It is especially important to varnish all around a workpiece, particularly if it is made of teak and installed on boats because any place where moisture can enter under the edge of the varnish will eventually cause the finish to lift. You will need to support your work in a steady manner so you can push the brush against it without your workpiece giving way and collapsing.
If there are holes in the workpieces, it is a great idea to thread a bolt or screw into the holes so you can hang the work. Hanging your work is ideal but you need to make sure that you have enough supports to keep your work from swinging around as you try to press your brush against it.
An alternative would be to use triangular pieces of scrap wood to lay underneath so that only the pointed surface touches your work. Or, use screw points (the “bed of nails” approach) that are driven up through scraps of wood. Just be sure to use enough points so that the work is not wobbly, and move the points of contact around with each subsequent coat of varnish.
Once you are ready to lay on the varnish, you will need a light source that you can place at a remote distance so you can see across the surface of the wood and notice any gaps or “holidays” in your work as you lay on the finish. A window or a Spotlight can be used as long as there is strong enough light to make it clear to you as you work. You will want to minimize the brush strokes that you use in order to keep bubbles to a minimum, so don’t mop the finish around, and always plan to keep a “wet edge” in your work. This allows you to brush backwards into the wet edge of the finish so brush marks have a chance to settle out.
Try to “feather’ your brush as you brush it backwards into the wet edge, which means lifting the brush at an angle as it leaves the existing wet edge. It takes a bit of practice, which is another reason why it is a good idea to practice with each coat and pretend that it is your final coat.
The amount of varnish that you lay on the surface can be very difficult to gauge, but it should be as much as possible without causing excessive sags in the dried coat that need to be sanded out. Don’t worry about it at first, because you will learn as you go and you will apply the appropriate amount by the time you reach the final stages. Just remember to “flow” the varnish out of the can onto the surface of the wood and use as few brush strokes as possible in the process.
Please note that marine “spar varnish” tends to be softer than furniture or floor varnish, particularly in the sun or when it is very hot. Some brands will even feel “sticky” when they are hot, long after they are fully cured. This is a natural effect that allows the varnish to expand along with the wood in the extreme marine environment. Modern spar varnishes also have UV inhibitors added to block the damaging effects of ultraviolet radiation from the sun. For these reasons, you should never use floor varnish outside on your boat and it is not recommended to use spar varnish on the floors of your house or on furniture that will be subjected to long periods of sitting unless you don’t mind seeing the seat of your pants permanently imprinted in your priceless heirloom.
The choice of which brand of varnish to use is a very personal one, but it is always a good idea to stick with the same brand throughout the process of building up the finish. Once the varnish has completely dried, you can overcoat it with virtually any other brand that you desire, but you may encounter incompatibility issues during the initial stages when the underlying coats are not completely cured. Also, if you try to mix epoxy as an underlayer and overcoat it with varnish, make sure that you are using compatible products.