Woodworker's Journal 2011-35-Winter, страница 49
Compatibility Water-based coatings will adhere well on clean raw wood, over dye stains and over some pigments, but some brands may peel off of some stains. If there is any grease, oil, wax or other contamination on the wood, the finish may create uneven puddles called fisheyes. You can avoid both of these problems by sealing the stained or raw surface first with a thin coat of dewaxed shellac or wax-free Zinsser SealCoat". One thin coat brushed, sprayed or wiped on and off will seal in any contamination and guarantee that the finish will adhere over any stain. The same treatment works if you want to add a coat of water-base over an existing finish, such as old varnish or polyurethane. Clean the surface, sand lightly, and seal it with de-waxed shellac. Applying Waterbornes The most common problem I see among waterborne users is that they put on too much. Apply it too thickly and it will not lay out well, and it might even turn cloudy from excess water trapped in the drying film. The best advice I can offer you, whether you are spraying or brushing, is to put on less than you think you should. Each coat should leave the surface barely wet Let it dry overnight Pay attention to your finishing environment too. Water-based finishes are more finicky than solvent-based ones, and they prefer a warm, dry room. You'll get better results if the temperature is 70 degrees or warmer, and the relative humidity is around 50% or lower. Cold temperatures (below 60 degrees) or very high humidity (above 80%) can prevent the finish from curing properly and will make it harder for the film to level itself. The water in the mixture will make the first coat of finish raise the grain on raw wood, making it feel rough to the touch once it is dry. Sand it lightly to bring down the "fur" and it will not rise again after that It is a good idea to sand continues on page 50... Water-based finishes, while offering plenty of advantages to the home woodworker, , do have their quirks and drawbacks. ¥ |
