How to Heat Weld a Seam in Commercial Sheet Flooring

Why this matters

In a clinic, a school kitchen or a lab, a seam in sheet flooring is the one place water, cleaning chemicals and dirt can get into the floor. A heat-welded seam closes it by melting a rod of the same family of material into a groove cut along the seam, so the floor becomes one continuous surface that can be mopped and disinfected. A weld that looks fine and has a void underneath, or that was skived flush while hot and cooled into a shallow trough, fails at exactly the job it was specified for. Specifiers and facility managers inspect these seams; many will reject a corridor over one bad run. Why commercial specs ask for this and what else changes on those jobs is in Commercial Flooring: What Changes From Residential.

Start state

• Seam adhered and rolled. Both sheets fully adhered under the seam, rolled with the roller the maker names, edges tight with no gap and no overlap. A weld bridges nothing; it seals a closed seam.
• Adhesive set. Grooving pulls on the sheet edges. Wait the time the flooring maker states before grooving, often the next day for full-spread adhesives; grooving into soft adhesive drags the edges and tears the bond.
• Rod matched to the floor. The maker supplies or names a rod for each product and color. Vinyl rod and linoleum rod are different materials with different temperatures; never mix them.
• Tools: a power or hand groover with a depth setting, a hot-air hand welder with the speed nozzle for that rod's diameter, a spatula or quarter-moon skiving knife, the trimming plate (a slotted guide that sets the first-pass height), a scrap of the same flooring for a test weld, and a vacuum.
• Ventilation in the space, and nothing flammable near the welder.

Step 1: Groove the seam

Set the groover's depth to the figure the flooring maker states, commonly about two thirds of the sheet's thickness, and the groove width to match the rod. Run it centered on the seam in one steady pass, guided along the seam line.

Why that depth: too shallow and the rod has too little material to fuse into, so it sits on the surface and can peel; too deep and the groove cuts into the backing or the adhesive line, which weakens the sheet edges and can let the rod bond to adhesive instead of flooring.

What wrong looks like: a groove that wanders off the seam leaves one edge uncut, so the seam line shows beside the weld. Re-groove by hand along that stretch.

Vacuum the groove clean. Adhesive crumbs and dust in the groove become voids in the weld.

Hazard: a power groover's blade is exposed at the base; keep fingers off the line ahead of it and unplug it to change or adjust the blade.

Step 2: Preheat and test on scrap

Set the welder's temperature to the rod maker's figure for that rod, fit the speed nozzle, and let the tool warm for the time its maker gives; air temperature drifts until it stabilizes. Groove a strip of scrap to the same depth and weld 2 or 3 ft of it.

Look at the test weld: a small, even bead of melted material along both edges of the groove, and no shine of scorching or discoloration. Let it cool and try to lift the rod's end with a fingernail; a good weld will not peel.

Hazard: the nozzle and the air leaving it are hot enough to burn skin through a glove and to scorch flooring in seconds. Never set the welder down nozzle-first; use its stand. Overheated vinyl gives off hydrogen chloride and other irritant fumes, and the scorch mark is the sign it happened: stop, lower the temperature, and keep the space ventilated. Linoleum scorches too, with its own fumes.

Step 3: Weld the run at a steady speed

Feed the rod into the speed nozzle, start at one end of the seam, and draw the welder along the groove with the nozzle angled as its maker shows, letting the hot air melt both the rod and the groove walls together. Speed is the variable you control:

• Too fast: the rod is pressed in but not fused. It looks fine on top and peels later.
• Too slow: the rod and the sheet edges scorch, and the bead spreads wide.
• Right: an even bead along both sides of the rod for the whole run.

At a restart or where two runs meet, cut the old rod's end on a long taper and overlap the new rod onto it so the joint fuses, never butt two ends.

Ends at walls, door frames and casework. A power groover stops short of a wall by the width of its own housing, which leaves the last few inches of every seam ungrooved. Finish those inches with a hand groover at the same depth before welding, then weld the run all the way into the corner, leaning the nozzle so the hot air reaches the end of the groove. An end left ungrooved and welded over looks closed for a week; it is the stretch where the rod lifts first, because it is sitting on the surface rather than fused into a groove, and it is next to the wall where the mop water collects.

