What is the difference between Lacquer, Polyurethane, and Varnish?

Question

Also, what is the best use for each?

Answer 1

In a general sense, lacquer is a clear or coloured coating, that dries by solvent evaporation and often a curing process as well that produces a hard, durable finish, in any sheen level from ultra matte to high gloss and that can be further polished as required. In a narrower sense, lacquer consists of a resin dissolved in a fast-drying solvent which is a mixture of naphtha, xylene, toluene, and ketones, including acetone. The word "lacquer" comes from the lac insect (Laccifer lacca, formerly Coccus lacca), whose secretions have been historically used to make lacquer and shellac. In America today the word lacquer refers to nitrocellulose, and little else; most other coatings are known as "varnish". In the UK however, the general rule is if you spray it, it's lacquer - if you brush it, it's varnish. All factory finished furniture these days is therefore lacquer (pigmented, tinted or clear).


A polyurethane is any polymer consisting of a chain of organic units joined by urethane links. It is widely used in flexible and rigid foams, durable elastomers and high performance adhesives and sealants, fibers, seals, gaskets, condoms, carpet underlay, and hard plastic parts. Polyurethane products are often called "urethanes". They should not be confused with the specific substance urethane, also known as ethyl carbamate. Polyurethanes are not produced from ethyl carbamate, nor do they contain it.



Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss sheens by the addition of "flatting" agents. Varnish has little or no color, is transparent, and has no added pigment, as opposed to paints or wood stains, which contain pigment and generally range from opaque to translucent. Varnishes are also applied over wood stains as a final step to achieve a film for gloss and protection. Some products are marketed as a combined stain and varnish.

After being applied, the film-forming substances in varnishes either harden directly, as soon as the solvent has fully evaporated, or harden after evaporation of the solvent through certain curing processes, primarily chemical reaction between oils and oxygen from the air (autoxidation) and chemical reactions between components of the varnish. Resin varnishes "dry" by evaporation of the solvent and harden almost immediately upon drying. Acrylic and waterborne varnishes "dry" upon evaporation of the water but experience an extended curing period. Oil, polyurethane, and epoxy varnishes remain liquid even after evaporation of the solvent but quickly begin to cure, undergoing successive stages from liquid or syrupy, to gummy, to tacky, to "dry to the touch", to hard. Environmental factors such as heat and humidity play a very large role in the drying and curing times of varnishes. In classic varnish the cure rate depends on the type of oil used and, to some extent, on the ratio of oil to resin. The drying and curing time of all varnishes may be speeded up by exposure to an energy source such as sunlight or heat. Other than acrylic and waterborne types, all varnishes are highly flammable in their liquid state due to the presence of flammable solvents and oils.

Answer 2

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What is the difference between Lacquer, Polyurethane, and Varnish?
Also, what is the best use for each?

Answer 3

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Shellac is as has been said made from the larvae of an insect dissolved in alcohol. It is used both as a furniture finish (and a very good one) and sealer (both for furniture and covering spots that you think might bleed through paint). It comes in three varieties, white, orange, and pigmented. White is what most people use and unless the can says it is ready to put on, you may want to thin it to a watery consistency. It dried fast and thus avoids gathering all of the dust and bugs that are close by. You can use clear, white or orange, shellac as a sealer depending upon the final color you are looking for. The white pigmented shellac is use for sealing like on walls where there are spots or even on bleeding knots. It is thinned with alcohol which can be listed as Shellac Thinner or Denatured Alcohol. Don't buy more shellac than you have to use in a short time. It will spoil in the can and if you open a can of spoiled shellac, it will smell to high heaven and because of the gasses formed inside of the can, it can actually explode on you - not a fiery explosion, but certainly something you don't want. Shellac only comes in a gloss. If you want it flattened, or satin finish, use 0000 steel wool and rub it out. Lacquer is a nitrocellulose product and is thinned with lacquer thinner. It is used for furniture finishes as well as some metals. It used to be used on automobiles. Like Shellac, it is hard. It dried rapidly. It is available in a brushing lacquer and a spraying lacquer. Lacquer can "blush" when brushed or sprayed. That means that it will take on a whitish appearance, but that can be stopped two ways: Spray some more clear lacquer thinner on top of it, preferably having some retarder in it, or use retarder in the lacquer when you spray it. Lacquer dries very fast and the blushing is caused by the outer surface drying faster than the rest of the finish. There are non-polyurethane finishes in Varnish but you seldom see them any more. You will be selling Min-Wax, but I would not use that on the inside of my garbage can. I simply don't like it. That is me, however, and the housewife who is refinishing an old piece of furniture will ask for Min-Wax. Make her happy and sell it to her. Polyurethanes came onto the market in the late 1950s or early 1960s. It is an incredibly hard finish and is available, like lacquer, in flat, satin and gloss finishes. There are water soluble polys that I would now sell over the regular ones because they dry faster. Regular polys take at least 8 hours to dry, thus gathering all of the bugs and dust that will be available during that time. For someone who does not know how to use lacquer, either brushing or spray, sell them water based poly. Spar varnish is supposed to be use when a heavier duty varnish is required. It gets its name from varnishing the spars on a boat or ship. I doubt if you have a non poly spar urethane, but I would not use the Min Wax product outside at all. It does not weather well. Actually Varnish is a collective term and includes shellac, varnishes as we know them today, paints, and lacquers. Frankly, I buy shakey old furniture and rebuild it. You can't get good furniture today, so I get stuff made in the late 19th century up to about 1930 or so. To finish, I almost always spray a gloss lacquer and de-gloss it to my liking with 0000 steel wool. I have only been doing this for about 50 years and my finishes last since I am still using most of what I did 40-50 years ago. I could be enticed to use a water based poly and may well use it on something I am doing right now, but that is mainly because my shop is in the drive way now and it takes too long to get the compressor out.

Answer 4

What Is Varnish