A.Painter Dan Greenough, a member of PaintCraft Associates, a San Francisco Bay-area guild of professional finishers, responds: I have found that with most water-based varnishes, an extra coat is required for adequate coverage and protection of the surface. According to Flecto, a manufacturer of varnishes (800/635-3286), their water-based Varathane Diamond Finish is "very close" in hardness to their oil-based Liquid Plastic Interior Wood Finish. Experience and logic tell me that most water-based clear finishes are not quite as hard as their conventional oil-based equivalents.
Water-based finishes have some definite advantages. Because they have relatively little odor, they are appropriate for use in occupied homes where the clients are sensitive to odors. Water-based finishes dry quickly, allowing several coats to be applied in one day. They also dry clear, without the yellowing associated with oil-based polyurethanes.
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