Guide

Mold Under Carpet, Laminate and Hardwood

The padding is the problem, not the carpet

Carpet padding is open-cell foam or bonded fibre designed to compress and recover. That structure is excellent at holding water and terrible at releasing it, and it sits directly against a subfloor with a carpet on top acting as a lid. A padding that felt damp on Monday is still damp inside on Friday while the carpet face feels dry to a bare foot.

It is also the cheapest part of the floor. Replacing padding across a room costs a fraction of replacing the carpet, and a fraction again of replacing a subfloor. After any water event of consequence, pulling the padding is the single highest-value thing a homeowner can do in the first day.

What survives and what does not

Material	After clean water, caught fast	After days, or dirty water
Carpet padding	Discard. Always	Discard
Carpet	Often salvageable, dried in place or lifted	Discard
Laminate	Sometimes, if the core has not swelled	Discard
Engineered wood	Depends on the wear layer and glue line	Usually discard
Solid hardwood	Often salvageable, may cup then flatten as it dries	Depends, sometimes sanded and refinished
Vinyl plank and sheet vinyl	The material itself is fine. The problem is water trapped underneath it	Lift to dry the subfloor
Ceramic tile	Fine. Check the substrate and grout	Fine, unless the substrate failed
Plywood subfloor	Usually dries and stays	Depends on delamination
OSB subfloor	Swells at the edges, often recovers poorly	Frequently replaced

The trap with vinyl and sealed floors

Sheet vinyl and glued vinyl plank are close to waterproof, which sounds like good news and is not. Water that gets underneath, from an edge, a seam, or from below, cannot evaporate upward through the floor. It sits on the subfloor in the dark indefinitely.

The same logic applies to a basement slab with vinyl over it and no vapour barrier beneath. The slab passes moisture upward continuously, the vinyl stops it, and the adhesive layer and the underside of the plank become the growth surface. A floor that smells but shows nothing is often this.

Checking without demolition

1. Walk it barefoot. Cold spots, soft spots and any give underfoot are worth marking
2. Moisture meter across the surface, comparing against a known-dry part of the same floor
3. Lift a corner of carpet at the tack strip, near a wall, and feel the padding underneath rather than the carpet
4. Pull one length of shoe moulding and look at the bottom edge of the baseboard and the floor perimeter
5. Look at the underside from a basement or crawlspace if the floor is accessible from below. This is the best view available and costs nothing
6. Check where furniture has sat, since evaporation is slowest there
7. Check the closet in that room, which is the least ventilated part of it

Hardwood specifically

Solid hardwood reacts to water in a predictable sequence. First it cups, with the edges of each board rising above the centre, because the underside has absorbed more than the finished top. If it dries evenly it often flattens out again, sometimes over weeks, and may only need sanding and refinishing.

If it stays wet it crowns instead, with the centre higher than the edges, and that generally does not recover. Boards that have separated from the subfloor, or a subfloor that stayed wet under them, are a different job again.

The critical decision is early and counterintuitive: do not rush the drying with heat. Forcing the surface dry while the underside is still wet is what produces permanent distortion. Steady airflow and dehumidification beats a heater.

What to do in the first two days

1. Extract standing water with a wet vacuum
2. Pull and discard the padding. Do not try to dry it
3. Lift furniture off the floor, or put foil or blocks under the legs so finishes do not bleed
4. Remove shoe moulding so the floor perimeter can breathe
5. Run airflow and a dehumidifier together, not fans alone
6. Keep windows shut if it is humid outside
7. Verify with a meter rather than by touch before putting anything back

The window matters more than anything else here. Full detail on mold after flooding, and on what happens when it was not caught in time, mold after a leak.

Common questions

Can carpet be saved after a flood?

After clean water caught quickly, often yes, with the padding discarded and replaced. After gray or black water, or after sitting more than about two days, the carpet goes too. See mold after flooding for the water categories.

My laminate is buckling. Is that mold?

Buckling is the fibreboard core swelling from water, which is a separate problem from mold but arrives with it. Once a laminate core has swelled it does not recover, so that section is replaced regardless.

How do I check under the floor without pulling it up?

A moisture meter on the surface, compared against a known-dry area of the same floor, plus a look at the edges. Lift a corner of carpet at the tack strip, or pull one piece of shoe moulding and look at the bottom of the baseboard.