Varnish - Canadian Woodworking Magazine

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Varnish



For many, varnish is the king of finishes. It produces a clear finish with a lot of depth; has superior water, abrasion, solvent, and heat resistance; is relatively easy to apply; and has good rubbing and polishing qualities. On the down side, some varnishes yellow with age; they are notorious for becoming embedded with dust (because they cure slowly); and they are difficult to repair. Nonetheless, the benefits of varnish far outweigh its drawbacks.
 
The Long and Short Of It
Varnish is made by cooking oil with a resin. The oil can be linseed, tung, soya, safflower, or the like. The resins can be natural (made from pine tree sap or gum turpentine), or synthetic (made with phenolic, alkyd, or polyurethane resins. Metallic dryers are also added.

Varnish that has a lot of oil added to it is called long oil varnish, and sold as spar, marine or outdoor varnish. More oil makes the varnish more flexible. Short oil varnish has less oil added, which makes it harder. Short oil varnish is the typical varnish you use on furniture and interior trim work.

Varnishes are 'reactive' film finishes. As the thinner (i.e. mineral spirits or naphtha) in varnish evaporates, the resin molecules react with oxygen to bond together in a process called polymerization. Because varnish reacts with oxygen in the air, it cures from the top down, so you want to keep each layer thin, and you want to ensure that the previous coat is fully cured before you apply a new coat. Because the layers of varnish don't fuse together once they've cured, you need to lightly sand between coats. How many coats? Generally three or four are all you need.
 
Choices, Choices
There are lots of different brands of varnish for you to choose from. Most of what you'll find at your hardware store is polyurethane, which comes in a gloss, semi-gloss, and satin sheen, and is available in pint, quart, and gallon quantities. Although most varnishes can be either brushed or wiped on, some are brush only. You can also buy varnish in aerosol cans, which is particularly handy for finishing small pieces or for touch up work. It's a good idea to buy varnish in a quantity that you can use in a short period of time, as varnish will begin to skim over after a while. Once you've found a brand that you like, it's good practice to stick with that brand.
 

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From left to right – Circa 1850 Paste Varnish, Circa 1850 Polyurethane, and Circa 1850 Marine Varnish
 
The brand that I have been using for the past six months is Circa 1850, made by a Canadian company, Swing Paints. The Fast Dry Polyurethane is my favourite finish. It has an amber color, is quite thin (which seems to help it flow on easily), and dries in about 3 hours. It produces a very durable finish, which rubs out nicely.

If you're looking for a hand rubbed finish with much better protection than you can get from Tung or Danish oils, then try Circa 1850 Paste Varnish. This is a gelled polyurethane varnish that you rub on with a cloth. It dries in four hours, and you can lay four or five coats for a decent level of protection. An excellent product for furniture that won't see a lot of day-to-day use.

For outdoor furniture you can't go wrong with Circa 1850 Marine Varnish. It contains UV filters as well as a fungicide and mildewcide.
 

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Applying
To get a really great varnish finish you need the right environment and the right tools. Without getting too fanatical, it's best to work in a dust-free room that isn't too cold or damp (both slow down curing time). Make sure you've raised the grain and wiped all the dust off your work piece and work table. You might want to do your finishing at the end of the work day, so you won't be introducing new dust into the air, or later in the evening after the dust has settled.

If you're new at varnishing, you'll find it a lot easier to wipe it on. You can buy a wiping varnish, or you can make your own, by adding two to three parts naphtha (camping fuel), or mineral spirits to one part varnish. Naphtha will evaporate more quickly than mineral spirits (i.e. the finish will dry faster). Use a clean lint free rag to wipe the varnish on. Don't worry if you miss a spot, you'll cover it with the next application. Be sure that you don't wipe over a wet area, or you'll muck up the finish. After four or five hours you can wipe on another coat. If you dilute the varnish with a lot of thinner you'll need to apply more coats (eight, nine, even ten) in order to build up a protective finish, as each layer you apply is micro thin. When wiping on varnish you don't have to worry much about dust, as the thin coats will dry pretty quickly. If you notice any dust very gently sand with 320 or 400 grit paper.

The secret to brushing varnish on is getting a good brush, learning how to use it, and keeping it clean after each use. For the past six months I've been using a Lily Varnish Omega brush. This is a natural bristle brush, slightly tapered with fine flagged ends. Extremely well made, and available in seven widths, from 20 to 100 mm. It holds varnish well, and hasn't dropped a single hair since I've been using it. To maximize the life of your brush make sure you clean it after each use, and properly store it. Wash it well in mineral spirits, then rinse it out with lacquer thinner, followed by a wash in soap and water. Dry it out with a paper towel, rub a couple of drops of mineral oil on the bristles, comb out the hairs, and finally wrap it in absorbent paper. Don't use your varnish brush for applying other types of finish!

The best way to learn how to brush varnish is to practice brushing it on scrap plywood. Use long steady brush strokes with the brush held close to vertical, working in the direction of the grain. If you notice bubbles you can "tip-off" your brush strokes by holding the brush vertical and drawing the tip lightly across the surface. But only do this if you notice the bubbles right away. Varnish starts to skin over quickly, and you'll only muck up the finish if you brush over it once skimming starts. Don't rush your brushing. Take things slowly, make sure you've got good lighting, and allow each coat to dry thoroughly before applying the next coat. It's a good idea to thin the first coat with naphtha (half and half), which will act as a sanding sealer. Alternatively, you can use de-waxed shellac as the sealer. After you've applied a couple of coats you can very lightly sand out any dust nibs with 220 grit paper. In general, three or four coats of varnish are all you need. To obtain a finish with maximum sheen and gloss, you have to rub out the finish. I will cover rubbing out the finish in a future article.

For large items, such as cabinets, consider varnishing in several stages. Try positioning your project so that you're only brushing horizontal surfaces. It takes longer, but you'll avoid the problem of sagging varnish. You can also finish parts of a project, such as panels, bottoms, and backs before final glue-up. Carefully applied masking tape will prevent the finish from covering those parts to be glued.


Sources:
Varnish:
www.swingpaints.com or 514.932.2157
Omega brushes: 800-332-1556 www.finepaintsofeurope.com