Difference between Lacquer, Varnish and Polyurethane
The three common types of finish you get on furniture are lacquer, polyurethane and varnish. Sometimes (but not often) you get furniture that is painted. But what are the differences between these types of finish?
Lacquer Finish For Furniture
Let’s start with lacquer. This is a clear nitrocellulose dissolved in solvent, that is applied to woods to provide a clear protective coating that will allow the beauty of the wood underneath to show through.
Occasionally you get lacquers that are stained with pigment to provide a darker coating. Some lacquers have shellac dissolved in the solvent.
You can apply lacquer to wood or on top of a sealer made specifically to sit underneath lacquer, but you cannot apply lacquer to a formerly polyurethaned or varnished finish – it just won’t adhere. It can also be applied to metals, hence the reason you find decorative lacquered tin boxes.
Lacquers provide a really hard wearing finish that makes the wood resistant to damage from water, acids or alkalis. Lacquer is usually sprayed on. When applying lacquer, usually just a single coat is sprayed on – it’s pointless adding additional coats, as the new one simply dissolves the existing coat to form a single coat again. Lacquer is popular as a furniture finish as it is fast-drying.
Varnish is a resin that is dissolved in a solvent with drying oil. It is usually clear (though some varnishes come with pigment). As it dries it forms a protective film over the wood that it has been applied to.
It can only be applied to wood, it doesn’t adhere to metals. Varnish is usually brushed onto the wood rather than sprayed. Because the varnish brush strokes tend to be visible in the finished product, it’s important to apply it with a steady hand in a dust-free environment.
With varnish the more layers you apply, the more protection you provide to the wood. Varnish is slow drying, so a lot of patience is needed when varnishing wood.
Polyurethane Finish For Furniture
Polyurethane is varnish made with polyurethane resin. Polyurethane was invented in laboratories during World War 2 and is a polymer formed by combining a diisocyanate with a diol.
It is incredibly tough and seals woods and metals to make them resistant to heat or water. It also resists acids and alkalis and is ideal for protecting anything on a seafront, withstanding moist salted air. Polyurethane varnish provides a tougher seal than standard varnish.