Diagnosis

Why floors fail

Start with what you can see. Twenty ways floors and carpets go wrong, each with the mechanism behind it, the standard that governs it, and an honest answer about where the warranty lands.

Most flooring failures are not product failures

Of the twenty failures below, two are primarily about water reaching the material and none are really about the material being defective. What recurs instead is moisture arriving from the building, a substrate that was not flat, stiff or dry enough, movement given nowhere to go, and installation shortcuts.

That is not a defense of manufacturers — it is the reason so many claims are denied, and knowing which category you are in before you make one is worth more than any argument you can have afterwards.

Root causes

The five things that break floors

Moisture Water arriving from below, behind or through — almost always the slab, the crawl space or the seasons. 2 of 20
Movement Everything expands and contracts. Failures happen where it was not given room to. 3 of 20
The substrate Flatness, stiffness and dryness. A floor copies whatever it is laid over. 5 of 20
Installation Tension, trowel, timing and acclimation. Not the product. 4 of 20
Inherent Behaves as designed and is still disappointing. These are the ones warranties exclude. 6 of 20
Diagnose it

Find it by symptom

Filter by what caused it, or read straight through. Every entry names the materials it affects and links to the full guide.

What you are looking at. Each board dishes across its width — run a hand sideways and you feel every edge. Usually worse near a kitchen, bathroom, exterior wall or over a crawl space.

Why it happens. The underside is wetter than the top. Wood swells where the moisture is, so the bottom face grows, the edges lift and the board becomes concave. The source is nearly always beneath the floor — a damp crawl space, a slab still giving up water, a slow leak — not what was spilled on top.

What the standard says. NWFA calls for the interior to be held at 30–50% relative humidity and 60–80 °F. Cupping is a moisture-differential symptom, so the diagnosis starts with a meter, not with the boards.

Where warranties land. Depends entirely on where the water came from. Manufacturer warranties exclude moisture damage from the building, which is most of it. A slab that was never tested to ASTM F2170 before installation is an installation question, not a product one.

A cupped floor often flattens on its own once the moisture differential is gone. That is why the timing of any remedy matters more than the remedy.

How to fix it →

Affects: Solid Hardwood, Engineered Hardwood

What you are looking at. The opposite of cupping — each board is domed, high in the center, with the edges dropping away.

Why it happens. The most common cause is a floor that was cupped and got sanded flat before it had finished drying. Sanding removes the raised edges while the board is still swollen; when the moisture finally equalises the board tries to return to flat, and the material that would have made it flat is now dust in a bag.

What the standard says. NWFA guidance is to return the floor to its normal moisture content and let it flatten before sanding. There is no way to test this by eye — it needs a meter and patience.

Where warranties land. Almost never a product claim. This is a sequencing failure, and a well-documented one.

It is the clearest example on this page of a repair causing the defect.

Affects: Solid Hardwood, Engineered Hardwood

What you are looking at. A run of boards rises off the subfloor, sometimes several inches, often in a tent or a wave across the room.

Why it happens. Wood that has taken on a lot of water expands hard. If it cannot expand sideways — no expansion gap, or trim pinning the perimeter — the only direction left is up. On a floating floor the same thing happens without any flood at all if the gap was never left.

What the standard says. Floating floors need a 1/4"–3/8" expansion gap at every wall and every vertical obstruction, including pipes, door jambs and islands.

Where warranties land. Flood damage is excluded everywhere. A missing expansion gap is an installation defect, and it is visible: lift the shoe molding and look.

This is the failure most often blamed on the product and least often caused by it.

How to fix it →

Affects: Solid Hardwood, Engineered Hardwood, Laminate

What you are looking at. Thin gaps between boards, widest in the driest months, narrowing again when the humidity comes back.

Why it happens. Wood gives up moisture to dry indoor air and shrinks across its width. Wider boards move more than narrow ones, because the same percentage of a bigger number is a bigger number.

What the standard says. Normal within the 30–50% RH band. Gaps that do not close, or that appear at only a few boards, are a different problem.

Where warranties land. Seasonal movement is excluded as a characteristic of the material, not a defect. Engineered wood moves less precisely because its core plies are turned against each other.

The width you choose is a decision about how visible this will be.

How to fix it →

Affects: Solid Hardwood, Engineered Hardwood

What you are looking at. One board or a small patch that talks back every time it is stepped on. It is usually the same spot every time, and pressing down slowly instead of walking across it often makes the noise worse, not better.

