Wash Coat #2: Waterborne Finish Coatings
As previously mentioned in Preventing Blotching Using A Wash Coat #1, most any standard finish can be used as a wash coat. These are Lacquer (both waterborne and solvent type/nitrocellulose), polyurethane (both waterborne and oil based), Oil-based Varnish, and Shellac.
The above being said, lets talk Waterbourne. It really makes no difference which you use waterborne lacquer, waterborne shellac or waterborne polyurethane since they all are simply water-borne acrylics—none are really lacquer, shellac or polyurethane. These are simply terms created in the marketing department intended to stimulate sales.
In Understanding Wood Finishes, Bob Flexner puts it this way:“
“(Water-borne finishes are) often called lacquer, shellac or varnish for marketing reasons. It makes an entirely new type of finish seem familiar. Water based is often called polyurethane for the same reasons when some polyurethane resin is blended with the usual acrylic resin. This interchangeability of names adds to the confusion about finishes. When you hear or read that someone varnished a table, it could mean he or she applied either of the evaporating finishes (shellac or lacquer), a reactive finish (varnish), or a coalescing finish (water base).”
With nothing but the highest respect for Bob Flexner, I am a bit less charitable (his book is very high on my recommended list when it comes to explaining finishes, what they are (and aren’t), and how they work). I believe there may have been a time when the “name game” was intended to foster a degree of familiarity. However, water-borne finishes are no longer new, and their basic formulation has not changes since they were first introduced. The “creative naming” taking place today is done with the plain and simple intention of misleading—and, it works.
While it is true that the Minwax product (and similarly labeled polyacrylics) contain a small amount of urethane resin, the dominant resin in all water-borne finishes is acrylic. There is virtually nothing about these so called “water-based polyurethane” finishes that can be compared to oil-based urethane resin varnish.
Therefore, what you have read about the negative attributes of poly applies only in the most peripheral sense to water-borne acrylics with urethane resin added.
The only major similarity is that (acrylics) should not be applied over shellac that contains wax.
In the context to a question will “lacquers do the job” we are, in effect, wondering if a water-borne acrylic from a different can and sold under a different name do any better. Again, our “lacquer” isn’t lacquer unless we adopt a definition of lacquer that is so broad that it can be wrapped around any liquid finish that dries or cures to form a finish film. (If we do that, water-borne poly will also be lacquer.) In this instance the manufacturer uses the term “pre-catalyzed” in an effort to link its product with the true pre and post catalyzed lacquers.
Again, this is nothing but marketing subterfuge. Just as we are also treated to “Tung Oil Finishes” that contain nary a drop of tung oil; and to TV woodworkers who claim to use some magic oil when in reality they are simply applying wipe-on poly-whatever-thane. In the world of finishes, marketing claims and fact tend not to reside together. In all likelihood, the manufacturer has simply added a “hardener” to the finish. This is a chemical that creates a sort of “cross-linking” reaction within the finish for the purpose of making the cured film more durable in the face of heat, solvents, acids, alkalis, water, and water-vapor (the typical water-borne finish does not do nearly as well in the face of these hazards as an oil-based finish). This hardener is frequently added to water-borne finishes that include KCMA finish durability success in their advertising. The downside is that this hardener is very toxic, thus eliminating one of the benefits of using a water-borne in the first place. Furthermore, the finish film is still inferior to oil-based varnish in the face of these hazards.
Finally, it is not my point that there is anything “wrong “with any of the finishes that you propose to use. They are what they are and they are defined by their own set of advantages and disadvantages dependent on the proposed application.
But, to my point about the similarity (virtual sameness) of water-borne finishes; all water-borne finishes share three common ingredients that make up nearly 100% of the contents. Further, the proportion of these primary ingredients tends to be remarkable uniform from brand to brand. These components are 1) water (typically 50% to 60%), 2) Acrylic Resin (usually somewhere between 20% and 30%), and 3) Glycol Ether (about 10%).
In those water-borne finishes that are advertized as “water-based poly” the acrylic resin is typically reduced on the order of 5% to 7% to make room for an equal amount of “polyurethane”. Other chemicals are added in significantly lesser amounts for the purpose of improving various properties. For example, flow-out in water-borne products formulated to be padded or brushed; and, to reduce foaming in those designed to be sprayed.
In other words, you will get the same result with Target, General Finishes, M.L. Campbell, Mohawk, etc. My point is that the using one or the other, for whatever reason, will not pose a problem in terms of the ability to provide a finish offering equal properties and capabilities. There is a whole world of functionally equivalent water-borne finishes no matter what label is on the can.
Wash Coat #2: Waterborne Finish Coatings
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-- Respectfully, Paul