Vinyl plank and laminate floors look tough, and in many St. Louis homes they handle everyday spills well. The weak point is rarely the top surface. Water tends to get in along the edges, seams, and transitions, then sits where you cannot see it. This guide walks through what to check and what to do next.
Why the edges matter
Laminate has a fiber core that swells when it stays wet, and that swelling shows up first at the seams and along the perimeter. Luxury vinyl plank is more water resistant at the surface, but its seams still let liquid through, and the subfloor beneath can take on moisture. Either way, the damage is usually hidden until a board lifts, a seam opens, or a smell starts.
Humid St. Louis summers add a slower problem. Moist air moving through a basement or crawl space can raise moisture levels under a ground floor, and a floor that looks fine on top can be damp underneath. Homes with slab floors and older homes with basements both deserve a closer look.
Signs to check this week
- Boards that cup, with edges higher than the center, or seams that have opened into visible gaps
- Soft or springy spots, or a floor that shifts underfoot
- Dark staining or discoloration along baseboards, door trim, and the bottom of cabinets
- Raised or buckled planks near exterior doors, sliding doors, and sunrooms
- A musty smell that is strongest near the floor
- Gaps at thresholds or transitions where one floor meets carpet, tile, or hardwood
Find the likely sources
Most moisture under a floor comes from a few places. Start with the room itself, then work outward.
- Dishwasher and refrigerator water lines, plus any slow drip at the ice maker or under the sink
- Pet accidents, mopping with too much water, or plant pots set directly on the floor
- Exterior doors, where rain or wet boots can seep past worn weatherstripping
- The room below, if the floor sits over a basement or crawl space with damp air or seepage
- Shower or tub edges with failed caulk, if the flooring runs close to wet areas
Simple checks you can do
Lay a dry towel on the floor overnight in a suspect spot, then lift it and look for darkness or a damp feel on the floor surface. Carefully remove a baseboard or transition strip to look at the underside of the flooring edge, watching for swelling, staining, or softness. A basic moisture meter from a hardware store can compare readings across the room. A reading that is noticeably higher in one spot than the rest tells you where to look next. Do not rely on a single reading. Check the same spot at different times of day, because room humidity changes with the weather and with the HVAC system running.
What to do next
Dry a wet area quickly with fans and moving air, but do not flood it with heat. Wipe spills right away. Fix the water source first, whether that is a leaking supply line, a worn door sweep, or an overflowing drain pan. Replacing a single damaged plank is sometimes possible, but only after the moisture source is stopped and the subfloor is dry. If the subfloor is soft, staining runs deep, or there is visible growth on the underside, have a qualified local contractor inspect it before you cover it up again.
Keeping the floor dry long term
Keep indoor humidity steady through the summer, run the air conditioning, and check that condensate drains are clear. Put a mat at each exterior door and use a room gauge to watch the trend over time. If the basement or crawl space below the floor is damp, address that first, since a drier space below helps the floor above. When a repair is already open, ask for a moisture check too, because it is easier to find a problem while the floor is up than after a new floor has already failed.