Why it happens. This is a subfloor problem wearing a flooring costume, not a wood problem or a carpet problem. Almost always it is friction: a fastener that missed the joist — or one that has since backed out — lets the subfloor flex a fraction of an inch under weight and rub against the fastener shank, or the subfloor itself is deflecting across a joist that is too far away or too far gone. What sits on top only changes how directly you feel it. A nailed hardwood or a floating floor transmits that movement straight up. Carpet and its pad cushion the impact and muffle the sound, which is why carpeted rooms squeak less often — but a genuinely loose connection can still talk through carpet under enough weight, especially right over the worst spot.

What the standard says. NWFA attributes most hardwood squeaks to inadequate fastening into the subfloor rather than to the flooring itself, and calls for re-fastening from above or below rather than replacing boards. The same logic applies regardless of what is on top: fix the connection, not the finish.

Where warranties land. Not a product defect in any case, so the manufacturer will not cover it — but the original installation is squarely at fault, and where a labor warranty exists, it should.

Usually the easiest failure on this page to actually fix — a screw driven into the right spot, not a repair project.

How to fix it →

Affects: Solid Hardwood, Engineered Hardwood, Laminate, Nylon Carpet, Polyester / PET Carpet, Wool Carpet, Olefin (Polypropylene) Carpet, Triexta (PTT) Carpet

What you are looking at. Rolling waves, often parallel to one wall, that reappear within weeks of being walked flat.

Why it happens. The carpet was not stretched tight enough at installation. A knee kicker positions carpet; it does not tension it. Without uniform tension the carpet relaxes and the slack has to go somewhere.

What the standard says. CRI 104 and CRI 105 make a power stretcher mandatory, with roughly 1–1.5% stretch across both length and width. A knee kicker is explicitly a positioning tool, not a stretching one.

Where warranties land. Not a product defect, so the mill will not cover it — but it is squarely an installation defect, and most installation warranties do. Ask who stretched it and with what.

Left alone, ripples abrade at the crests and can delaminate the backing, which turns a re-stretch into a replacement.

How to fix it →

Affects: Nylon Carpet, Polyester / PET Carpet, Wool Carpet, Olefin (Polypropylene) Carpet, Triexta (PTT) Carpet

What you are looking at. Gray or black lines hugging the walls, under doors, along stair edges, and sometimes in straight lines out in the field where subfloor sheets meet.

Why it happens. Air is passing through the carpet at its edges and the pile is doing what a filter does. The fine airborne soil — cooking oils, fireplace and traffic emissions, fine clay — is left behind in the fiber. The carpet is not dirty in the ordinary sense; it has been used as an air filter.

What the standard says. CRI attributes it to airflow through carpet and edges, frequently from an unbalanced HVAC system where more air enters a room than can leave it. Sealing gaps in the subfloor and under baseboards reduces it, as does leaving interior doors open while the system runs.

Where warranties land. Excluded. It is a building-airflow condition, not a carpet condition.

Routinely mistaken for mold or for a cleaning failure. It needs aggressive chemistry and it will come back if the airflow does not change.

Affects: Nylon Carpet, Polyester / PET Carpet, Wool Carpet, Carpet Tile (Modular), Olefin (Polypropylene) Carpet, Triexta (PTT) Carpet

What you are looking at. Irregular areas that read lighter or darker than the rest and appear to move as you change position. They do not follow traffic lanes and they do not vacuum out.

Why it happens. The pile has permanently reversed direction in those areas, so light reflects off the side of the yarn instead of the tip. Nothing is worn, soiled or damaged — you are seeing the same fiber from a different angle.

What the standard says. CRI states that pile reversal is not a manufacturing defect, is unrelated to materials or process, and is difficult if not impossible to predict or prevent. It is most often seen in dense, smooth, plush cut-pile constructions.

Where warranties land. Excluded essentially everywhere, and named explicitly in most warranty documents. It is permanent and there is no accepted correction.

The most disputed carpet complaint there is, and the one where the buyer is most often told something that is technically true and completely unsatisfying.

How to fix it →

Affects: Nylon Carpet, Polyester / PET Carpet, Wool Carpet, Triexta (PTT) Carpet

What you are looking at. The path between doorways loses its texture and reads darker, while the untrodden edges still look new.

