Minwax polyurethane is a protective varnish that is used to seal the wood stain. It's an oil-based, clear finish that's applied in several coats after staining, and is fast-drying and appropriate for any indoor wood surfaces, such as cabinets, bookcases, trim, and doors. However, if you're not careful, small air bubbles can mar the beauty of the finish permanently. To prevent air bubbles from occurring at all, follow these tips.
1. Stir the Can Prior to Use and Take Your Time
Resist the temptation to shake the polyurethane prior to use. Stir the contents instead with a paint stick in a gentle, swirling motion. This will reduce the chance for bubbles to form and be applied to the wood surface you are working with.
The creation of bubbles is more a function of the motion and speed of the brush than any other factor. What this means is that if you take your time when applying the polyurethane finish to the wood, there will be less of an opportunity for air bubbles to form.
2. Use a Natural Bristle Brush
There are many different types of brushes that can be used to apply finish to the wood. However, to reduce the chance for bubbles to form, you should use a natural bristle one. This type will not create foam or bubbles when used to apply the finish.
3. Avoid Creating Foam
Apply the Minwax polyurethane finish with even strokes to avoid creating foam. The foam will obviously cause bubbles to form and create a messy, uneven result.
4. Tip-off Finish
Use a “tip-off” motion when stopping the application of finish on the wood. Tipping off occurs by simply running the brush stroke across the wood and lifting the brush upward at the end of the stroke. Run the brush lightly over the area to pull the finish over the surface. This creates an even application of the finish and doesn't cause air bubbles the way other techniques can.
Be aware that following this advice and steps recommended by the manufacturer may still not eliminate all of the bubbles. In those instances where they still occur, allow them to hopefully dissipate on their own. Any remaining imperfections in the finish can be removed with mineral spirits for a period of up to 20 to 30 minutes after drying. Gently wipe the bubbles away and, if necessary, reapply the polyurethane finish to the area.
Following these steps should help minimize the creation of air pockets and make your wood finishing projects more successful.