You can usually identify a hardwood floor finish in under an hour with a few drops of water, a white rag, four solvents and a little boiled linseed oil from the hardware store. Wax leaves a yellow smear on a rag dampened with mineral spirits. Shellac turns gummy under denatured alcohol. Penetrating oil lets a drop of oil soak in. Polyurethane shrugs off almost everything you put on it.
It’s worth knowing before anyone cleans, recoats or sands the floor. The cleaner that’s right for polyurethane will haze a waxed floor, and a fresh coat of polyurethane won’t stick to wax at all. In Durham this comes up a lot, because a lot of the original floors in our 1940s bungalows and mill houses still have a wax or penetrating oil finish, and plenty of them have something newer on top.
What was put on old floors, and when
Most floors installed or refinished in the last few decades have a polyurethane finish. Before polyurethane took over, floors were usually finished with shellac or varnish, often with paste wax on top that got renewed every so often, or with a penetrating oil that soaked into the wood and left no film on the surface.
So in a house from the 1920s through the 1950s, the kind you find in Trinity Park, Watts-Hillandale, Forest Hills and Old North Durham, any of the four could be on the floor. It could also be two of them stacked up, because a previous owner may have waxed over shellac, or put polyurethane over an old finish during a quick refinish decades ago.
Before you open any solvents
Pick a test spot nobody will see. A closet is the usual choice, but closet floors sometimes never got the wax or the cleaning products the rest of the room did. Run your tests in the closet and also in a spot in the main room that a couch or dresser normally covers.
Wear rubber gloves and open the windows. Mineral spirits, denatured alcohol, lacquer thinner and acetone are all flammable, so put out any open flame first, including a gas stove or a pilot light nearby. Use a cotton swab or the corner of a rag and only a few drops at a time.
If you use boiled linseed oil for the oil test, the rag is the dangerous part. Linseed oil rags can heat up on their own as they dry and start a fire. Spread the rag flat outside to dry, or drop it in a metal can of water. Never leave it balled up in the trash.
Start by looking and feeling
Before using any solvent, get down close to the floor in daylight.
A film finish like polyurethane, varnish or shellac sits on top of the wood like a clear skin. When it wears, you see white scratches in the skin, worn patches with an edge around them, and sometimes flaking. An oil finish looks like the wood itself, with a low sheen and no layer you can see. Wear on an oil or wax floor shows up as dry, gray wood without any peeling. Wax tends to look uneven, shiny in some places and smeary in others, especially near walls where it builds up.
Color is a clue too. A deep orange or amber tone on old oak or pine usually comes from shellac, old varnish or oil-based polyurethane, which all darken with age.
The tests, gentlest first
Go in this order. Wax comes first because a layer of wax on top of another finish reacts first in every later test and hides what’s underneath.
1. Water
Put a few drops of water on the floor and leave them for a few minutes. If the spot turns white or cloudy, there’s probably wax on the floor. Shellac can also cloud under water. If the water soaks in and darkens the wood, nothing is protecting the wood in that spot, either because the finish has worn through or because an oil finish needs renewing.
2. Mineral spirits
Dampen a white rag with mineral spirits and wipe once over your test spot. A yellow or light brown smear on the rag means wax. A clean rag means there’s no wax on top, and you can move on.
3. Boiled linseed oil
Put a few drops of boiled linseed oil on the floor. If it soaks into the wood, you have a penetrating oil finish. If it beads up on the surface, the floor has a hard film finish such as shellac, varnish, lacquer or polyurethane, and the next tests will tell you which. Wipe up the oil and deal with the rag as above.
4. Denatured alcohol
Dab on a little denatured alcohol. If the finish gets soft and gummy within a minute or so, it’s shellac.
5. Lacquer thinner
If alcohol did nothing, try lacquer thinner. Lacquer thinner dissolves shellac too, which is why alcohol goes first. If the finish softens now, it’s an older varnish or a lacquer.
6. Acetone
Acetone will also dissolve varnish, in about 30 seconds. If acetone only softens the finish a little without dissolving it, the finish is probably polyurethane.
Fine Homebuilding’s guide to identifying wood finishes runs the same solvents in a similar order, and it’s a useful second reference if you want to double-check a result.
| Test | Result | What it points to |
|---|---|---|
| Water, left a few minutes | Turns white or cloudy | Wax, sometimes shellac |
| Mineral spirits on a white rag | Yellow or light brown smear | Wax |
| Boiled linseed oil | Soaks in | Penetrating oil |
| Boiled linseed oil | Beads up | A film finish; keep testing |
| Denatured alcohol | Gummy within a minute or so | Shellac |
| Lacquer thinner | Softens after alcohol didn’t | Varnish or lacquer |
| Acetone | Softens slightly, doesn’t dissolve | Polyurethane |
When the results don’t add up
Old floors don’t always give a clean answer. Finishes get layered, and decades of cleaning products leave a film that reacts to solvents in odd ways. You may see every solvent soften the surface a little, or get one result in the closet and another in the living room. A mixed result usually means there’s more than one layer, or that the floor is contaminated with polish or oil soap. That’s when it’s worth having someone who works on old floors take a look before you buy any products.
