If you used water-based wood finishes years ago and gave up in frustration, give them another try. Newer versions have many advantages over solvent-based finishes: They dry much faster, so less dust can settle into the wet coat, and there's less waiting between coats. Cleanup takes soap and water, not chemicals. They're low odor, pose no fire hazard and are better for the environment.
But water-based finishes aren't perfect. They raise the grain and are very sensitive to temperature and humidity. They're nonyellowing, which is good, but they can produce a bland appearance on darker woods.
To help you achieve a great finish every time and avoid the pitfalls, here are my top 10 tips for using water-based finishes.
Oil and water don't mix. Water-based poly can have adhesion problems when applied over an oil-based stain that's not thoroughly cured. That's why I always apply a barrier coat of dewaxed shellac to seal oil-based stain. After the shellac dries, a light scuff-sand will leave an excellent surface for the poly to grip.
The instructions on the can will indicate that you can apply a water-based clear coat right over an oil-based stain if the stain has thoroughly cured. However, the curing time can be several days, especially with an open-grain wood such as oak where the stain can sit uncured deep in the pores. Play it safe and seal the stain with shellac. Zinsser SealCoat is a dewaxed shellac available at most home centers and hardware stores.
Buy a top-quality, fine-bristle nylon brush for spindle work, inside corners and narrow edges. The nylon bristles won't absorb water from the finish and become mushy like natural bristles will. I use a Golden Taklon brush, although I'm sure there are other ones available. Each fiber is extruded to a point to resemble a natural bristle. The brush is very soft, and the variable fiber diameters create more space for holding material, meaning fewer dips in the can. You can get a high-quality nylon bristle brush for $18 to $30 at homesteadfinishingproducts.com. (And for that kind of money, plan on taking care of it!)
Synthetic wool is a must-have product with water-based finishes. Traditional steel wool will leave behind bits of steel, which will react with the water and leave rust stains in the clear coat. Synthetic wool comes in various grades and is readily available where water-based finishes are sold. I use coarse to medium synthetic wool between coats. To rub out the last coat, I turn to fine and extra fine. Synthetic wool is available at home centers, hardware stores and woodworking stores.
The low odor of water-based poly makes it an ideal choice for refinishing your existing kitchen cabinets in place. It doesn't matter what the old finish was, as long as you prep the surface properly before applying the water-based product. First use a degreaser cleaner like Formula 409 or Fantastik to clean away any buildup of grease or cooking oil. Scuff-sand the old finish with fine synthetic wool, then seal with Zinsser SealCoat. Sand the seal coat with fine synthetic wool, then brush on two to three coats of water-based poly to complete the job.
Unless you're using a brand new can of poly, always strain it with a medium-mesh strainer before applying it. Once the finish is used, it will be polluted with little bits of dried or semi-dried varnish, which will wreck your new finish. Stands and replacement meshes like the ones shown are available at woodworking stores and online.
Water-based finishes are more sensitive to temperature and humidity than their oil cousins. It's best to apply your water-based poly when the air temperature is between 70 and 80 degrees F and the humidity is below 70 percent. If the air is both hot and dry, the poly may set so fast that it will be difficult to maintain a wet edge as you brush, or the film may not level properly before it sets.
The solution is to add an extender to slow the drying time. This is especially useful when you're coating a large piece like a dining table. One choice is General Finishes Dry-Time Extender, No. 21217, sold at rockler.com. Floetrol is another great additive for slowing things down. It's designed for latex paints but works great with satin or semigloss water-based poly and is readily available at paint stores.
Water-based poly dries waterclear and can leave wood with a cold look, especially on dark woods like walnut. To get the warm glow of oil-based poly, add a few drops of dye. Transtint Honey Amber is a great product (No. 21979; from rockler.com). Make a weak solution of dye and water, then stain the wood before you apply the poly. Believe it or not, you can also add dye directly to the poly before you brush it on.
A third coloring option is to seal the raw wood with wax-free shellac, then topcoat with water-based poly. Whichever method you choose, experiment on scrap wood to make sure you'll get the look you want.
Dry wood can aggressively suck up dye or stain, making it hard to control the color penetration. The result can be a dark, blotchy mess. For added control, try wetting the wood with distilled water right before you apply the dye or stain. (Be sure you've raised the grain first.) The increased open time makes the color easier to control. A household pump sprayer or sponge works great.