Refinishing a floor in a house that is older than the advice you are reading

How much floor is actually left

Only the wood above the tongue can be removed, which is roughly a quarter inch on a traditional solid floor, and that quarter inch is the entire budget for every sanding the floor will ever get.

A solid board is milled with a tongue on one edge and a groove on the other, and the fastener goes through the tongue. Everything above that line is wear layer. Everything below it is structure, and cutting into it means the floor stops holding.

That budget buys four or five sandings across the life of the floor. In a house built in 1925 that has changed hands four times, some of those sandings have already been spent, and nobody left a record. So the measurement happens at the edge of a board, usually at a doorway or a heat register where the edge is exposed, before anyone quotes a full sanding.

This is the single most common place where a cheap quote turns expensive. A crew that does not measure and sands anyway can take a floor that had one refinish left and end it.

Why the age of the housing changes the work

Pre-1940 stock is usually narrow strip oak nailed straight to the joists with no plywood in between, and pre-1978 stock brings a federal rule that governs how the sander is allowed to be built.

The data we publish at /data/ puts numbers on this rather than leaving it as a feeling. Across the 635 towns and Philadelphia neighborhoods in our dataset, 60.5 percent of 3,899,409 housing units predate 1978. Philadelphia itself is 82.8 percent, and 45 of its 132 residential neighborhoods are above 90 percent.

In practice that means two things. The first is construction: older floors are frequently narrow strip oak, sometimes heart pine on upper floors, laid directly over joists. There is no subfloor to absorb error, and squeaks are structural rather than cosmetic.

The second is regulatory. Paid work that disturbs painted surfaces in pre-1978 housing falls under 40 CFR Part 745, and floor sanding reaches painted surfaces more often than people expect, because the edger runs to the baseboard and the shoe molding. That rule specifies containment and vacuum equipment at the point of generation. It is a description of how a machine has to be assembled, not a suggestion about cleanliness.

Dustless, and what the word actually covers

Vacuum extraction catches most of the dust and never all of it, and any crew promising zero is selling a word rather than describing a process.

A modern sanding setup connects the machine to a vacuum that collects at the point where the dust is made. It changes the job substantially. It does not make the job dust free, and the fine airborne fraction is the part no shroud captures completely.

We say this in writing because the alternative is an argument on day two. What you should expect is containment at the doorways, a machine with extraction attached, and a house that needs cleaning afterwards anyway, just far less of it.

In pre-1978 housing the same equipment is doing double duty, because it is also what the federal rule requires. That is a good thing to understand as a homeowner: the dust control is not a premium upgrade in an old house, it is the baseline the law describes.

The option most people are not offered

When the finish is worn but the wood underneath is not, a screen and recoat renews the surface without removing any wood, and it costs a fraction of a full sanding.

Screening abrades the existing finish just enough for a new coat to bond, and then a new coat goes down. No wood comes off, so the sanding budget is untouched and the floor keeps every refinish it had left.

It works when the damage is in the finish: dullness, light scratching, traffic paths. It does not work when the damage is in the wood, which is why deep gouges, pet stains and cupping are outside its range.

The reason it is under-offered is straightforward: it is a smaller job. We would rather do the small one when the small one is correct, because a floor that gets recoated every several years is a floor that may never need a full sanding again.

What gets repaired before the sander arrives

Loose boards are fastened, protruding nails are set, and stained or split boards are replaced before sanding, because a sander amplifies every one of those problems.

An old floor nailed straight to the joists has had a century to work loose. Boards that shift underfoot get refastened first. A sander riding over a moving board cuts it unevenly, and the finish later cracks along the same seam.

Old floors are also full of metal. Face nails from earlier repairs, carpet tacks and staples all have to be pulled or set below the surface. A nail head that meets a sanding drum tears the abrasive and leaves a gouge across the next several feet.

Then come the boards that will not sand clean: dark stains around a radiator valve, the ring where a plant sat for years, a board split along its tongue. Those are cut out and replaced with wood matched for width and species, woven in on a stagger so the repair does not read as a patch.

Old finishes change what is possible

Floors from before the 1960s were often finished with shellac or varnish and maintained with wax, and wax in particular decides whether a simple recoat will hold.

Polyurethane became the standard floor finish in the second half of the twentieth century. Before that, floors were shellacked or varnished and kept up with paste wax. Many of those floors have since been sanded and recoated. Some have not, especially under carpet that went down decades ago.

For a full sanding this matters little, since everything comes off down to bare wood. For a screen and recoat it matters a great deal. A new coat of finish does not bond over wax, and a floor recoated without checking can peel in sheets within months.

So on an older floor we test adhesion in a small, out of the way area before recommending a recoat. If the test fails, the choice is a full sanding or leaving the floor as it is, and we say so before any money is spent.

Choosing the finish for old oak and pine

Oil modified polyurethane adds an amber tone that deepens with age, waterborne finishes stay close to the color of the bare wood, and on an old floor the choice is mostly about which color you want to live with.

Most original floors in this housing are red oak, with heart pine on some upper floors. On red oak an oil modified finish gives the warm honey color many people associate with an old house. A waterborne finish leaves it paler and a little pink, which suits a lighter, more contemporary room.

Heart pine is already strongly colored and darkens on its own with light. Under an oil modified finish it goes deep orange red. Under waterborne it stays closer to what you see when it is freshly sanded.

Both types are walkable long before they are cured, and the cure time is different for each. We name the product in the quote and give the schedule for it, so the decision is made on color and on how soon the rooms are needed, with both facts on the table.

Living in a rowhouse while the floor is done

In a narrow house with one stair and one hall, the work has to be sequenced so the family can still reach the bedrooms and the bathroom.

A typical Philadelphia rowhouse has its hardwood on the first floor and in a hall and bedrooms above, connected by a single staircase. Refinishing all of it at once closes the whole house. Doing it in two phases, one floor at a time, usually lets a family stay.

The first floor is the harder phase, since the front door, the stair and the kitchen are all on it. The common arrangement is to coat at the end of the day and use the back door or stay upstairs overnight. Some families simply plan a few nights away for that phase.

Furniture is the other constraint in a small house. There is rarely a spare room to hold it. We ask at the estimate where it will go, since a floor cannot be sanded around a dining table.

How to read an estimate for an old floor

A sound estimate states how the remaining wood was measured, lists the repairs, names the finish and says how dust will be contained.

The measurement comes first. The estimate should say that the floor was checked at an exposed board edge and that there is wood to sand. Without that line, nobody knows whether the job is possible.

Repairs should be listed with a count or an area: boards to replace, sections to refasten. The finish should be named by product and number of coats. In a house built before 1978, the estimate should describe containment and vacuum extraction, since the federal rule requires them where painted trim is disturbed.

Then there is the schedule, with the dates for walking on the floor, moving furniture back and laying rugs. An estimate with all of that in writing is one you can compare with another. A single figure and a start date is not.