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

varnish Varnish is a clear Transparency (optics), transparent hard protective coating or film. It is not to be confused with wood stain. It usually has a yellowish shade due to the manufacturing process and materials used, but it may also be pigmente ...

, originally developed for coating the spars of

sailing ship A sailing ship is a sea-going vessel that uses sails mounted on Mast (sailing), masts to harness the power of wind and propel the vessel. There is a variety of sail plans that propel sailing ships, employing Square rig, square-rigged or Fore-an ...

s, which formed part of the masts and

rigging Rigging comprises the system of ropes, cables and chains, which support and control a sailing ship or sail boat's masts and sails. ''Standing rigging'' is the fixed rigging that supports masts including shrouds and stays. ''Running rigg ...

. These 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 benefit ...

s they supported, attacked by sea and bad weather, and suffering from UV degradation from long-term exposure to sunlight. The most important condition for such varnishes was resistance to 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 (notion), elastic used in garments or stretch fabric, stretchable fabrics. Elastic may also refer to: Alternative name * Rubber band, ring-shaped band of rub ...

. Without elasticity, the varnish would soon crack, allowing water to penetrate the wood beneath. Prior to the development of modern

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

, varnish production was rudimentary. Originally, spar varnish was a "long oil" varnish, composed primarily of

drying oil Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be conside ...

with a small proportion of resin, usually

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

and

rosin Rosin (), also known as colophony or Greek pitch (), is a resinous material obtained from pine trees and other plants, mostly conifers. The primary components of rosin are diterpenoids, i.e., C20 carboxylic acids. Rosin consists mainly of r ...

. This gave flexibility, even though its weather resistance was still poor, and thus re-coating was required relatively frequently. 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

Varnishes Wood finishing materials {{woodworking-stub

See also

References