Hardwood Refinishing Explained: What Sanding and Recoating Actually Involves, What It Costs ($3 to $8 a Square Foot), When a Floor Can Be Refinished and When It Cannot

What a refinish actually is

1. Clear the room to the walls. Everything out, including the quarter-round if there is any. The crew covers doorways with plastic; the dust still gets everywhere.
2. Three passes with the drum or belt sander. Coarse (36 grit) to take off the finish and flatten the boards, medium (60) to take out the coarse scratches, fine (80 or 100) to leave a surface the stain will take evenly. An edger does the two feet along the walls and a scraper does the corners. This is where a bad crew leaves the “edger marks” you see as a halo around the room in low light.
3. Water-pop and stain, if staining. Wetting the raw wood opens the grain so the stain goes in evenly. Stain the next day; dry a day.
4. Three coats of finish. Oil-modified polyurethane (amber, tough, smells for a week, a day between coats) or waterborne (clear, less smell, two coats a day, harder in the good brands). Each coat gets a light screening before the next.
5. Stay off it. Walk in socks after 24 hours, furniture after 3 or 4 days, rugs after 2 weeks. The finish keeps curing for a month.

The whole job on a typical main floor is five to seven working days, and you are not living in those rooms while it happens. Dustless systems with a vacuum on the sander cut the mess by most of it, not all of it.

What it costs

Stairs are $40 to $75 a tread on top of the floor rate. Small jobs carry a minimum because the sanders have to come either way; expect $900 to $1,200 for one room. The master price table has new flooring to compare against.

When it is possible

Solid 3/4 in. hardwood: nearly always. There is about 1/4 in. of wood above the tongue and each sanding takes 1/32, so a floor has five or six in it. The checks are whether the boards are still tight to the subfloor (loose boards get screwed from below or face-nailed first), whether the floor has been sanded so many times the nail heads are showing at the edges, and whether there is 1/8 in. of cup across the boards, which the sander will flatten but will take most of a sanding to do.

Engineered hardwood: it depends entirely on the wear layer. A 2 mm veneer takes a screen and recoat and nothing more; a drum sander goes through it to the plywood in one pass along the edge. 3 mm takes one careful sanding by someone who knows it is engineered. 4 mm and up refinishes like solid, once or twice. If you do not know the wear layer, pull the register in the hallway and look at the edge of a board. The wear layer page has the full table.

The floor is finished, in the other sense, when: water has gotten under it and the boards are black and soft; pet urine has gone through to the subfloor over a wide area (the stain can be sanded, the smell cannot); the boards have been sanded to the tongue; or it is a 1980s parquet of 5/16 in. slats with nothing left to sand. Then it is a new floor, and the removal is $2.00 a square foot before the new one goes down.

Refinish or replace: 800 sq ft of 1970s red oak strip

A main floor under carpet, found in good shape, two water stains at the patio door, one closet with a cut-out from an old vent.

The refinish is 41% of the replacement and you keep a 3/4 in. solid floor with four sandings left in it. The replacement gets you a 7-in. plank and a colour you chose; that is a real reason, but it is not a money reason. Solid hardwood costs if you want to compare against new solid instead.

Where homeowners go wrong

1. Hiring the lowest bid on a floor that has been sanded twice already. A crew that leans on the drum takes 1/16 in. where 1/32 would do, and that was the last sanding. Ask how deep they expect to go.
2. Sanding engineered without checking the wear layer. One pass through a 2 mm veneer and the only fix is a new floor.
3. Choosing a grey stain on red oak and expecting the sample board. Red oak is pink under grey. White oak takes it; red oak needs a bleach or a different plan, and a good finisher will tell you so before, not after.
4. Moving the furniture back in on day two. Waterborne finish is dry to walk on in hours and hard in weeks. A sofa leg dragged across it on day three is a scar in the new finish.
5. Refinishing a cupped floor before fixing the moisture. The sander flattens it; the cause (a damp crawlspace, a basement with no dehumidifier) cups it again. Cupping and gaps first.

Questions people ask

Sources and further reading

• National Wood Flooring Association: the installation guidelines every hardwood warranty points to: subfloor flatness, moisture limits, acclimation, fastening schedules and the radiant-heat chapter.
• Mirage Hardwood Floors: Quebec-made solid and engineered hardwood; their installation guides give the moisture, acclimation and radiant limits in plain numbers.