The short version
- Only the wood above the tongue can be sanded, roughly a quarter inch on a traditional solid floor, and that is the whole budget for every refinish the floor will ever get.
- Scratches, gray traffic lanes, dull finish and a color you dislike are refinishing problems. Rot, a spent wear layer and a failed subfloor are replacement problems.
- There is a third answer that is often the right one: replace the damaged boards, weave them in, and refinish the room as one surface.
- In our data at /data/, 138 of 635 places have 35 percent or more of their housing built before 1940, which is the stock where the wear layer has to be measured before anyone quotes.
- When two quotes disagree, ask each contractor how the remaining wood was measured. A guess from standing height is not a measurement.
The measurement that decides it
A solid floor can be refinished while there is wood left above the tongue, and it cannot once that wood is gone, whatever the surface looks like.
A solid hardwood board is about three quarters of an inch thick when it is new, with a tongue milled along one edge and a groove along the other. The fasteners go through the tongue. Everything above that line is wear layer, roughly a quarter inch on a traditional strip floor, and every sanding the floor ever receives comes out of it.
That quarter inch normally buys four or five full sandings across the life of the floor. The difficulty is that nobody leaves a record. A house built in 1925 has had several owners, and the floor may have been sanded once or four times. The surface looks the same either way.
So the measurement is taken at the edge of a board, where the profile is exposed: under a floor register, at a threshold, or where a board meets a stair opening. If there is wood above the tongue, refinishing is on the table. If the tongue is starting to show between boards, or nail heads are appearing in the field of the floor, the wear layer is spent.
A floor can look tired and have four sandings left in it, or look fine and have none. The surface does not tell you which.
What refinishing fixes, and what it does not
Refinishing fixes everything that lives in the finish and in the top of the wood, and nothing that comes from underneath the floor.
Sanding removes the old coating and a thin layer of wood with it. That takes out scratches, the gray paths where the finish wore through, most surface staining, sun fade and the color itself. A floor that is orange and dated can come back natural, darker or lighter, because the color is decided again from bare wood.
What sanding does not reach is anything deep or structural. Dark pet stains and old plant pot rings usually go further into the board than a sander can follow. Boards that move, squeak or flex are responding to the subfloor or the framing. Cupping caused by moisture under the floor comes back if the moisture is still there.
None of those rule refinishing out. They mean something else has to happen first: stained boards replaced, loose boards fastened, the moisture source found. A quote that skips that step and prices sanding alone is the one that looks cheapest and ends up costing more.
When replacement is the honest answer
A floor has to be replaced when the wear layer is spent, when the boards have rotted, or when the structure under them has failed over a large part of the room.
A spent wear layer is the clearest case. Once the tongue is exposed along the board edges, another sanding cuts into the part of the board that holds the floor together. Boards split along the groove and start to lift. There is no finish that solves that.
Water is the second case. A floor that stayed wet long enough for boards to rot, or for the subfloor underneath to go soft or delaminate, needs to be opened up. Putting a new finish on top of a failing subfloor produces a good looking floor that moves.
The third case is engineered flooring with a thin wood layer. Some products carry four millimeters of real wood and can be sanded. Others carry less than two and cannot. When a thin engineered floor is worn through, replacement is the only real option, and it is better to hear that at the estimate than halfway through the job.
Replacement is sometimes sold because it is the bigger job, and refinishing is sometimes sold because it is the easier one to schedule. Ask what was measured.
The answer in between: replace boards, then refinish the room
When the damage is limited to part of the floor, the right job is usually to replace those boards, weave the new ones into the old, and sand and finish the whole room together.
This is the option people are least often offered, and in older housing it is the one that fits most often. A stained area by a back door, a section ruined by a radiator leak, the boards where a wall was removed: each of these is a repair inside a floor that is otherwise sound.
The new boards are laced in on a stagger, so there is no straight line where the repair starts and ends, and they are matched to the width and species of the original. Then the room is sanded and finished as one surface. That last step is what makes the repair disappear, because new finish next to old finish always shows as a patch.
Matching matters more in older floors. Narrow strip oak from the early twentieth century was cut from denser timber and milled to widths that are not standard today. Sometimes the right replacement is reclaimed flooring of the same age. In postwar houses the common two and a quarter inch red oak is still a standard board, and the match is straightforward.
| What you see | Usual answer | Why |
|---|---|---|
| Dull finish, light scratches, wood not exposed | Screen and recoat | The damage is in the coating, so no wood needs to come off. |
| Gray traffic lanes, scratches you can feel | Full refinish | Wear has reached the wood, and only sanding gets below it. |
| Dark stains or damage in one area | Replace boards, then refinish the room | Deep stains outlast sanding, and the room is finished as one surface. |
| Tongue showing, nails appearing, boards splitting | Replace the floor | The wear layer is spent and the boards no longer hold. |
| Soft, spongy or sagging areas | Open the floor up first | The problem is the subfloor or the framing, and the wood on top is not the fix. |
What the age of your house tells you before anyone visits
The year the house was built predicts what kind of floor is there and how much of it is likely to be left, and in this region the houses are old.
We publish the housing data for 635 towns and Philadelphia neighborhoods at /data/, built from the American Community Survey. Across that area approximately 60.5 percent of 3,899,409 housing units were built before 1978. In Philadelphia the figure is approximately 82.8 percent, and 40.0 percent of the city predates 1940.
Those numbers translate into floors. In the 138 places where 35 percent or more of the housing predates 1940, the typical floor is original narrow strip oak, often nailed straight to the joists, and it has usually been sanded before. That is where measuring first matters most, and where the answer is most often the in between one.
At the other end, 216 of the 635 places have a median home built in 1980 or later. Floors there are more often prefinished or engineered, and the question changes from how much has been sanded away to how thick the wood layer was to begin with.
What each choice does to the house while the work is on
Refinishing takes the rooms out of use while the finish cures, and replacement adds demolition, trim work and usually a change in floor height.
Refinishing means furniture out, the work area sealed, sanding in passes and finish in coats. The floor can be walked on in socks well before it has cured, and those are two different milestones. Rugs and heavy furniture go back on the cure schedule of the finish that was used, which we give you in writing before the job starts.
Replacement starts with taking the old floor up. Baseboards and shoe molding often come off, door casings may need to be undercut, and the new floor may finish at a different height from the one beside it, which affects thresholds, stair landings and appliances.
In a house built before 1978 both jobs can fall under the federal lead rule, because both disturb painted trim. That is a reason to ask how the dust will be contained, and it is not a reason to choose one job over the other.
How to read two quotes that disagree
When one contractor says refinish and another says replace, the useful question is what each of them measured, and where.
A recommendation to replace should come with a reason you can see: the tongue visible at a board edge, a moisture reading, a soft area you can press with your foot. A recommendation to refinish should come with the same kind of evidence, which is the remaining thickness measured at an exposed edge.
Be cautious with a quote given from the doorway. It may still be right, and it was not checked. Be equally cautious with a quote that prices a full replacement for damage in one corner of one room.
We look at every floor in person before quoting, and the visit is free. If the floor only needs a recoat we say so, since that is the smallest job we do and often the correct one.
