You may not have noticed, but the new varnishes are far different from the stuff our grandfathers used. Today’s varnishes are chemically designed to be easy to apply, to give a high gloss finish right from the get-go and to retain that finish for far longer than one season. Unlike spar varnishes, which were designed for use on spars that flex in the wind, these new varnishes will flex with the wood, but do not crack and peel (unless they are applied incorrectly) like the old varnishes did. These varnishes are, frankly, quite spectacular!
It should be noted that the best time to apply varnish is when the temperature is above 60 degrees and below 80 degrees F. Humidity should be about 50% or lower, but be careful if the humidity is within five degrees of the dew point. If temperatures fall, moisture could condense on your newly varnished surface and cause the varnish to fog. If that happens you have to sand it off and start over. Sorry about that!
The oldest of the ‘new’ varnishes and the one I have used the most is Interlux’s Perfection. The two-part varnish with a base (bottom can) and curing agent (top small can) can be either sprayed or brushed. Simply pour the curing agent into the base and stir well to mix both parts.
For bare wood, sand with 100 grit then wipe the job down with thinner 2333N. (Wear gloves.) The first coat is thinned 10% with 2333N and applied with a sponge brush to seal the wood. If the wood has been previously varnished remove any peeling varnish and sand to bare wood with 120 grit. You can overcoat existing varnish but there is no guarantee that both coats will last as long as a Perfection only coating. With the wood sealed, begin applying coats of varnish, sanding between coats with 220 grit sandpaper until you have four or five coats. Job done!
Quantum UV is another impressive two-part varnish with high solids to help deliver a lot of varnish to your brush. It is UV resistant and has good flexibility. Woods tend to expand and contract on a boat and brittle varnishes may crack. The varnish can be sprayed using Quantum Spray Activator, or brushed using Quantum Brushing Activator.
To apply use a bristle or sponge brush. First use one-part brushing reducer to seal the wood before applying three to four coats until the job is done. What you get is a mirror-like finish that will last for two to four seasons. (The varnish hasn’t been around long enough to see how long it really lasts.)
Another top-notch varnish is Awlwood MA. Most Awlgrip products are aimed at the professional applier, and Awlwood MA is meant for professional spray applications. That said, you can buy it at most chandleries and it can easily be applied with a brush. Application of Awlwood is slightly different than the other varnishes in that you need to apply one coat of Awlwood MA Primer which, according to the manufacturer, penetrates the wood to provide greater color retention and improved system adhesion. Before applying Awlwood MA, wipe the wood down with Awlwood MA reducer to remove dust and grease or oil. When the primer coat is dry, but no more than 24 hours after primer application, brush or spray up to eight coats of Awlwood MA gloss for a finish that is tough, and both scratch and crack resistant.
Awlwood MA is best applied to new wood rather than over old varnish. While it is compatible with the Interlux product line, failure of the original varnish could result in failure of the Awlwood finish.