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.

These advantages also point to some potential disadvantages. Fast drying sometimes results in more prominent brush strokes. Some clients prefer the amber color of oil-based polyurethanes. Finally, water-based clear finishes always raise the grain of the wood. This increases the sanding time, which is an additional cost.