Paint vs. Varnish
Paint and varnish are two commonly used finishes applied to wood and other materials. Here is a comparison between them in terms of appearance, application, protective properties, and drying time.
Paint consists of a colouring pigment suspended in an oil or water solvent (the "vehicle"), a resin that binds the pigment particles together and provides adhesion to the surface being painted. Paint is a "film-forming finish" in that it forms a thin layer that lies on top of the surface to which it is applied with minimal absorption below the surface. It is used to both protect and decorate surfaces.
Paints fall into two broad categories: water-based latex paints, and oil-based paints or "alkyds." Most of the liquid portion of latex paints is water and for oil-based paints, the liquid component consists of petroleum distillates and other organic solvents. About three-fourths of all paint sold today is of the latex variety. Advantages of these paints include easy clean-up with soap and water, faster drying, and less likelihood of cracking.
Varnish is a clear film finish that is made from oils and resins. It is one of the more durable clear finishes, providing excellent protection against water, water vapour, chemicals, and heat. Varnish is applied as a topcoat to stained wood to protect the wood, to make it easier to clean, and to impart a nice shine to the surface. It is used when one wishes to retain the natural beauty of the wood. The characteristics of varnish are determined by the type of resin, type of oil, and the proportion of resin to oil. The oils used in varnish include linseed oil, tung oil, soybean oil, walnut oil, and safflower oil.
Most varnishes use a synthetic resin, usually alkyd, phenolic, or polyurethane. Alkyd is the most common type of varnish for interior applications. It is not as tough as phenolic varnish, but it is cheaper and doesn't yellow quite as much.
Varnish imparts a sheen to stained or bare wood and does not obscure the wood's grain or texture. Some varnishes, particularly oil-based ones, have a slight amber colour that gets more pronounced over time. The effect is most noticeable with light-coloured woods such as maple or pine. Varnish comes in three different sheen levels: satin, semi-gloss, and gloss.
Paint can transform the appearance of an object. Depending on the colour and concentration of the paint, it can completely obscure the grain and texture of wood. It also covers up knots and other irregularities. Paint comes in four basic sheens: flat, satin, semi-gloss and high gloss.
Protection and Durability
For interior applications, paint and varnish perform both provide decent protection against water and solvents.
For outdoor applications, paint is more protective and longer lasting than varnish. The pigments in paint provide superior UV resistance compared to varnish and other clear finishes. Varnish will last only 1 to 2 years on wood exposed to the full sun compared to 7 to 10 years for paint.
A primer paint coat is usually required before applying topcoats of paint. If the surface is not primed, the paint will not adhere to the surface and it will peel off very easily. Paint can be applied with a brush, a roller, or a spray gun.
Varnish can be applied directly to bare or stained wood that is free of dust. The traditional way of applying varnish is with a brush but it can also be sprayed or wiped on. Many varnishes require two to three coats for a smooth finish.
Paint varies considerably in drying time, depending on how it is applied (spraying versus brushing) and whether it is water-based or oil-based. A brushed-on oil-based paint can take up to 8 hours to dry whereas a sprayed-on paint may dry in less than 1 hour.
One of the biggest challenges with varnish is its long drying time which allows pesky dust particles to settle on the surface. You can generally figure on 24 hours for varnish to dry although newer water-based formulations and polyurethane often dry more quickly.