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Water-Based Polyurethane, Stains, and Other Finishes

By HHI Staff

Polyurethane finishes use polyurethane resin as a binder. However, because this particular resin is expensive, its often mixed with other synthetic binders such as acrylic resins. In most cases, polyurethane finishes are clear (some have stains or solid pigments added) and they work well at protecting wood surfaces.


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However, you should be aware that there are both oil- and water-based polyurethane clear finishes. Of the two, the oil-based types should be avoided. This is because their solvents are very strong-smelling and potentially harmful when the finish is being applied and while it’s curing. While oil-based polyurethanes are admittedly very durable finishes, some very chemically-sensitive persons have found that, even many months after application—long after they should have been cured—they’re still bothersome.


Fortunately, the relatively new water-based polyurethane finishes can be used instead of the oil-based versions. These products tend to dry quickly and generally have little or no residual odor after less than a week. As a result, many very chemically sensitive individuals find that water-based polyurethane finishes are quite tolerable. Other advantages to using these particular products include the fact that they’re commonly stocked in local stores, and they are lower in cost than many other types of alternative, clear finishes. Their big drawback is their wearablity. Some brands warn that they’re “not for use in heavy traffic areas.” Therefore, before purchasing any water-based polyurethane product, read labels carefully to know what you’re getting before you apply it. You should also consider what sheen (light reflectablity) you want. Most brands are made with either a satin or gloss finish, and some have other sheens available.

Acrylic Finishes and Sealants

Clear acrylic finishes create a hard, durable, low-odor coating primarily on woods. Yet, when they’re wet and during their drying period, some formulations are somewhat more odorous than the water-based polyurethane finishes. This is true despite their being water-based products. Chemically sensitive individuals often report that some clear acrylic finishes take up to two months before they are tolerable to them. After that, they often become nearly odorless.


(Note: Many sensitive people find that such sealers help, but not enough to make a bothersome material tolerable. In other words, sealants tend to be imperfect.)

Shellac and Shellac Sealants

Shellac is an ancient finish, being first developed in the Far East. It uses purified lac resin (a secretion deposited on tree branches by female lac insects) as its binding agent. Lac—and therefore, shellac—varies in color from pale, translucent yellow to dark orange, depending on the variety of tree the lac insects live on. As it turns out, shellac produces a fairly tough finish that is commonly used to coat wood. However, white discolorations can manifest themselves rather quickly if water gets on a shellacked surface.


It’s important to understand that shellac is neither a water-based, nor an oil-based, product. Instead, it uses alcohol as its vehicle. Therefore, denatured alcohol is necessary for cleaning up. (Denatured alcohol is a common thinner made simply of alcohol altered in such a manner as to make it undrinkable.) In fact, because of the alcohol content in shellac, it’s quite flammable. It’s also extremely odorous when wet. Fortunately, the alcohol evaporates very quickly, and when the finish is completely dry, shellacked items are often tolerable to many sensitive individuals. However, some people have noted that, sometimes, a noticeable, and bothersome, “shellacky” odor will persist.


Most people consider shellac to be a completely pure and natural finish. However, most brands today contain a few additives—sometimes synthetic ones.

Penetrating-Oil Finishes

Some individuals may want to try a natural penetrating-oil finish on their wood items. A penetrating-oil finish doesn’t leave a thin, hard coating on wood surfaces, but instead it penetrates down for some distance into a piece and saturates the very fibers of the wood itself. Therefore, if the wood’s surface ever becomes scratched or abraded, you can simply apply more oil to the damaged area and it will blend in without the need for stripping and refinishing.


However, there is a downside. Many of the oils used as wood finishes are fairly odorous when applied. And, they can remain quite odorous for a considerable amount of time afterwards as well. In fact, their smells could continue to be bothersome for up to several months—or longer. Of course, this depends on the specific oil, wood, and your personal tolerance but, in general, oil finishes are not well tolerated by chemically-sensitive people.


Two of the more popular natural penetrating oils are tung oil (derived from the nuts of tung-oil trees) and linseed oil (derived from flax seeds). Of these, tung oil is not recommended. This is because it’s been implicated in suppressing immune system functions, as well as reactivating chronic Epstein-Barr virus infections. However, there are certainly other oils available.


Of all the oils, probably the most commonly used one is linseed. Linseed oil, which is naturally anti-bacterial, is available in two varieties: raw and boiled. While raw linseed oil will not dry properly when applied to wood, boiled linseed oil will. In the past, many manufacturers simply heated raw linseed oil to give it drying properties but, today, most “boiled” linseed oil has not been heat-processed at all. Instead, manufacturers add toxic heavy-metal additives, such as lead acetate or cobalt manganese, to aid in drying. Fortunately, there are types of boiled linseed oil still being made without these types of additives.