Why it happens. The yarn tips have untwisted and splayed. Once the twist is lost the fiber cannot stand back up, and the flattened tips scatter light differently, which is why it reads as a stain that will not clean.

What the standard says. Resilience is a fiber property. Nylon recovers from crushing better than PET, which is most of what the price difference buys. Twist level and density predict this better than face weight does.

Where warranties land. This is the one appearance complaint that texture-retention warranties do cover — but they are written to a defined severity scale and a time limit, and they exclude the pooling and shading above. Read which of the two you have before claiming.

A denser pad does not prevent it. Density in the carpet does.

How to fix it →

Affects: Nylon Carpet, Polyester / PET Carpet, Wool Carpet, Triexta (PTT) Carpet

What you are looking at. A line of tiles rises and meets in a peak, often with a bang, sometimes months or years after installation.

Why it happens. The tile field expanded, had nowhere to go, and the compressive stress released upward. Tile and its substrate move at different rates with temperature and moisture, and that difference has to be absorbed somewhere.

What the standard says. TCNA EJ171 requires movement joints at 20–25 ft maximum indoors, 8–12 ft outdoors, and at every change of plane, transition and perimeter. Perimeter joints must be filled with a compressible sealant. Filling them with grout is a documented cause of tenting, because grout has no give.

Where warranties land. A missing or grout-filled movement joint is an installation defect. The tile did what tile does.

Look at the perimeter before anything else. If grout runs right to the wall under the shoe molding, you have your answer.

Affects: Porcelain Tile, Ceramic Tile, Natural Stone

What you are looking at. Cracks that run through grout joints in a line across several tiles, rather than isolated crumbling in one spot.

Why it happens. The floor beneath is flexing. Grout is rigid and has almost no tensile strength, so it is the first thing to report movement it was never designed to absorb.

What the standard says. TCNA sets deflection limits of L/360 for ceramic and porcelain, and L/720 for natural stone — twice as stiff. An uncoupling membrane is the layer that isolates tile from minor substrate movement, and it is the layer most often deleted to save money.

Where warranties land. Not a grout defect. Grout is the messenger.

A crack that follows one line across many tiles is structural. Crumbling at one joint is usually a mixing or cleaning issue.

How to fix it →

Affects: Porcelain Tile, Ceramic Tile, Natural Stone

What you are looking at. Tap across the floor with a coin or a knuckle and the note changes — some tiles ring solid, others sound like a drum.

Why it happens. The mortar did not make full contact. The trowel ridges were never collapsed, or the mortar skinned over before the tile went down, so the tile is bridging air.

What the standard says. Coverage is verified by pulling a set tile back up and looking at the back — the ridges should be flattened and the back substantially covered. This is a check made during installation, not after.

Where warranties land. An installation defect. A hollow tile is not necessarily loose today, but it is where the floor will crack under a point load.

Some hollow sound near a wall or over an uncoupling membrane is normal. A pattern of it across the field is not.

How to fix it →

Affects: Porcelain Tile, Ceramic Tile, Natural Stone

What you are looking at. Pale, matte patches where something was spilled — often ring-shaped, often in a kitchen or a bathroom.

Why it happens. Acid has dissolved the surface of the stone. Marble, limestone and travertine are calcareous, so lemon, wine, vinegar, tomato and many bathroom cleaners chemically attack them. The mark is missing stone, not a stain sitting on top.

What the standard says. The Natural Stone Institute distinguishes calcareous from siliceous stone precisely because they behave differently here. A sealer slows absorption of stains; it does not stop an acid reaching the surface.

Where warranties land. Excluded as a characteristic of the material. It was disclosed, in the sense that it is what the stone is.

This is why the honest question about marble is not whether it will etch, but whether you will mind.

How to fix it →

Affects: Natural Stone

What you are looking at. Trowel lines, plywood joints, fastener heads or old adhesive patterns visible as raised marks through the finished floor, usually in raking light.

Why it happens. Thin, flexible flooring conforms to whatever it is laid over. It does not bridge irregularity; it copies it, and light does the rest.

What the standard says. Substrate flatness tolerances are typically 3/16" in 10 ft, tightening for large-format tile. Every ridge above that tolerance is still there after the floor goes down.

Where warranties land. A substrate preparation issue. Excluded from product warranties, and the reason preparation is the largest hidden line item in a resilient quote.

Thicker rigid-core products hide more of it. They do not fix it.

