Clear finishes protect wood from wear, moisture, and aging, but they can degrade the environment—in your home and elsewhere. When selecting a clear finish for wood finishing or refinishing, we recommend considering the environmental impact of its manufacture and disposal, its effect on indoor air quality, and its durability.

The environmental impact of clear finish manufacture and disposal ranges from high (for the energy-intensive and polluting manufacture of petroleum-based solvents) to low (for the extraction of natural oil from tung tree nuts). All clear finishes must be disposed of as hazardous waste, so it’s best to buy only the amount you need.

Like paints, clear finishes can contain high levels of volatile organic compounds (VOCs), which contribute to air pollution and can cause health problems. (See About VOCs for more information.) Finishes can have a greater effect than paint on your home’s air quality, however, because they must be reapplied more frequently on high-use surfaces like floors, tables, and chairs. Toxic and polluting ingredients such as toluene and xylene are common solvents; carcinogens such as arsenic, beryllium, and cadmium are sometimes used as drying agents in linseed oil; and toxic glycol ethers may be used as solvents in many water-based sealers.

All clear finishes are made of a carrier, or solvent, which preserves the finish liquid in the container and evaporates as the finish dries, and a binder, or resin, which protects the surface. Finishes may also contain additives to speed drying or provide fungicidal properties. All these elements contribute to a finish’s environmental impact.

Solvents can be derived from petroleum-based or synthetic materials as well as from materials as simple as linseed oil or water, and can vary within a type of finish: some types of lacquer, for example, use water as a solvent while others use oil. The binder determines a finish’s function, durability, and category (lacquer, natural oils, shellac, and so on). Additives may be toxic, though not all are.

Clear finishes vary in their durability and ability to protect wood from heat, water, and chemicals. Lacquer, shellac, varnish, and water-based sealers coat wood, forming a protective layer on the surface; natural oil sealers penetrate wood, prolonging the wood’s life but leaving the surface susceptible to scuffs and dirt.

Strictly speaking, any finish that forms a film on wood can be used as a sealer. Some coatings are so good at this task by themselves that they are called “self-sealing” finishes. Other finishes are not, and they benefit from special sealers.

Shellac and oil-based finishes, (including Danish oil, varnish, and polyurethane) work so well by themselves that they do not require any special sealer under them. Some finishers prefer to thin the first coat of these materials to make them dry quicker or sand easier, but that is strictly a personal choice.

Lacquer and waterbased coatings, on the other hand, work better over sealer. The right sealer will lock in contaminating oils and waxes, reduce the number of coats needed by preventing excessive absorption, improve adhesion, and reduce grain raising, especially under waterbased coatings.