Water under laminate or vinyl flooring

Signs water is under the floor

Laminate and vinyl plank hide water well. The surface can wipe dry while water sits underneath. Watch for:

• Cupping. The edges of the planks rise higher than the middle.
• Seams that open or lift. Gaps appear between planks, or the joints peak upward.
• Swollen edges. Laminate has a wood-fiber core that swells when it takes on water, and the swelling shows first at the seams.
• Soft or spongy spots, or planks that shift, click or flex underfoot.
• Water squeezing up through the joints when you step on them.
• Dark lines along the seams, or stains and swelling on the baseboards.
• A musty smell near the floor, with nothing visible to explain it.

Vinyl plank is often sold as water-resistant or waterproof. That describes the plank, not the floor under it. Water can still run through the seams and in from the edges, then sit on the underlayment where you can’t see it.

Why water under a floating floor is hard to dry from above

Most laminate and many vinyl plank floors are floating floors. The planks lock to each other and rest on a thin underlayment. They aren’t glued or nailed to the floor beneath. Over concrete, installers often add a plastic film to keep moisture from coming up from the slab.

That design works against drying:

• The planks block evaporation. The surface layer is made to shed water, so moisture underneath has nowhere to go.
• There’s no air underneath. Water trapped between the plank, the underlayment and the slab sits still. A fan above the floor dries the surface and little else.
• The film traps water from above too. A layer meant to keep slab moisture down also keeps leak water from soaking away.
• Water travels. A floating floor often runs through several rooms without a break, so water can spread under it well past the spot where it got in.

The EPA’s cleanup table is plain about this. For vinyl and other hard flooring, it says to “Check to make sure underflooring is dry; dry underflooring if necessary.” A footnote adds that the subfloor under carpet “or other flooring material must also be cleaned and dried.” The table is written for clean water and a response within 24 to 48 hours, the window the EPA gives for drying materials to prevent mold.

What’s under the planks in most Valley homes

In most Valley homes, the answer is a concrete slab. University of Arizona Cooperative Extension says floating and monolithic slabs are the most common foundation types in Arizona.

Concrete matters for two reasons:

• It holds water and gives it back slowly. For concrete, the EPA’s table says to remove the water with an extraction vacuum and speed drying with dehumidifiers, fans or heaters. A covered slab dries much more slowly than an open one.
• New flooring shouldn’t go down on a wet slab. Flooring makers generally set moisture limits for the concrete before installation. The provider’s readings show when the slab is ready.

Upstairs floors and some homes have a wood subfloor instead. The EPA says wet wood should have moisture removed right away and be dried with dehumidifiers, gentle heat and fans. Wood subfloors can swell and need checking for mold on the underside.

Could the water be coming from under the slab?

If no appliance overflowed and no pipe burst, the water may be coming from below. Pipes run under or through the slab in many Valley homes. The Smart Home Water Guide, published with the City of Phoenix, suggests feeling for hot spots on the floor after running hot water at nearby fixtures, since a warm patch could indicate a leaking hot water pipe under the slab. It notes that most interior pipe leaks happen on hot water lines.

Other common sources of water under a floating floor:

• Dishwashers, refrigerator icemaker lines and washers, which can leak slowly out of sight.
• Water heaters that sit inside the house rather than in the garage. Our guide to a water heater leaking from the bottom covers what to do first.
• Toilet supply lines and the seal at the base of a toilet.
• The sink cabinet, where a slow drip runs under the cabinet and out beneath the flooring.
• AC condensate. ENERGY STAR warns that a plugged condensate drain can cause water damage in the house.
• Rainwater or runoff that came in under an exterior door.

Your water meter can help. Our guide to checking for a hidden water leak walks through the test. A plumber or leak detection specialist confirms and repairs a leak under the slab. The flooring and the slab it soaked are a separate job: see slab leak water damage.

What a restoration provider checks

Expect the provider to measure before deciding what comes up:

• The whole floor, not just the wet spot. A pinless moisture meter can scan through many planks without damaging them, and a thermal camera can point to cooler, damp areas. Readings are compared with the same flooring in a dry part of the house.
• Seams and edges. Water often shows first along the joints and at the walls.
• Baseboards and the bottom of the drywall. Water under the floor wicks into both.
• Cabinet bases and toe kicks. In kitchens and bathrooms, the floor often runs up to or under the cabinets, and water collects there.
• The slab itself, once planks are lifted. That reading decides how long drying will take and when new flooring can go down.
• The type of water. Water from a toilet bowl, a drain or outside is treated as contaminated, which changes what can be kept. Porous layers like foam underlayment usually come out. See emergency water extraction for how standing and contaminated water are handled.

Older homes need one more check. Some floating floors were laid over older flooring. The EPA lists vinyl floor tiles, the backing on vinyl sheet flooring and some adhesives among materials that may contain asbestos, and says testing is the only way to know. If you find older flooring under the planks, leave it alone and tell the provider.

Removal, drying and the floor that comes next

Laminate that has swollen is usually a loss. Vinyl plank holds up better, but the planks often have to come up anyway so the slab can dry. Once the floor is open, the provider:

1. Removes the wet underlayment. Like carpet pad, it’s rarely worth drying.
2. Dries the slab with dehumidifiers and air movers, taking readings each day until the concrete reaches its dry goal. Our guide on how long water damage takes to dry explains why concrete is slow.
3. Dries the walls and cabinets the water reached. See structural drying.
4. Checks for mold on the underside of planks, the underlayment and the lower walls.

Replacing the floor is a separate job. A flooring installer puts in the new floor once the readings say the slab is dry. Some restoration providers also handle rebuilds, and many don’t, so ask which kind you’re talking to.

What to do first

1. Stop the water at the fixture’s valve or the main shut-off. The plumber or appliance technician handles the repair.
2. Photograph the floor: cupped planks, open seams, stained baseboards and the source. If you have leftover planks or boxes from the install, keep them. The product name helps with matching and with an insurance claim.
3. Move furniture and rugs off the affected area.
4. Don’t pull up planks in an older home before anyone knows what’s underneath.
5. Call a restoration provider to map the wet area and start drying within the 24 to 48 hour window.

Before work starts, look up the contractor’s license with the Arizona Registrar of Contractors and get the scope of work in writing.