Affects: Luxury Vinyl Plank — Flexible (Glue-Down), Sheet Vinyl, VCT — Vinyl Composition Tile, Luxury Vinyl Plank — SPC (Rigid Core), Luxury Vinyl Tile (LVT)

What you are looking at. Joints that were tight at handover slowly open, often at one end of a run or in a room with strong sun.

Why it happens. A floating floor is one large panel that has to move as a unit. If it is pinned — by a heavy island, a transition screwed through it, trim nailed into the plank rather than the wall — one part is held while the rest moves, and it separates at the weakest joint.

What the standard says. Expansion gap at every wall and obstruction, and the manufacturer will state a maximum run before a transition is required. Rigid cores also move with temperature, which is why direct sun through glass matters.

Where warranties land. Depends on which happened. A pinned floor is installation. Exceeding the stated maximum run without a transition is installation. The plank itself rarely is.

Check whether the shoe molding is nailed to the wall or through the floor. It should be the wall.

How to fix it →

Affects: Luxury Vinyl Plank — SPC (Rigid Core), Luxury Vinyl Plank — WPC (Wood-Plastic Core), Laminate, Engineered Hardwood, Luxury Vinyl Tile (LVT)

What you are looking at. Small permanent depressions where a refrigerator, a piano caster or a chair foot has stood.

Why it happens. Foamed cores contain air, and air is what makes them warm and quiet underfoot. It is also what makes them yield under a concentrated point load and not fully recover.

What the standard says. This is the trade-off named in the product description rather than a defect. Denser stone-composite cores resist it and feel harder in exchange.

Where warranties land. Point-load damage is excluded. Wide floor protectors are the stated requirement in most manufacturer care instructions, not a suggestion.

The softer, warmer, quieter floor and the dent-resistant floor are not the same floor.

How to fix it →

Affects: Luxury Vinyl Plank — WPC (Wood-Plastic Core), Sheet Vinyl

What you are looking at. Dull, scuffed, graying traffic lanes on a tile that is barely a year old.

Why it happens. The tile is not the wear surface — the acrylic finish on top of it is. When that finish is not stripped and rebuilt on schedule, you are walking on abraded finish, and eventually on the tile itself.

What the standard says. A typical maintenance program is daily dust and damp mop, burnishing weekly to monthly, and a strip-and-refinish cycle once or twice a year, at roughly $1.00–$2.00 per sq ft per year in labor and materials.

Where warranties land. Nothing to claim. The product performed; the program did not happen.

The cheapest floor in this guide to buy, and one of the most expensive to keep. That is the whole story of VCT.

Affects: VCT — Vinyl Composition Tile

What you are looking at. The coating releases in patches or peels back in sheets, often starting at an edge or a saw cut, sometimes taking a thin skin of concrete with it.

Why it happens. The bond was never made. Either the slab was too smooth for the coating to key into, or it was still giving up moisture, and vapor pressure pushed the coating off from beneath.

What the standard says. ICRI Guideline 310.2R sets concrete surface profiles: CSP 1–2 for thin sealers, 3–5 for high-build systems, 6+ for overlays. Slab moisture is tested to ASTM F2170, which caps at 75% RH unless the manufacturer states otherwise.

Where warranties land. Preparation is excluded from coating warranties, and preparation is the cause in almost every case. A coating cannot be better bonded than the surface it was put on.

If the underside of a lifted piece is smooth and shiny, it never keyed in. If it is damp or chalky, moisture did it.

How to fix it →

Affects: Epoxy & Resinous Coatings

What you are looking at. A shallow network of fine cracks across the surface, most visible when the floor is wet or in low light, with no displacement between the two sides.

Why it happens. The surface dried faster than the body of the slab and shrank against it. It is a surface-depth condition and it was very likely there, invisible, before grinding exposed it.

What the standard says. Polishing does not add a material — it grinds the slab you already own. Existing crazing, color variation, trowel marks and patch repairs are revealed by the process, not created by it.

Where warranties land. Nothing to claim against a product, because there is no product. This is why a test panel on the actual slab matters more here than on any other floor.

Crazing is cosmetic and shallow. A crack you can catch a fingernail in, or that has displacement, is structural and is a different conversation.

How to fix it →

Affects: Polished Concrete

What you are looking at. A single crack crossing the field, often in a straight line, sometimes tracking a joint or a crack you can trace in the slab below.

Why it happens. Terrazzo is poured in one continuous piece bonded to the slab. It has no joints of its own to absorb movement, so when the slab beneath moves or cracks, the topping reports it faithfully.