Step 4: First skive, while the rod is warm

Within the time the rod stays warm, set the trimming plate over the rod and draw the skiving knife along the plate. The plate holds the blade above the floor so it takes off most of the bead and leaves a thin crown standing above the surface.

Why not flush now: hot rod is expanded. Cut flush while hot, and as it cools it shrinks below the floor surface into a shallow trough along the seam that holds dirt and shows as a dark line.

Step 5: Second skive, when the rod is cool

When the rod has cooled to room temperature, take off the remaining crown with the skiving knife held flat on the floor, cutting in long, even strokes until the weld is flush with the sheet.

Hazard: a skiving knife is sharp enough to cut through a glove; draw it away from your body and keep the other hand behind the blade. Cut-resistant gloves on the holding hand are cheap insurance.

 SECTION through one seam, not to scale
 1. GROOVED, rod held above it
                     (O)   weld rod
 sheet A ----------\     /---------- sheet B
                    \___/  groove about 2/3 of
 adhesive ==========seam==========  sheet depth
 2. WELDED: groove full, bead stands proud
                    /^^^^\
 sheet A ----------+-----+---------- sheet B
 3. SKIVE PASS 1, warm, over trimming plate
                    _____   thin crown left
 sheet A ----------+-----+---------- sheet B
 4. SKIVE PASS 2, cool, knife flat on sheet
 sheet A ----------+-----+---------- sheet B
                    flush, no crown, no dip

Worked example: a clinic corridor

The floor: a homogeneous vinyl sheet 2.0 mm thick in a clinic corridor 40 ft long, with one seam down its length. The maker's sheet calls for a groove two thirds of the thickness and a 4 mm rod of the matching color, and for grooving no sooner than the morning after installation.

Groove depth: two thirds of 2.0 mm is about 1.3 mm. The crew set the groover to that, then checked it on scrap with a depth gauge before touching the corridor: 1.3 mm.

Welding: the test weld on scrap peeled at one end with a fingernail. The installer had been moving fast to beat a nurse shift change. Slowed down, the second test held. The 40 ft run went in as two 20 ft runs with a tapered overlap at the middle, because the rod coil on hand would not do 40 ft in one length.

The problem found: after the second skive, a 3 inch stretch at the overlap showed a hairline down the center of the weld: the overlap had not fused, because the second run did not dwell long enough at its start to reheat the cold, tapered end the first run had left. The crew re-grooved that 3 inches by hand, about an inch past each end of the hairline, welded a short length of new rod with a tapered start and finish, and skived it in the same two passes.

Result: a 40 ft seam, flush, one repaired section about 5 inches long including its tapers, signed off by the facility's representative on the walk.

How to verify you got this right

• Flush. Run a fingertip across the weld at several points: no ridge, no dip. Then look along the seam standing, in normal light, toward the corridor's windows or lights. A trough shows as a darker line.
• Continuous. Walk the whole seam looking for hairlines down the center of the rod, unfused edges, or pits. Pay most attention at overlaps, restarts and the ends at walls.
• No voids. A void can hide under a good-looking skive; pressing a fingernail along the edge of the weld at overlaps and ends finds a rod edge that lifts.
• No scorching. Brown or shiny stretches mean the weld ran too hot or too slow there. A scorched weld is cut out and redone, because scorched material is brittle.
• Record it. Note the rod lot, the temperature setting, the groove depth and any repaired sections with their locations on the job sheet. A facility that inspects seams asks.

What changes the call

• Linoleum welds with linoleum rod at its own temperature and is skived in the same two passes; its rod is less forgiving of re-heating, so repairs often mean cutting out a longer section.
• Cold-weld or chemical seam systems are a different method used on some residential and light commercial products; they are not a substitute where the specification calls for heat welding.
• Flash cove, where the sheet runs up the wall as an integral base, adds inside and outside corners that are welded the same way but by hand in tight space; plan the rod and the nozzle for them before the day.

References

• The flooring maker's installation instructions (groove depth, rod, wait time before grooving, welding temperature)
• The welding tool maker's operating instructions and the rod's SDS
• See related: Commercial Flooring: What Changes From Residential
• See related: The Commercial Flooring Coordination SOP