Raise the Grain First
Always raise the grain on raw wood before applying a water-based finish. Simply brush, sponge or spray on some distilled water and let it dry thoroughly (overnight is best). Then, resand with your final grit paper to break off the whiskers. Now when you apply the finish, the grain will stay down.
Seal Oil-Based Stain
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 you should 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.
Lay it Down and Leave It
Water-based poly should be laid down with a couple of quick strokes. Don't worry too much about the appearance of the wet finish. It will look awful at first, but water-based poly has an amazing ability to pull tight as it cures, like shrink wrap. The brush marks will disappear—promise. If you go back and try to rework the film, you're likely to cause a big mess. Resist the urge. If you see a dust speck, just leave it alone and fix the problem later with sandpaper and another coat.
Choose the Right Applicator
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. We like the Golden Taklon brush, although 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 Taklon bristle brush for $18 to $30 at homesteadfinishingproducts.com. (And for that kind of money, plan on taking care of it!)
Use Synthetic Abrasives, Not Steel Wool
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. Use coarse to medium synthetic wool between coats. To rub out the last coat, turn to fine and extra fine. Synthetic wool is available at home centers, hardware stores and woodworking stores.
Refinish Kitchen Cabinets With Water-Based Poly
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.
Strain Your Poly First
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.
Use an Extender in Hot, Dry Conditions
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, available at amazon.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.
Add Color for the Look of Oil-Based Poly
Water-based poly dries water-clear 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 (available at amazon.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.
Mist Your Wood Before Staining
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; see the first tip.) The increased open time makes the color easier to control. A household pump sprayer or sponge works great.
Water-Based vs. Oil-Based Floor Finish
Both offer good protection; the biggest difference is in appearance.
Water-based polyurethanes provide a clear, neutral finish and have low odor. You can recoat them in two hours and clean your tools with water. If you start early enough in the day, you can apply the recommended four coats and sleep in the room that night.
Oil-based polyurethanes leave an amber glow and require fewer coats. But the five-hour wait between coats and 12-hour wait after the last coat will put a bedroom out of commission for a few days—and you'll have to put up with a strong odor.
Apply Water-Based Poly With a Pad
Water-based poly dries faster than oil, so it's even harder to brush over a big surface. The solution is a paint pad, which applies poly fast and smooth. Just dip the pad into a pan of poly and drag the pad across the surface. Be sure to smooth out any ridges pushed up by the edges of the pad.
Is Your Poly Still Good?
Just because your poly has skinned over in the can doesn't mean you have to throw it away. First check the remaining material to make sure it's clear and particle-free. If the polyurethane has crud in it, try filtering it through cheesecloth. Then try brushing it on scrap wood. If it goes on fine, use it.
If the poly is water-based and too thick, thin it by adding water (no more than 10 percent). You can also thin solvent-based poly by adding up to 10 percent mineral spirits, but only if you live in a state that allows it. Some East Coast states and California prohibit users from adding solvents after the can is opened. In that case, you'll have to recycle the old stuff and buy a fresh can.
Always test thinned polyurethane on scrap wood before applying it to your project. Chances are it will work just fine. But if it doesn't look right, buy fresh material.