Conversion Varnishes (CV) vs Traditional Lacquers & Other Finishes
Obviously the selection of a finish such as a traditional lacquer, conversion vanish, a polyurethane or other depends on the specific application requirements. Different coatings present advantages and drawbacks briefly discussed below irrespectively of specific products or brands.
Traditional Lacquers
Commonly used on cabinets and cabinet doors for a long time, considered as the best wood finish. Lacquer is a single-component mixture consisting of a pre-catalyzed, nitrocellulose finish that can be sprayed on and air-finished.Because it’s pre-catalyzed, it’s ready to use without mixing in any hardeners. Their low content in solids (12-18%) and quick dry time, require only thin coats which have to be reapplied for proper build and solid film density. Their main benefits compared to other finishes include fast drying ensuring a cleaner finish, fast curing via evaporation, toleration of a variety of climates and their relative low cost. Having a a high VOC content, they can be harmful to the environment and health. Furthermore, due to their low solid content, their film-building properties are poor resulting in a limited scratch resistance and lower durability.
Compared to conversion varnishes, lacquers exhibit significantly less resistance to heat, solvents, acids, and alkalis.
Conversion Varnishes
A conversion varnish (CV) is a chemical-cured, fast-drying finish consisting of two parts: a resin and a hardening agent added to the varnish prior to painting, which provides additional durability when combined with the heat-curing process.
Unlike solvent-based lacquers, CVs are oil- or alkyd-based but dry through solvent evaporation.
Application of a CV can be done in thicker coats than a lacquer, providing a substantial protective layer.This thickness contributes to the enhanced durability of the finish. A CV can be painted with a brush or use a specialized sprayer.
A CV dries to a clear finish, providing a glossy or satin appearance without significantly changing the color. This clarity makes it a popular choice for high-end woodworking and other projects.A lacquer comes in various colors, offering a range of finish options.
Most impotant, a conversion varnish is significantly more durable with a harder and more robust finish than a traditional lacquer. Ther latter is susceptible to scratches and less flexible than CV — and most varnishes — which makes it more prone to cracking. CVs also offer more longevity withstanding a lot of abuse while they significantly resist yellowing. Traditional varnishes and lacquers commonly cause wood components to take an undesirable tint.
A CV is more elastic than lacquer due to its unique chemical curing process. The cross-linking of molecules creates a more resilient finish compared with the brittle nature of lacquer. This increased flexibility is crucial for the finish’s ability to resist the natural expansion and retraction of wood in respective woodworking applications. As a result, its elasticity reduces the chance of cracks at the joints and minimizes the risk of cracking or peeling over time.
The higher solid content of a CV compared to a lacquer (about 40-60% solids by volume) reduces coats and thus time and effort for a good coverage and an appropriate film build. Additionally, a CV is easy to clean while its non-porous surface also helps preventing contaminants from penetrating the finish.
Certain disadvantages (drawbacks) of use of conversion varnishes include:
Complex Application: It requires greater skill in spraying and careful mixing of the two components to ensure the correct ratio. Improper mixing or application leads to poor adhesion, color shifting, and an uneven or cracked finish.
Application Environment: the CV is sensitive to environmental conditions like temperature and humidity. For use consistent temperature conditions must be ensured. Inconsistent conditions during application affect the curing process and final appearance.
Cost: CVs are generally more expensive materials than other finishes.
Curing Time: while conversion varnish will reach almost full hardness fairly quickly, it has a fairly long cure time which can extend your project timeline.
Health Considerations: Some CVs are high in volatile organic compounds (VOCs), which release during application. These can cause environmental and health concerns.
Polyurethane Finishes
Polyurethane is often considered one of the most durable finishes. Polyurethane can resist scratching, heat, alkali, and acids and wear better than many other finishes, including lacquer. It also offers an attractive, protective finish.However, it can yellow over time, especially if in direct sunlight. It also requires sanding in between each coat to ensure proper bonding, and since the dry time is up to 24 hours, it takes quite some time to fully finish a piece. It is also typically brushed on rather than sprayed on, slowing the application even more.
