Inhaling too much of the vapors given off by some wood finishes can cause dizziness. Interestingly, trying to make sense out of all of the varieties of wood finish, finishing techniques, and often contradictory wood finish naming practices can have the same effect. And unless you're an experienced wood finisher, understanding what sets a specialized product like Rockhard Table Top Varnish apart from a more "garden-variety" type of varnish requires a little background information. So, for readers who aren't founts of obscure finishing knowledge, here first are the very basics of varnish:
Varnish is made by cooking together a curing oil and a natural or synthetic resin. A “curing oil” is any oil that turns from a liquid to a solid over time, as a result of exposure to oxygen. For many years, exclusively natural curing oils – such as linseed oil and tung oil - were used to make varnish. More recently, less expensive non-curing oils, after being modified to make them suitable for varnish-making, have become the commonplace ingredient.
There are three types of synthetic resin commonly used in making varnish: phenolic, alkyd and polyurethane. Of the three, you are probably most used to hearing about polyurethane. Polyurethane has a reputation of being tough and reliable, although it’s also reputed to have a less appealing, “plasticy” appearance than other wood finishes. Most of the “polyurethane varnishes” you see in hardware stores, in fact, are actually alkyd varnish – the “workhorse” of the varnish family - modified with polyurethane resin. Phenolic resin is more expensive, but makes for an exceptionally hard and durable varnish with excellent resistance to solvents and moisture.
The ratio of resin to oil in a varnish also plays a major role in how it will behave as a finish, and hence what it will best suited for. A “long-oil” varnish is one with a high ration of oil to resin, and as a result, tends to produce a less hard and brittle finish, and to retain its flexibility. “Spar” varnish is and example of a long-oil varnish. Usually made with phenolic resin, spar varnish is designed to meet the outdoor elements with a suitably moisture resistant and flexible finish.
Now, why should you use Rockhard Table Top Varnish for your table tops instead of something else? Behlen Rockhard is a short-oil varnish, meaning that it has a low ration of oil to resin. High resin-content varnishes produce a harder, more wear resistant finish, suitable for surfaces that take a lot of use - like a table top. Along with that, Rockhard is made with tough, moisture and solvent resistant phenolic resin and natural, harder-curing oils. The result is an extremely hard, scratch resistant surface that will also stand up extremely well to just about any kind of household spill that you can throw at it.
There's a good basic explaination of how to use Rockhard Table Top Varnish in furniture finishing expert Sal Marino's article, "Finishing Oily Woods". For a quick tour of the most often used wood finishes, read Rockler's Finishing Comparison Guide. And for an in-depth look at all things finishing, treat yourself to a copy of one of the most respected books ever written on the subject: Bob Flexner's Understanding Wood Finishing.