One final note, if you find you need to use a penetrating oil finish on salad bowls or kitchen-knife handles, consider using virgin olive oil. Olive oil is not only nontoxic, it’s also resistant to becoming rancid.

Wax Finishes

Waxes such as carnuba wax (derived from the plant waxes found on certain palm leaves) and beeswax (derived from honeycombs) are sometimes used to create clear, natural finishes on wood. Like penetrating oils, waxes provide protection that can be easily repaired if a scratched area should develop. This is because they penetrate and saturate wood rather than form a thin brittle layer that lies on the surface. For some people, natural waxes can be good wood-finishing choices.


However, it’s important to know that many natural waxes are somewhat hard in consistency. Therefore, these pure waxes are heated or mixed with denatured alcohol, turpentine, or another volatile solvent to make them more workable. Of course, solvents could make a wax application intolerable to many chemically sensitive individuals. However, it should be noted that, once the added solvent has completely evaporated, the finish could be quite acceptable for these very same people. Of more concern are packaged wax formulations which may have paint thinners or similar solvents added, as well as other odorous ingredients such as oils and resins. Therefore, make sure to check the ingredients of any wax product before purchasing it, if such ingredients could be a problem for you. Remember: Testing is important, especially if you’re chemically sensitive.


A long-time, popular wax choice is beeswax. But it should mentioned that beeswax tends to have a somewhat flowery odor. Although some people may find this attractive, others may find it bothersome. You can generally purchase pure beeswax from local beekeepers. To find a beekeeper, check your local classified telephone directory.


Carnuba wax (a tree wax) is also popular for finishing wood. Often, you’ll be able to find carnuba wax in your local hardware store.

Water Glass

Water glass is a term applied to certain water-soluble sodium silicate compounds. Interestingly, these compounds have a similar chemical composition to ordinary window glass. As it turns out, water-glass solutions used as finishes are transparent and virtually odor-free. This is also true when they’re wet. Not surprisingly, these are commonly very tolerable products for sensitive individuals.


Water glass was once a popular product. However, since World War II, synthetic sealants have nearly replaced it. But water glass is still sometimes used as an effective grout and concrete sealer. As it turns out, when water glass comes into contact with the calcium (and certain other substances) in these materials, a chemical reaction takes place. The result is the creation of a hard, clear, crystalline surface that’s very durable. Water glass can also be used to protect your ceramic-tile grout joints by applying it carefully to the dry grout joints—not the tile—with a small artist’s paint brush.


It should be noted that water glass should not be applied to a concrete floor—if you ever plan to apply ceramic tile to it later. This is because the sealed surface would be nonporous. As a result, it would prevent the adhesion of the ceramic-tile mortar. Another consideration to keep in mind is not to use too much water glass when you’re applying it. A little goes a long way, and applying too much could result in a film that might peel off.


Many woods look interesting and attractive just as they are. And by leaving them natural, you’ll avoid using at least one potentially bothersome product—wood stain. However, if you decide you really want to use a stain anyway, following is some basic information about stains that you may find useful.


Wood stains are generally available in either oil-based or water-based formulas. Oil-based types often produce richer, deeper tones than their water-based counterparts. Unfortunately, they’re also usually somewhat more odorous. They also require paint thinner or turpentine for cleanup.


While water-based stains generally don’t appear as rich-looking, they do have other distinct advantages. For example, they contain fewer VOCs (volatile organic compounds) and they don’t need noxious solvents for cleanup. As a result, although water-based stains are not odor-free, they’re less bothersome than their oil-based counterparts.


If you want to use a water-based stain, it’s best to test several brands for appearance and personal tolerance. Of course, tolerance testing is always essential for chemically sensitive persons. By the way, it is best to stain a sample piece of wood, as well as apply two coats of clear finish, then test for tolerability. This is important because the clear finish will often seal in any minor odors from the stain. But you won’t know for sure until you’ve actually tested the sample.


(This article is from the archives of the original Healthy House Institute, and the information was believed accurate at the time of writing.)

(Note: The views expressed in this article are those of the author, and do not necessarily represent those of The Healthy House Institute, LLC.)


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Water-Based Polyurethane, Stains, and Other Finishes:  Created on June 2nd, 2008.  Last Modified on February 27th, 2011


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