Solvents don't get as much attention as stains and finishes, but they're an important part of the finishing process.
Sooner or later, you'll need a solvent to thin a finish, clean a brush, adjust drying characteristics, or clean up after a finishing job. That's when knowing the difference between mineral spirits, alcohol, lacquer thinner, naphtha, and other solvents becomes important.
The key is matching the solvent to both the finish and the task. Solvents aren't interchangeable, and using the wrong one can create application problems or even damage an existing finish.
What Does a Finishing Solvent Do?
The word solvent is often used broadly, but solvents can perform a couple of different jobs. A true solvent dissolves the resins or other solids in a finish, allowing the material to remain liquid and be applied to the wood.
A thinner reduces the viscosity of a finish, making it easier to brush, wipe, or spray. The distinction can get blurry because the same liquid may perform both jobs depending on the finish.
For practical purposes in the shop, the important question is simpler: Which solvent is compatible with the finish you're using and the job you're trying to accomplish?
Quick Guide to Common Wood Finishing Solvents
I'd add this table near the top. It gives the page a useful at-a-glance answer before getting into the details.
Note: Formulations vary. Always check the finish and solvent labels for compatibility before mixing products.
Turpentine
Turpentine is one of the traditional solvents of woodworking and finishing. It's distilled from the gum or sap of certain pine trees, which accounts for its distinctive pine-like odor.
It was once commonly used with linseed-oil-based paints, varnishes, and other oil finishes.
Today, mineral spirits have largely replaced turpentine for everyday thinning and cleanup.
One reason is turpentine's relatively slow evaporation rate. When added to an already slow-drying oil or varnish finish, it can extend the drying time.
Turpentine still has a place in some traditional finishing mixtures, including certain beeswax-and-turpentine finishes.
Mineral Spirits
For most woodworkers, mineral spirits are one of the most useful finishing solvents to keep on hand.
Mineral spirits are petroleum distillates commonly used with:
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Oil-based varnishes
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Oil-based stains
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Oil/varnish finishes
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Oil-based paints
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Brush and tool cleanup
They're also commonly used when a compatible oil-based finish needs to be thinned for easier application.
Standard vs. Low-Odor Mineral Spirits
Not every container of mineral spirits contains exactly the same formulation.
You'll commonly see products labeled standard, low-odor, or odorless mineral spirits. The refining process and composition vary, which can affect odor, evaporation, and solvent characteristics.
Low-odor products can make working with mineral spirits more pleasant, but low odor doesn't mean harmless. Use the ventilation and protective equipment specified by the product manufacturer.
Woodsmith Tip: When you're using mineral spirits to thin a finish rather than simply clean tools, check the finish manufacturer's directions first. Compatibility matters more than what's printed in large type on the front of the solvent container.
Mineral Spirits vs. Paint Thinner
Here's a common source of confusion: Are mineral spirits and paint thinner the same thing? Sometimes.
A product labeled paint thinner may consist primarily or entirely of mineral spirits. Other paint thinners can be blends of different solvents.
Read the label rather than assuming the two products are identical.
When you're thinning a woodworking finish, use the type of thinner specifically recommended by the finish manufacturer. A generic paint thinner may be perfectly suitable for some jobs, but knowing what's in the container removes the guesswork.
Naphtha
Naphtha is another petroleum-derived solvent, but it has one characteristic that makes it particularly useful: it evaporates quickly.
That faster evaporation can be helpful when you don't want a solvent hanging around on the surface for an extended period.
Naphtha can be useful for certain finishing operations, including thinning compatible products where faster evaporation is desirable and cleaning during some finishing processes.
It's also been used with products such as paste wood filler and oil-based stain when a faster-evaporating solvent is appropriate.
As always, check the product directions before substituting one solvent for another.
Alcohol and Shellac
If you use shellac, alcohol is an important finishing solvent.
Alcohol dissolves shellac resin and can also be used to thin compatible shellac for application. Its high volatility is one reason shellac dries so quickly.
