Different Types of Varnish Should be Used for Outdoor and Indoor Purposes
Varnish is a type of wood finish that is used to provide a protective barrier. After it is applied and dried, varnish provides a resistance to water, heat, chemicals and solvents.
Two Types of Varnish
Varnish can be placed into one of two categories: Spar and Traditional.
Spar is known by a few different names:
- Long-Oil Varnish
- Exterior Varnish
- Marine Varnish
Spar is the recommended varnish for a variety of outdoor uses. The primary reasons that this type is better for outdoor wood is that it remains flexible over time, it has additional alkyd resins for UV stability, and it is more flexible. Outdoor furniture is typically finished with Spar.
Just like spar, traditional varnish is also known by a couple of different names:
- Short-Oil Varnish
- Interior Varnish
Traditional varnish dries hard and brittle but is scratch resistant. It is also resistant to yellowing over time. This type of varnish is usually used on furniture that will not be placed outdoors.
What is Varnish Made From?
True varnish is made from plant based resins and oils. Synthetic varnish is made from hard, durable synthetic resins. When made from synthetic materials, its classification is usually polyurethane or urethane. When a varnish is water-based, it is not a true varnish and is considered non-traditional and synthetic.
True varnish is the most durable type of finish that can be applied to furniture. It provides the greatest barrier to protect the wood from water, chemicals, and other sources of damage.
Types of Spar and Traditional Varnish
There are three types of varnish that fall under the spar and traditional categories:
- Brushing Varnish
- Two-Component Catalyzed Varnish
- Rubbing Varnish
Standard varnish is the most common type. Most people are familiar with standard varnish because it is the easiest to apply. It involves using either a brush or a spray for application. This type of varnish dries very slowly and can run or sag if applied too thick. It can take up to two weeks or more to dry to a hard finish. Standard varnish comes in several sheens: matte, satin, semi-gloss and full gloss.
Two-component catalyzed varnish is primarily used on indoor cabinets. It provides a very durable finish to the wood. It cannot be applied with a brush. A sprayer must be used. This type of varnish dries fast. It also reacts with polyurethane or water based finishes. Two-component catalyzed varnish is a “borderline” synthetic product and considered a top-of-line finish for many wood applications. This type of varnish comes in two sheens: satin and gloss.
Rubbing varnish is a gel. It must be hand-rubbed onto a wood surface with a soft cotton cloth. This type of varnish is slow to harden and the sheen it produces depends on the number of layers. A high number of layers will produce a higher sheen. Resulting sheen is satin to semi-gloss.
Varnish Does Not Require a Sanding Sealer
There are many positive aspects associated with varnish.
- Standard varnish can be used over any type of wood stain.
- Varnish is non-reactive with other finishes.
- Varnish acts as its own sanding sealer.
- Varnish does not require any additional products to act as a “sandable primer” for the smoothest finish. Simply sand the varnish when dry, wipe off the dust and recoat.