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RickW

Types of Varnish

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Which varnish should I use?  A traditional spar varnish, a single urethane, or a two part urethane?

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Choosing The Right Varnish

Quality marine varnishes fall into 2 basic categories, modern hard varnishes and traditional spar varnishes. The choice boils down to two main considerations: How stable is the wood you are coating? If it is prone to movement, such as a spar, old clinker, or carvel planked boat, traditional varnish is the right choice. If the piece is more stable and inert, a harder modern finish is also an option.

While modern finishes resist wear better, they are also harder to remove when you recoat. Some require strict temperatures and conditions for application that may not suit a boat out in the open. Traditional marine varnishes apply easily but typically have a longer cure time. Higher tung oil content provides a beautiful golden hue and that almost-wet appearing gloss. Traditional varnish builds on top of wood surface with minimal penetration, making it easiest to remove when the time comes.

Monourethanes & single polyurethanes combine the best of old and new: they yield a harder finish that cures quicker via moisture content in the wood. The finish can be polished and is easier to remove than a two-part. Cure time is often optimized to allow several applications in one day. These hybrids also contain oils to create a more pliable coating with the traditional look.

Two-part polyurethanes and epoxy varnishes produce the most durable, scratch resistant finish available and done properly yield long lasting beauty. Application is more challenging, as they require specific temperatures and cannot be exposed to rain or dew during the curing window. These coatings penetrate into the wood, creating a superior coating capable of lasting several seasons but require sanding to remove. This is worth considering if it's a classic boat with irreplaceable woodwork. Best used in controlled indoor environment on very stable wood surfaces.

Key to achieving a professional looking finish is a high quality varnish brush, with natural bristles like badger hair. A badger hair brush has thick bristles to load more varnish. Since a good varnish will self-level, or flow out evenly across the surface, this thicker brush lets the varnish level out as designed. The key is to start from one section and maintain the wet edge without going back over the work. You will achieve better coverage with no visible brush strokes. If you are applying a modern clear coating treatment such as a 2-part poly, a thinner brush is preferable. Before applying, be sure to shake out any loose bristles by gently and rapidly wiping across a clean hand. Another option for quick, no cleanup jobs are disposable foam brushes. They are cheap, convenient and will not leave bristles behind. Foam brushes don't leave behind brush strokes, a plus if you are inexperienced.

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Most types of varnish are available in different finishes, including matte, glossy, satin, etc. Aerosol varnishesAerosol varnishes are particularly easy to use for acrylic paintings. They’re normally applied vertically in thin layers and used in a well-ventilated space. Varnishes for oil paintWhen you varnish an oil painting it smoothes out the finish on the work and protects it from damage. Varnish is a stronger coating than the layer of dried paint which remains fragile even when it’s hardened. If you varnish a painting before it’s fully dry a number of problems may occur like the varnish may crack or soak into the paint which makes it impossible to remove ormake the painting permanently sticky.

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