Spar varnish (occasionally also called boat varnish or yacht varnish) is a

wood-finishing Wood finishing refers to the process of refining or protecting a wooden surface, especially in the production of furniture where typically it represents between 5 and 30% of manufacturing costs. Finishing is the final step of the manufacturing ...

varnish Varnish is a clear transparent hard protective coating or film. It is not a stain. It usually has a yellowish shade from the manufacturing process and materials used, but it may also be pigmented as desired, and is sold commercially in various ...

, originally developed for coating the

spar SPAR, originally DESPAR, styled as DE SPAR, is a Dutch multinational that provides branding, supplies and support services for independently owned and operated food retail stores. It was founded in the Netherlands in 1932, by Adriaan van Well, ...

s of

sailing ship A sailing ship is a sea-going vessel that uses sails mounted on masts to harness the power of wind and propel the vessel. There is a variety of sail plans that propel sailing ships, employing square-rigged or fore-and-aft sails. Some ships c ...

s. These formed part of the masts and

rigging Rigging comprises the system of ropes, cables and chains, which support a sailing ship or sail boat's masts—''standing rigging'', including shrouds and stays—and which adjust the position of the vessel's sails and spars to which they are ...

, and had to withstand rough condition, being flexed by the

wind load Wind engineering is a subset of mechanical engineering, structural engineering, meteorology, and applied physics that analyzes the effects of wind in the natural and the built environment and studies the possible damage, inconvenience or benefits w ...

s they supported, attacked by sea and bad weather, and suffering from

UV degradation In polymer chemistry photo-oxidation (sometimes: oxidative photodegradation) is the degradation of a polymer surface due to the combined action of light and oxygen. It is the most significant factor in the weathering of plastics. Photo-oxidatio ...

from long-term exposure to sunlight. The most important condition for such varnishes to resist was flexing. This required a varnish that was flexible and

elastic Elastic is a word often used to describe or identify certain types of elastomer, elastic used in garments or stretchable fabrics. Elastic may also refer to: Alternative name * Rubber band, ring-shaped band of rubber used to hold objects togeth ...

. Without elasticity, the varnish would soon crack, allowing water to penetrate to the wood beneath. At the time, varnish production was rudimentary and had only simple materials with which to work. It pre-dated the development of modern

polymer chemistry Polymer chemistry is a sub-discipline of chemistry that focuses on the structures of chemicals, chemical synthesis, and chemical and physical properties of polymers and macromolecules. The principles and methods used within polymer chemistry are ...

. The original sort of spar varnish was a "short oil" varnish, in which a small proportion of a

finishing oil A finishing oil is a vegetable oil used for wood finishing. These finishes are a historical finish for wood, primarily as means of making it weather or moisture resistant. Finishing oils are easily applied, by wiping with a cloth. They are also s ...

, usually

boiled linseed oil Linseed oil, also known as flaxseed oil or flax oil (in its edible form), is a colourless to yellowish oil obtained from the dried, ripened seeds of the flax plant (''Linum usitatissimum''). The oil is obtained by pressing, sometimes followed by ...

, was the majority proportion of the varnish. This gave flexibility, even though its weather resistance was still poor, and thus re-coating was relatively frequently required. In modern times, "spar varnish" has become a genericised term in North America for any outdoor wood finish. Owing to modern varnish materials, their weather and UV resistance is likely to be good, but the original requirement for flexibility has largely been forgotten. A common form of modern spar varnish is spar urethane, a polyurethane-based finish intended for outdoor use, where sunlight-, heat-, and water-resistance are desirable qualities.

References

{{woodworking-stub Varnishes Wood finishing materials

See also

References