| Finishers always should wear personal protective gear whenever spraying conversion varnish or other 'super' coatings and the finishing area must meet certain local codes, including fire codes, in order to spray these coatings. |
In recent years, the so-called "super" high-performance coatings have been taking over the wood finishing industry. But what, exactly, are they? This article will give you a quick overview, with some in-depth information about one of the most popular ones, conversion varnish.
All of the super coatings are reactive, which in essence means that these chemically improved coatings will not dissolve once they are fully cured. They become very hard and are extremely durable and chemical-resistant to most household products.
These coatings are known generally as "post-cats" because they are catalyzed just before they are sprayed, while the "pre-catalyzed" lacquers -- which are not comparable to any of the super coatings -- as a rule are catalyzed during the manufacturing process and then shipped.
However, recently some manufacturers have stopped adding the catalyst into the lacquer coating and are sending the catalyst along with the coating to allow the finisher to add it into the coating just before he starts to spray.
Conversion varnish is a coating that contains a synthetic alkyd resin, plus several solvents and an acid catalyst. When these components are mixed together, the result is a chemical reaction that triggers the molecules to start to crosslink. This means that the molecules in these chemicals become larger in size and start to overlap each other, which causes the coating to crosslink and chemically cure.
The main features of conversion varnish are:
One coat of conversion varnish can equal four coats of some of the single coatings. This allows you to do high-build finishes with fewer coats, and that attribute alone can save finishers a lot of time, labor and money.
How to Use Them
Usually, a vinyl sealer is used first to seal the wood and protect against high- moisture areas, like around a kitchen sink or bathroom vanities. Once the sealer has dried, the conversion varnish is catalyzed, using the proper amount of catalyst.
It is important to catalyze only enough coating needed for the work ready to finish at hand. Any excess coating that is not used may not be saved for another day. It also is important to follow exactly the instructions of the material supply company.
Once the catalyst is added to the coating, immediately start to mix the two components and continue until the catalyst has thoroughly dissolved. Let the coating dwell for about 15 minutes in order for the chemical reaction to begin. Then apply a full wet coat and wait about an hour. If sanding is needed, lightly scuff sand, clean the sanding dust, apply a second coat and allow it to cure.
I strongly recommend that you buy all of your conversion varnish materials from the same manufacturer or supplier. It is not a good practice to buy from separate companies, as this could cause problems in the final coating.
Another suggestion: If you do not have a moisture meter, buy one. You should check the moisture content in the wood before you start finishing, as high moisture can cause problems.
Be Careful When Using These Coatings
Not every conversion varnish is exactly the same. So it is important that you get a product data sheet from the manufacturer or supplier to know how the individual product you are buying works. Also, be sure to read the instructions on the labels and follow them to achieve good results.
Besides conversion varnish, other types of super finishes are two-part urethane, polyester, epoxy, UV-cured coating, acrylic/epoxy, acrylic/ polyurethane and powder coating. With any of these coatings, a finisher always should use proper personal protective gear. In addition, the finishing shop must be compliant and meet the town/city codes, including fire codes, for the particular area. These coatings involve serious chemicals. So you must do some homework and understand all the pros and cons if you consider using them.
As I mentioned above, conversion varnishes have various pot lives, depending on the individual manufacturer. Once the coating is catalyzed, it begins crosslinking. It is important not to go beyond the manufacturer's time recommendations, as that could cause serious problems.
Likewise, never add more catalyst than is suggested by the manufacturer; do exactly what is prescribed -- nothing more or less.
Also, check the manufacturerâs recommendations about how many coats you can apply; some may recommend only one coat of sealer and one coat of conversion varnish, while others may list the amount in dry mils and others will have different application schedules. Be sure you know yours.
Yet another consideration is shop temperature. In order to use conversion varnish, a shop should be able to control its ambient temperature, because lower temperatures will affect this coating and may cause problems.
Conversion varnish is used by many furniture, kitchen cabinet and bathroom vanity manufacturers and by architectural finishing shops for interior woodwork, although they may also use one of the other super coatings for certain applications. If you are looking for a coating that is very hard, extremely durable, chemical-resistant and water clear, conversion varnish may be your answer. But follow the caveats listed above to ensure problem-free results.
Mac Simmons is a freelance writer and 50-year veteran of the furniture finishing, refinishing and restoration trades. He has written articles for woodworking magazines in the U.S., U.K., Canada, Germany and Australia and just introduced two new finishing e-books on CD for $24.95 each. For information or orders, write Mac Simmons, Box 121, Massapequa, NY 11758. Other questions may be directed to him via e-mail c/o [email protected]
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