One important update here is terminology.
Rather than telling readers that denatured alcohol is simply ethanol with methanol added, I'd keep the modern copy broader. Products sold as denatured alcohol can have different formulations depending on the manufacturer and location.
For shellac, choose an alcohol product that's suitable for the shellac you're using and follow the shellac manufacturer's recommendations.
Alcohol is also used with certain alcohol-soluble dyes.
Lacquer Thinner
Lacquer thinner combines high volatility with strong solvent action.
Its primary woodworking use is thinning compatible lacquer products, but its solvent strength also makes it useful for certain cleanup jobs.
Unlike a single chemical such as acetone, lacquer thinner is generally a blend of solvents. The exact formulation can vary depending on the product and its intended use.
That matters because different lacquer thinners may behave differently.
Some formulations are designed for particular lacquer systems or application conditions. So when you're thinning lacquer, use a thinner that's compatible with the lacquer rather than assuming every can labeled lacquer thinner will perform identically.
Lacquer thinner can also soften or damage many cured finishes. Keep that in mind whenever you're using it for cleanup around a finished project.
Acetone and Other Strong Solvents
You'll also encounter solvents such as acetone and other specialty solvents in finishing products.
These generally fall toward the strong, highly volatile end of the spectrum.
They may be used as components in solvent blends, as thinners for specific coatings, or for particular cleaning operations.
For most everyday woodworking finishes, you don't need a shelf full of specialized solvents. Buy these products when a specific finish or process calls for them rather than trying to use them as universal thinners or cleaners.
Which Wood Finishing Solvent Should You Use?
The simplest approach is to start with the finish rather than the solvent.
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If you're using an oil-based varnish or stain, mineral spirits may be appropriate.
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If you're working with shellac, you'll need a compatible alcohol.
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If you're applying lacquer, use the lacquer thinner recommended for that finish.
For other finishes, check the label before adding anything.
Woodsmith Tip: Don't Guess. A solvent that works perfectly with one finish can cause problems with another. Before thinning a finish, check the manufacturer's instructions for both the recommended solvent and the amount that can be added.
Solvent Safety in the Woodshop
Finishing solvents deserve the same care as the power tools in your shop.
Many solvents produce flammable vapors, and some can be harmful through inhalation, skin contact, or other exposure.
A few basic precautions should always be part of your finishing routine:
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Read the product label and Safety Data Sheet.
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Provide the ventilation specified for the product.
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Use appropriate gloves, eye protection, and respiratory protection when required.
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Keep solvents away from flames, pilot lights, sparks, heaters, and other ignition sources.
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Keep containers closed when you're not using them.
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Store solvents according to the manufacturer's directions.
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Dispose of solvents and finishing waste according to local requirements.
Don't use smell as your safety gauge. A product marketed as low-odor or odorless can still contain solvents that require careful handling.
Keep the Right Solvents in Your Finishing Supplies
You don't need every solvent on the hardware-store shelf.
For most woodworkers, the better approach is to keep the solvents required by the finishes you use regularly and purchase specialty solvents when a particular project calls for them.
More importantly, keep the solvent with the finish it belongs to. Knowing that mineral spirits goes with one finish, alcohol with another, and lacquer thinner with another removes much of the confusion surrounding finishing solvents.
Once you understand those relationships, choosing a solvent becomes much less about chemistry and more about simply matching the right product to the job.
RELATED ARTICLE: 12 Essential Wood Finishing Supplies for Your Workshop
Not Sure Which Wood Finish to Use?
Choosing the right solvent starts with choosing the right finish. Oil, varnish, shellac, lacquer, water-based finishes, and polyurethane each offer a different balance of appearance, application, and protection.
Our Guide to Choosing the Best Wood Finish compares the major types of woodworking finishes so you can choose the right one before you start applying it.
RELATED ARTICLE: How to Choose the Right Finish for Any Project
