Last time I wrote about the dangers of furniture, floor, and wall finishes containing volatile organic compounds (VOCs) that can produce a number of physical problems, including eye and skin irritation, lung and breathing problems, headaches, nausea, muscle weakness, and liver and kidney damage. VOC levels can be 10 times higher indoors than outdoors, with numbers rising up to 1,000 times higher immediately following application of a new coat of finish.
So what can we use without killing ourselves? Let’s look at the commonly available products.
In today’s common usage, “varnish” means a mix of drying oil and a natural or artificial resin that is cooked (often with an inert metal catalyst) to make a clear finish that is typically used indoors. Varnish cures by chemical reaction and is known for good resistance to heat, solvents, and water. Alkyd and polyurethane varnishes, however, may contain high VOCs. Water-based varnishes using polyurethane or acrylic polymers have been developed that emit lower VOCs, so water-based polyurethane is probably your best bet here.
Water-based finishes offer minimal solvent fumes, easy cleanup, and good scuff resistance, but they may raise raw wood grain. I’ve used water-based urethane on our dining room table and it seems impervious to most spills. The first time I used it, I thought something was wrong with it because it looks milky on application, but it dries clear.
In its pure form, shellac is a natural resin secreted by the lac insect, found mostly in India and Thailand. Shellac cures as its solvent – alcohol – evaporates. Although it creates a brilliant shine, shellac’s uses are limited because of its susceptibility to damage from liquids and heat. However, shellac is useful for any surfaces that won’t need to be washed and for touch-ups because it bonds well to most other finishes. Because it is a mostly natural product, shellac is also a good choice.
Shellac is one of the few historically appropriate finishes (including casein paint, spar varnishes, boiled linseed oil and lacquer) for early 20th-century hardwood floors, and wooden wall and ceiling paneling. Shellac is non-toxic when it is dry according to the A.F. Suter Co. (one of the world leaders in shellac production) and is used in candy and fruit coatings and by pharmaceutical companies as a pill coating.
Lacquer is a clear finish best suited for accenting wood grain.
Lacquer thinner is a blend of solvents, which may include ketones and esters, alcohols, and fast-evaporating toxic hydrocarbons such as toluene or xylene.
Like shellac, lacquer cures by evaporation. Without a clear protective coating, it is easily scratched and susceptible to water damage. Lacquer gives that super glossy coating but, because it makes wood look like it is encased in plastic, is best applied with a spray, and is toxic. I don’t use it.
Tung and linseed oils are penetrating finishes that cure by absorbing oxygen from the air, a process that strengthens the finish. Tung oil is derived from the nuts of trees that are native to Asia, and it is believed to have originated in ancient China and appears in the writings of Confucius from about 400 B.C. When applied in many fine coats over wood, tung oil slowly cures to a satin “wetted wood” look with a slight golden tint. It resists water better than any other pure oil finish, though it still provides little protection against scratches.
Tung oil has become popular as an environmentally friendly wood finish, but it should be noted that many products labeled as “tung oil finishes” are deceptively labeled: polymerized oils, wiping varnishes, and oil/varnish blends have all been known to be sold as tung oil finishes (sometimes containing no tung oil at all), and all the above contain solvents and/or chemical driers. Product packaging will usually clearly state if it is pure tung oil, so there is a good chance you will be buying something else if the sales literature is vague.
Linseed oil, extracted from flax seeds, is a common carrier used in oil paint, but can be used as finish on its own. When used as a wood finish, linseed oil dries slowly. It does not cover the surface as varnish does, but soaks into the pores, leaving a low-gloss finish that shows off the grain of the wood. A linseed oil finish is easily repaired, but it provides no significant barrier against scratching. Water will penetrate a linseed oil finish in minutes, so it should not be used outdoors. Garden furniture treated with linseed oil may develop mildew.
Today, most products labeled as “boiled linseed oil” are a combination of raw linseed oil, petroleum-based solvent, and metallic dryers (catalysts to accelerate drying). The use of these metallic dryers makes boiled linseed oil inedible.
A pile of rags soaked with linseed oil is a severe fire hazard because they may oxidize and eventually become hot enough to spontaneously burst into flame. This is not something you want in your basement or storage room.
More and more homeowners, builders, and architects are turning to penetrating stains instead of paints, especially for exterior use. Unlike paints that form a film on the surface, these stains soak into the wood, accenting the wood grain rather than hiding it. Stains become part of the wood, which helps to prevent the cracking, peeling, chipping, or blistering that commonly occurs with paints.
Interior stains, used for furniture and woodwork, come in either pigmented or dye categories. Both can have an oil, synthetic, or water base. Pigmented stains are designed to change the colour of a surface without concealing the grain pattern or surface texture, and they can range in colour from almost clear to semi-transparent. They are easily applied with a brush or a rag, and are then wiped off to control the depth of the stain. An oil or polyurethane finish is often mixed with the stain, so the do-it-yourselfer can complete the staining and finishing job in one step.
Remember, though, that the more the product is touted as “fast drying” or “one-step application,” the more likely it is to contain chemicals.
Our house contains fir beams and a pine ceiling. We tried many different products, but ended up with boiled linseed oil. It is easy to apply, you can start and stop anywhere at any time, it is less toxic, provides a warm tone, and beautifully highlights grain. However, it is not a protective coating.
If you want to maintain a perfectly pristine interior, you have no choice but to hold your breath and encase everything in plastic and chemicals.