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The two products – both useful – are quite different.
D.Going back at least 100 years, the term “lacquer” refers to a non-crosslinking finish that is thinned with lacquer thinner. The most common type is nitrocellulose lacquer.
In the late 1980s, water-based (or water-based) finishes became available and some were labeled “lacquer”. The reason, as one manufacturer confided at the time, was to make carpenters believe they were using a familiar finish, which applied and behaved like the traditional lacquer they were used to. This may make them more likely to try it.
To justify the name, the manufacturers claimed that their water-based finish “burned” like traditional lacquer. That is, each newly applied coat dissolves into the previous coat, effectively creating a thicker coat. So the equivalence example was burning.
To some extent this is true. The water-based finishes bond fairly well to previous coats, but the similarities end there. In virtually every other major quality, the two finishes are very different and should have different names to avoid confusion. Manufacturers, writers and teachers should stop referring to water-based finishes such as lacquer or water-based paint.
The biggest difference, of course, is that water-based finishes contain a lot of water and paint doesn’t. Consider these consequences of water.
■ Water lifts the grain of the wood. To get a smooth final result you need to sand the raised grain and do it without sanding the wood or a stain. While you should also sand the first coat of lacquer sanding paint or sealer, it’s much easier than smoothing the raised grain caused by water.
■ The water-based finish is much more sensitive to temperature and humidity than paint. There isn’t much you can do to control the dryness rate of the water-based finish other than controlling the temperature and humidity in your shop, which can be expensive. Conversely, the drying rate of the paint can be controlled by adding paint retarder in hot or humid conditions and acetone in cold conditions.
■ Even at moderate temperatures and low humidity, water evaporates more slowly than paint thinner, increasing the risk of casting and sagging. Additionally, most paint thinners contain six or more solvents that evaporate at different rates, further reducing the likelihood of sagging and sagging.
■ Water-based finishes often contain coalesced particles that can ruin your finish; this is not the case with lacquer. So it is doubly important to filter water-based finishes before use.
Although these characteristics can be seen as negative, water contributes a very important positive quality: the lower odor. Water-based finishes are much less smelly and irritating to apply than paint.
A second important difference is the resin used.
Lacquer is made up of long filamentous molecules of nitrocellulose that become entangled in liquid form (like spaghetti mixed in a pot of water) and form a hard film after all the solvent evaporates. This film can be easily returned to its liquid form by bringing it into contact with paint thinner.
Conversely, water-based finishes are composed of emulsified droplets of acrylic or polyurethane resin that join and stick to each other when water (which evaporates first), then a solvent evaporates. Inside the droplets, the resin molecules cross-link, that is, they form chemical bonds, but with a few exceptions the droplets themselves stick to each other. They can be separated with different solvents, but with more difficulty than with lacquer.
The different resins and how they cure represent significant differences in how the two finishes can be handled.
■ Lacquer can be invisibly repaired by melting (with heat) or dissolving (with solvent) more lacquer in the damage. Due to the crosslinking within the water-based droplets, however, there is usually a visible border with water-based finishes. This border must be masked with color, often a difficult task.
■ Lacquer is easier to scrub to a uniform sheen because spaghetti-like molecules are easily separated with an abrasive, while cross-linked molecules within water-based droplets resist separation. They need to be torn apart, creating a more uneven shine.
■ Also due to crosslinking, water-based finishes are more difficult to peel. The paint can simply be dissolved and removed with paint thinner or paint stripper.
■ Water-based finishes are also more difficult to clean with a spray gun. You usually have to take it apart to remove all the finish. Conversely, the paint can be left in a spray gun for a week or more and still be completely clean when more paint, or paint thinner is sprayed.
Although crosslinking within the droplets can be seen as a problem for handling water-based finishes, it is a plus for better abrasion resistance and also some solvent and heat resistance. This is due to the fact that the entire surface area is made up of cross-linked molecules except where the droplets join.
The coloring and filling steps are more difficult with water-based finishes than with varnish. For example, paint can be infinitely diluted with a paint thinner to produce toner while water-based finish cannot. Adding too much water to high surface tension causes imperfections in the water-based finishes.
Also, due to the ability of the lacquer (due to the lacquer thinner) to penetrate through layers of color (stain, polish, pore filler) and to bind to wash coats or complete finishing coats underneath, it is possible to build a finish to multicolored steps which has a significantly higher film integrity (resistance to separation in the color layers) than that obtainable with a water-based finish.
As a result, factories often do the decorative steps with a solvent-based finish, then overcoat with a water-based finish to comply with VOC laws.
Finally, one of the most significant differences is the color, or the lack of it, the finish adds to the wood. Lacquer adds a warm orange tint while most water-based finishes add no color.
The orange coloring warms darker woods such as walnut, cherry and mahogany in contrast to the water-based finishes, which soften the color (unless a stain is applied). On the other hand, most water-based finishes retain the white coloring of woods such as maple, birch, ash and pine, which I find attractive.
I hope I have stated that the water based finish is very different from lacquer and should not be called lacquer. PWM
Bob is a contributing editor to this magazine and author of “Flexner on Finishing”, “Wood Finishing 101” and “Understanding Wood Finishing”.
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