Hardwood is the most repairable floor there is, which is the whole argument for it: almost any damage short of rot can be sanded out, filled, or cut out one board at a time, and the floor goes on for another few decades. The trick is matching the repair to the damage. A scratch in the finish and a scratch in the wood are different jobs, and a cupped board is not a sanding problem until the moisture that cupped it is gone.
Look at the mark in raking light. If it is in the clear finish — a lighter scratch on a darker floor, no change in the wood grain — it is a touch-up or a recoat and you can do it. If it goes into the wood — a gouge, a dent, a stain in the grain — it is filled and spot-sanded, or the board comes out. If the boards themselves have moved — cupped, crowned, gapped, buckled — the floor is telling you about moisture, and no repair holds until the moisture is handled and the wood has had a season to settle.
Engineered wood follows the same rules with one limit: the veneer. A 2 mm veneer can be screened and recoated but not sanded more than once, if that; a 4 mm sawn veneer takes two or three refinishes. Below about 2 mm, a damaged engineered board is replaced rather than sanded.
DIY a realistic job for a careful person · Hire it the tools or the skill are the job · Replace a repair costs more than it is worth
Grit under shoes, pet claws, a dragged chair. The scratch is in the polyurethane or aluminum-oxide finish, not the wood.
A scratch that shows bare wood — grayer, rougher, drinks water — is past the finish. That is a spot repair with filler and a spot finish, or a sanding of the area.
A dropped pan, a moved appliance, a heel. The wood itself is dented or torn.
A gouge longer than a few inches, a split board, or a cluster of damage across several boards is a board replacement — cheaper and invisible, where a large filled patch never is.
Moisture from below — a wet crawlspace, a slab, a leak — swells the underside so the edges rise (cupping). Crowning is the reverse, and often a floor that was sanded flat while still cupped and then dried. The diagnosis, on Why Floors Fail →
Boards that have cupped hard enough to split, lift nails or buckle are replaced, and the subfloor under them checked for rot.
Wood shrinks in dry winter air and swells in summer. Gaps that open every winter and close every summer are normal and should be left alone; gaps that stay open year-round are from a floor installed too wet or a house kept too dry. The diagnosis, on Why Floors Fail →
Gaps across a whole floor that opened after a wet installation, with boards that have also cupped or split, are a refinish at best and a replacement if the boards have moved past the point of closing.
Water — a plant pot, a pet, a leak — that sat long enough to react with the tannins in the wood. The dark stain is in the grain, often deeper than a sanding reaches.
Pet urine that has been sitting for months, or a stain that has spread across several boards, is a board replacement; no bleach reaches it and a sanding deep enough to would go through the wear layer.
Any damage that a filler cannot hide: a split, a burn, a deep stain, a rotted board under an old leak.
When several boards in the same area need replacing and the floor is site-finished, the room is usually refinished anyway; if the veneer on an engineered floor is too thin to sand, the replacement is the only option, and it is only as good as the match.
The finish has worn through in the traffic lanes, the floor has been repaired in too many places, or the scratches are everywhere.
A solid floor sanded so many times that the tongue is exposed, or an engineered floor whose veneer is through, cannot be sanded again. That floor is replaced, and it usually took fifty years to get there.
Yes, if the scratches are in the finish rather than the wood. A color-matched marker or wax stick hides a few; a screen and recoat — a light abrasion of the finish and one fresh coat — fixes a floor that is scratched and dull across the traffic lanes, in a day, with no sanding. A scratch that shows bare wood needs a spot repair or a sanding.
A touch-up is the price of a marker. A screen and recoat runs about $1 to $2 per square foot. A single board replacement is $150 to $400 with finishing. A full sand and refinish is $3 to $5 per square foot, and it is the point past which most people compare it to the cost of a new floor.
Usually, and usually by waiting. Cupping is a moisture imbalance; find and fix the source, let the boards dry over weeks to a season, and most of the cupping goes with the moisture. Whatever remains is sanded flat once a meter shows the boards stable. Sanding a floor that is still wet locks the cupping in and produces crowning later.
First decide which gap it is. Seasonal gaps open in winter and close in summer and should be left alone; filling them means the filler is crushed out in July. Permanent gaps are filled with a flexible color-matched filler before a recoat, or with glued slivers or rope in wide-plank floors. A humidifier in winter prevents the next set.
Yes. The damaged board is cut lengthwise with a circular saw set to its thickness, chiseled out, and a matching board with its bottom groove lip removed is glued and nailed into the space. On a prefinished floor with attic stock the repair is invisible; on a site-finished floor the area is sanded and blended or the room refinished.
Almost always, if the floor is solid or an engineered floor with veneer left. A refinish costs a fraction of a new floor, and the NAR’s remodeling survey rates refinishing existing hardwood as the highest-return interior project there is at resale. The one time it is not worth it is a floor sanded down to the tongue, which has no sandings left.