet material.
DON’T: Groove all the way through the material. If you see the screed, you’ve gone too deep. Never use a triangular or similar scraper, as this will open the groove too wide and too deep resulting in a weak weld. Moreover, a groove that is too wide will result in dirt buildup in the groove, as dirt and grit tend to stick and get trapped, further aggravating the situation.
DO: Ensure that the welding gun is set at the correct temperature. Be careful to take into account the type of material being welded, as some materials may require a lower temperature so as not to burn the clear wear layer. Also take note of weather temperatures and adjust the welding temperature accordingly. Weld at a suitable speed to ensure a strongly fused join. Use special welding nozzles for PUR-coated products.
DON’T: Hot knife the welds in an effort to close wide gaps. This only superficially closes small gaps and could damage the sheet surface, retaining dirt around the weld, which will be both unsightly and unhygienic. Leaving a gap, or grooving with the incorrect tool such as a triangular scraper, will result in a wide gap and a visible hairline gap on each side of the weld. Dirt will collect in this space which will show up as a thin black line on either side of the weld. Very often the weld will also fail after a period of 6-12 months as it starts to pull apart.
DO: Ensure that you trim your weld twice. Trimming can be done with a sharp, curved-edge spatula. The first trim should be done with a trimming slide under the cutting edge of the spatula, trimming approximately 0,5mm above the sheet. This can be done while the weld is still warm. The second trim should be done with a spatula (without the trimming slide) only once the weld has cooled down. Special trimming tools are available.
DON’T: Do the second trim while the weld is still hot or warm, as this will result in a concave weld, which is a potential dirt trap. Also avoid scraping to achieve a level and flat weld.
DO: Glaze the surface of the weld which will give it a good finish. To do this, slowly pass the welding nozzle approximately 10mm above the completed and trimmed weld until the surface attains a slight shine or glaze. This will also make the floor less dirt-retentive and easier to maintain. Alternatively, apply a layer of sealer with a thin brush over the trimmed weld.