What each finish means for your floor
Wax
A waxed floor shouldn’t be wet mopped. Water spots it, and regular hardwood cleaners can haze it. Dust mop it and renew it with paste wax and buffing. Light scratches often buff right out with matching wax.
Wax is also the one finish you can’t put polyurethane over. The new coat won’t bond, so switching to a modern finish means sanding the wax off completely. Wax loads up sandpaper fast, so expect that job to take more paper and more time than a typical refinish.
Shellac
Shellac is easy to spot repair, because new shellac bonds to old shellac after a light scuffing. It’s also the most delicate of the four. Water leaves white marks on it, and spilled alcohol softens it, which is how a spilled glass of wine can leave a dull ring. Getting a tougher modern finish usually means sanding the shellac off.
Penetrating oil
An oil finish is inside the wood, so scratches go into the wood too, and they often disappear with a little matching floor oil rubbed in. You maintain it with more of the same oil. Moving to polyurethane usually means sanding first, so the new finish has clean bare wood to grip.
Polyurethane and other modern film finishes
Polyurethane is the most common finish on floors today. Oil-based polyurethane ambers over time, and water-based stays closer to the color of the bare wood. Either one cleans up with a pH-neutral hardwood cleaner on a barely damp pad. A worn polyurethane floor can often get a fresh coat without sanding, as long as it’s clean and the new coat will bond.
Prefinished floors from the factory have a very hard coating that resists most of these tests. They’re a different case from site-finished floors, and our post on site-finished vs. prefinished floors explains why.
Lead paint and heart pine in older Durham houses
If your house was built before 1978 and the floor has ever been painted, or has painted borders or trim in the area that would be sanded, lead is a real possibility. Don’t sand a test patch in that case. Our post on dustless sanding covers the EPA’s lead rules and what to ask a refinisher.
Also, look at the wood as well as the finish. A lot of the oldest houses in Trinity Park and Old North Durham have heart pine in place of oak, and it takes stain and sandpaper differently. Our guide to restoring heart pine floors covers how to tell, and the 1940s bungalow post covers what tends to be under those floors.
Frequently asked questions
Can I put polyurethane over a waxed floor?
No. Polyurethane won’t bond to wax, and it will peel. The wax has to be removed, which on most floors means a full sand down to bare wood.
How do I know if my floor has been waxed?
Wipe a hidden spot with a white rag dampened with mineral spirits. A yellow or light brown smear means wax. Water drops that turn white after a few minutes point the same way.
How can I tell shellac from varnish?
Use denatured alcohol. Shellac gets gummy within a minute or so. Varnish doesn’t react to alcohol but softens under lacquer thinner.
Why does my old floor look orange?
Usually it’s an oil-based finish, shellac or old varnish that has darkened with age. Sanding takes it back to fresh wood, and a water-based finish keeps the new color lighter.
Will the solvents damage my floor?
They can mark the finish in the spot you test, which is why you test somewhere hidden and use only a few drops. Acetone and lacquer thinner are the most likely to leave a mark.
How should I clean a floor if I don’t know the finish?
Stick to a dry microfiber dust mop until you know. Water and regular cleaners are fine on polyurethane but can spot or haze wax and shellac. Our guide to cleaning hardwood without wrecking the finish covers routine care, and getting scratches out of hardwood explains which repairs suit which finish.
Want us to tell you what’s on your floor?
We work on old floors all over Durham, from Trinity Park, Watts-Hillandale and Old North Durham to Forest Hills and Hope Valley, and in Chapel Hill, Carrboro, Raleigh, Cary and Wake Forest too. On a free estimate we’ll check the finish and the wood, tell you whether the floor needs cleaning, a fresh coat or a full sand, and email you a written quote, usually within a day or two. Read about our hardwood floor refinishing in Durham, see our Durham refinishing cost guide, or book a free estimate.
Vilchis Hardwood Floors 237 Obie Dr, Durham, NC 27713 (919) 794-1116 · [email protected] Monday to Friday, 9 a.m. to 5 p.m.
Written by Mario Vilchis, owner of Vilchis Hardwood Floors, a family-owned flooring company in Durham, NC that has been installing and refinishing floors across the Triangle since 2009. Mario comes out to every estimate personally.
