SW-04 · Troubleshooting & RepairsMost open seams on vinyl plank trace to temperature. Shaw measured a 48-inch plank shrinking by 1/16 of an inch when cooled, and a floor installed warm can open its joints when it cools.1 A pinned floor makes it worse, because the planks separate in the field instead of moving at the walls.1 Joints that were never fully locked and uneven subfloors are the other usual causes.2
A vinyl plank floor goes down tight. Weeks or months later, thin dark lines appear at the short ends of some planks, or a long seam opens along a row. The owner sees a defect. The installer sees a callback. Before anyone touches the floor, it helps to know what opens a seam, because the fix for one cause does nothing for another.
Temperature is the first suspect
Vinyl is stable with humidity but not with heat. Shaw's builder division puts it simply: the plank grows when it is warm and shrinks when it is cool.1 In its test, a plank that was true to spec at 48 inches long shrank by 1/16 of an inch when cooled to 32.2 degrees.1 Heated to 135 degrees, the same plank grew by 1/16 of an inch.1
Shaw gives a direct example of what that does to a floor. If a plank is installed at 90 degrees and then cools to 65 degrees, slight gaps may show on a glue-down floor, and a floating floor may pull away from its edges.1 It names temperature as the primary cause of peaking, gapping, lifting planks and adhesive release.1 Its stable range for the plank is 60-80 degrees.1
The pattern helps confirm it. Gaps that appear in the cold months and close again in summer, or that open near a door or window that is often left open, point to temperature. So do gaps in a floor that was installed before the building's heating and cooling were running.
A pinned floor separates in the field
A floating floor moves as one sheet. When something holds part of it down, the movement has to go somewhere else. Shaw says that if a floor is pinned by a trim fastener, or anything that impedes expansion and contraction, planks may separate in the field of the floor.1 Gaps in the middle of a room, rather than at the walls, are the sign.
The usual pins are cabinets, islands, nailed trim and transition strips fastened through the planks. Timeless Designs says cabinets, heavy furnishings, fireplaces and other built-ins must not be installed on top of its floating floor, because they restrict its ability to expand.2 National Flooring Products warns that heavy furniture of 500 pounds or more may obstruct a floated floor's natural movement, which can lead to buckling or separation.3 The fix is to find the pin and free it: undercut the trim, cut the fastener, or re-set the cabinet so it stands beside the floor rather than on it. See expansion gaps and pinch points.
Joints that were never fully locked
A click joint can look closed and still not be engaged. National Flooring Products says so directly: visually, a row can appear to be engaged but is not.3 It asks installers to tap the short side and then the long side together with an approved tapping block.3 Timeless lists the result of improper locking: distressed joints with a peaked appearance, separation of joints from normal temperature changes, cupping and side joint failures.2
Daltile's sequence for its rigid click plank is to tap the long side joint closed first, then the end joint.4 Marquis asks installers to press down on top of each short end joint to ensure a good connection.5 Seams that open within days, in a floor that has not seen a temperature swing, usually trace back here. Partly engaged joints do not hold the floor together when it moves.
Uneven subfloors stress the lock
A floating plank bridges small dips, but every dip loads the joint above it. Timeless warns that failure to level the subfloor to its specification can put additional stress on the tongue and groove, resulting in plank separation.2 Its tolerance is 1/8 inch in 10 feet.2 The giveaway is a gap that opens over a low spot, often with a hollow sound or a slight rock when stepped on. Fixing it means lifting the planks back to the area and filling the dip. Retightening the joint without fixing the dip does not last. See the flatness guide.
Sun and heat in one area
Sunlit floor runs much hotter than the floor beside it. Shaw notes that temperatures in exposed areas can run in excess of 130 degrees.1 A plank that expands in the sun and contracts at night works its joints every day. Timeless excludes side and end joint gapping from heat or sunlight exposure from its limited warranty.2 Marquis asks for blinds or shades to be closed during peak sun to prevent thermal expansion.5 Gaps clustered by a glass door or south window are the pattern.
Telling the causes apart
| What you see | Likely cause | First check |
|---|---|---|
| Gaps across the floor in cold weather | Temperature shrinkage | Install temperature, HVAC records |
| Gaps in the middle, walls tight | Pinned floor | Cabinets, trim, fasteners |
| Gaps within days, no weather change | Joints not fully engaged | Tap the joint; does it close? |
| Gap over a dip, plank rocks | Uneven subfloor | Straightedge on the substrate |
| Gaps near glass, worse in afternoons | Sun heating | Surface temperature at peak sun |
Closing a gap
When the joint is undamaged and the cause is fixed, a gap in a floating floor can often be closed by working the planks back together. EverStep's method for gaps uses a scrap of plank locked into the plank to be moved, then tapped lightly on its edge.6 That keeps the force off the plank's own profile. Timeless warns never to strike planks directly, because that can fracture the locking system and lead to end joint failure.2 Work from the gap back toward the wall, and keep the expansion space at the far side.
If a joint has broken, closing it will not hold. The plank has to be replaced; see replacing a single plank.
Warranty and commercial floors
Gapping is mostly excluded from coverage. Timeless lists gapping, shrinkage and subfloor-related issues as not covered by its warranty.2 That makes the site conditions the contractor's protection. On commercial jobs, record the floor temperature at installation and confirm that the HVAC is running. Note the fixed objects too, and keep the record. In a building that is unheated over weekends or holidays, consider whether a glue-down product suits it better than a floating one.
Sources
- Shaw Floors, “LVP Case Study: How Temperature Affects Dimension”. shawfloors-sherwinwilliams.com/SiteFiles/sherwinwilliamsdigital/Images/L
- Timeless Designs, “Click Floating Luxury Vinyl Installation Instructions”. timelessdesignsflooring.com/wp-content/uploads/2023/05/TD-Rigid-Core-Ins
- NFP, “Architect’s Choice LVP Installation Guide”. my-nfp.com/resource/architects-choice-lvp-installation-guide
- Daltile, “ProSeries Luxury Vinyl Flooring Installation & Care Guide (Rigid Core Click, Glue Down)”. s1.img-b.com/build.com/mediabase/specifications/daltile/1996309/daltile-
- Marquis Industries, “Rigid Vinyl Plank Installation Instructions (Angle)”. marquisind.com/static/resources/Angle_Angle%20Installation%20Instruction
- EverStep Flooring, “LVP Click Lock Installation Guidelines”. everstepflooring.com/lvp-click-installation-guidelines/
General information for the flooring trade. This article was drafted with AI assistance and checked against the sources listed above; the manufacturer's current instructions and the project specification govern any real job. If something here is wrong or out of date, tell us.