What the standard says. NTMA practice puts divider strips where movement is expected — over slab joints and at changes of direction — precisely because they decide where the material is allowed to crack. Epoxy terrazzo is nominally 3/8" thick and telegraphs what is underneath.

Where warranties land. Substrate movement is excluded. The strips are the design decision that determines whether a crack lands on a line that looks deliberate.

Terrazzo has no grout joints, which is its great advantage and the reason it has nowhere to hide a crack.

How to fix it →

Affects: Terrazzo

Quick checks

Before you make a claim

Four checks that cost nothing and settle most arguments about cause:

Confirmations beyond that are physical — a moisture meter on the slab, a tile pulled to inspect coverage. Worth doing before anyone agrees who pays.

Common questions

Flooring failures — frequently asked

Not the flooring. Across the twenty failure modes documented on this page, only two are primarily about water reaching the product, and none are really about the product being defective. The recurring causes are moisture arriving from the building, a substrate that was not flat, stiff or dry enough, movement that was given nowhere to go, and installation shortcuts — most often a missing expansion gap, a knee kicker used instead of a power stretcher, or grout where a compressible sealant belonged.

It was almost certainly not power stretched. CRI 104 and CRI 105 make a power stretcher mandatory and call for roughly 1 to 1.5 percent stretch across both the length and the width. A knee kicker is a positioning tool, not a tensioning one, and carpet installed with one alone will relax into waves within months. This is an installation defect rather than a product defect, so the mill warranty will not cover it but the installation warranty generally will. Left alone the crests abrade and the backing can delaminate, which turns a re-stretch into a replacement.

Filtration soiling. Air is moving through the carpet at its edges and the pile is behaving like an air filter, trapping very fine airborne soil — cooking oils, combustion particles, fine clay. The carpet is not dirty in the ordinary sense. CRI attributes it to airflow through carpet and edges, often from an unbalanced HVAC system where more air enters a room than can leave it. Sealing gaps under baseboards and in the subfloor reduces it, as does leaving interior doors open while the system runs. It is excluded from carpet warranties because it is a building condition, and it will return if the airflow does not change.

Pooling, also called watermarking, pile reversal or shading. The pile has permanently reversed direction in those areas, so you are seeing light reflect off the side of the yarn rather than the tip. CRI states that pile reversal is not a manufacturing defect, is not caused by the materials or the manufacturing process, and is difficult if not impossible to predict or prevent. It is most common in dense, smooth, plush cut-pile carpet. There is no accepted correction and it is excluded from essentially every warranty, usually by name.

That is tenting, and it means the tile field expanded with nowhere to go. TCNA method EJ171 requires movement joints at a maximum of 20 to 25 feet indoors, 8 to 12 feet outdoors, and at every change of plane, transition and perimeter. Perimeter joints must be filled with a compressible sealant. Filling them with grout is a documented cause of tenting, because grout has no give at all. The check is simple: lift the shoe molding and see whether grout runs hard to the wall.

Not until it has dried and stopped moving, and that is a measurement rather than a judgment. Cupping means the underside is wetter than the top, so the board has swollen at the bottom and its edges have lifted. Fix the moisture source first — usually a crawl space, a slab or a leak — and the floor will often flatten on its own. Sanding a cupped floor flat while it is still wet removes the raised edges, and when the board finally equalises it becomes crowned instead: high in the middle, with the material that would have made it flat now gone. It is the clearest case in flooring of a repair creating the defect.

Usually not against the manufacturer, which is the uncomfortable part. Product warranties cover the product, and most of what goes wrong with floors is moisture from the building, substrate preparation, or installation. Several of the most upsetting problems — pooling, seasonal gapping, etched marble, dimples under a refrigerator foot — are excluded specifically because the material is behaving exactly as designed. That does not leave you without recourse: installation defects are real, they are usually visible, and they are generally covered by whoever did the work.

Often you can narrow it a long way, which is what this page is for. Cupped boards point beneath the floor. Crowned boards point at a sander used too early. A ridge of tented tile points at the perimeter joint. Waves in carpet point at the stretcher. But the confirmations are physical — a moisture meter on the slab, a tile lifted to check mortar coverage, the shoe molding pulled to see whether an expansion gap exists. Those are worth doing before anyone agrees who pays.

Care and Maintenance by Material → Where These Standards Come From →