In most shops you’ll likely find at least a few of the following solvents – mineral spirits, paint thinner, paint and varnish remover, turpentine, lacquer thinner, varsol, naphtha (camping stove fuel or white gas), methyl hydrate, acetone, or isoproponol. I often see woodworkers using these solvents without employing any form of personal protection. While I don’t think that we need to get paranoid about the use of solvents in the shop, I do think that we need to remind ourselves that these products can be highly toxic. Most of them are also flammable, and environmental pollutants when not properly disposed of. There is the prospect of short term toxicity when exposed to these products for a brief period of time – for example, the lightheadedness that comes from breathing lacquer thinner fumes. We may not think much of it at the time, but what about after twenty or thirty years of breathing in these fumes? Health and safety experts warn that repeated exposure to toxic solvents may produce general deterioration of health by an accumulation of toxins in one or more organs. Getting into the safety habit when using solvents takes a bit of self-discipline, and a little more time away from our woodworking. But we may well be doing ourselves (and our families) more good than we realize.
One of the easiest things to do when using solvents is to ensure that there is proper ventilation in your shop. Ideally you want to locate your finishing station near a window, which you can open for the duration of the finishing session. Placing a low velocity fan near the window will help move fumes out of the shop. This is particularly important if you work in a small shop.
A disposable dust mask is not at all effective in keeping toxic fumes out of your nasal passages and lungs. Purchase and use an air purifying respirator with an organic vapour cartridge. A half face mask like the North Safety 5400 costs about $40. The cartridges cost $15 and last quite a long time. You can also add an N95 particulate filter ($5) onto the cartridges. This makes for a complete and highly effective dust and vapour protection system.
You should also wear gloves when handling solvents. Nitrile or neoprene gloves (leevalley.com), are an excellent all around choice. Latex and vinyl gloves offer limited protection and are better suited for use when applying finishes and stains. Finally, it goes without saying that you should always wear eye protection in the shop – not just when finishing. High impact safety glasses are a good choice. For maximum eye protection choose chemical splash goggles. Polycarbonate lenses offer better impact resistance than glass or plastic, but they scratch more easily. If you wear prescription glasses you can purchase safety overglasses. Regardless of what you select, don’t buy an inexpensive, ill-fitting pair – they’ll end up in a drawer. Eye protection that meets the Canada Standards Association standard Z94.3, can be had for under $25.
It’s irresponsible to dispose of solvents in the garbage or down the drain. The best solution is to take the liquids to a recycle centre. Most large cities have one. You can also call your local garbage collection or waste disposal service for information. For those who don’t have access to a recycle centre, consider recycling your own. Allow the solid material to settle, and then pour off the thinner. You don’t want to use the thinner again in a finish, but you can use it for cleaning tasks. During the summer you can pour liquids into a shallow pan and allow it to evaporate in the sun – just ensure pets and wildlife don’t have access to the pan. If you have other ways to dispose of solvents let me know, and we’ll print them in upcoming issues of the magazine.
Common Workshop Solvents
By far, the most popular finishes for hobbyist woodworkers are oil based finishes (varnish, polyurethane, oils, varnish/oil blends, stains), water based finishes and stains, and shellac. Just about any of these finishes or stains can be diluted with solvents. Being able to change how quickly a finish dries can go a long way to make wood finishing a less taxing experience. Some solvents enable you to speed up the drying time, while others slow it down. For these three classes of finishes you really only need three solvents.
Most varnishes are on the viscous (thick) side, and can take quite a while to dry. If, like most woodworkers, you don’t have a separate finishing room, the varnished surface will pick up a lot of dust. When brushed on a vertical surface heavy bodied finishes invariably sag. If applied too thick the cured finish takes on a plastic look. The right solvent will speed up the drying time of the varnish so that dust has little time to settle, and when brushing a vertical surface there will be less tendency for the finish to sag and run.
There are two common solvents for oil based finishes; paint thinner and mineral spirits. Mineral spirits contain fewer aromatic solvents (benzene, toluene, xylene) than paint thinners. The higher level of purity is reflected in the price (about $4 per litre for paint thinner and $10 per litre for mineral spirits). Varsol is a registered trademark of Imperial Oil, and has a slightly higher level of purity than mineral spirits. These products are relatively toxic and flammable. When it comes to thinning oil based products you can confidently use any of these three solvents. Naphtha, a product very similar to mineral spirits, is one that you likely have read about in US magazines. The Canadian equivalent is white gas, or camping stove fuel. It has a marginally faster evaporation rate than mineral spirits. Naphtha is very toxic and flammable.
If you have difficulties brushing or ragging on varnish, polyurethane or polymerized tung oil, you can add anywhere from 10% to 50% mineral spirits – the exact amount isn’t critical. Just bear in mind that the more you dilute the oil, the more coats you will have to lay on in order to get adequate protection. Start with about 10% and if you find it’s still too thick, add a bit more mineral spirits. Allow each coat to thoroughly dry between applications.
Water based finishes present their own problems. Unlike varnish, they tend to dry very quickly, making it difficult to maintain a wet edge, which can result in lap marks, or cause bubbles to appear, particularly on a large surface. The quick drying nature of water based finishes also makes them more difficult to brush on than varnish. Fortunately, the solvent for water based finishes is water. Water based finishes are very complex, and it’s best to use distilled water, adding no more than 10%. There are water based retarders that extend the drying time but these are not widely available.
Shellac is a wonderful all purpose finish that is particularly suited for woodworking projects that aren’t subject to a lot of heavy use, or won’t be in contact with alcohol or water. It also makes an excellent sealer coat for any finish. In the US, they use denatured alcohol (ethanol) to dissolve the shellac flakes or thin the shellac. In Canada denatured alcohol is virtually impossible to find. Instead, use isopropanol (isopropyl alcohol), available from feed supply stores and large garden centres. A slight drawback is that isopropanol dries more quickly than denatured alcohol. There are different grades – ensure that the one you use is 99% pure. It’s not the same as gas line antifreeze. Isopropanol is relatively nontoxic and highly flammable. Avoid methyl hydrate (methanol), as it is much more toxic (not only through inhalation but also absorption through the skin). And always wear a suitable respirator when using any solvents.
Keep your woodfinishing safe by properly storing, using and disposing of solvents. Long may you woodwork!